IGS Summer 2019 Issue

Intelligent Glass Solutions • An IPL magazine

SPECIAL GPD 2019 EDITION

INTELLIGENT GLASS SOLUTIONS

SUMMER 2019

COLLECTORS ITEM

Summer 2019

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Cover picture: European Patent Office, Netherlands 2018 © Ossip Van Duivenbode Ateliers Jean Nouvel + Dam & Partners

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Ian Ritchie designing with the mind in mind GPD 2019 presentations • MAKE Architects smarten the alumni experience • Saint-Gobain getting bigger and bigger

IGSMAG.COM WELCOME TO OUR WORLD

Welcome to

our world!

Over the next 10 years 18 billion sqm of space will be designed by architects and engineers to shelter 1.5 billion people. An unbelievable stat provided by our hardworking brothers and sisters at ArchDaily and worth repeating to you here.

We work with pioneers who are spearheading technology in this transforming sector, and strive to bring their findings and results to our readers, fast.

IGS magazine has reflected the industry’s momentum over the past 14 years by publishing expert testimony on the central issues that really matter

Intelligent Glass Solutions magazine (IGS) serves as the source for inspiration, innovation and building design trends. With igsmag.com we pledge to complement the print magazine and bring you the latest news, technologies, developments and projects in the architectural glass and facade design and construction field. Our readers can enjoy absorbing content from authentic leaders of the industry, featuring amazing projects and case studies predominantly focused on glass, with informative and educational content that is rarely obtainable elsewhere.

Publisher’s Blurb Everybody loves to look at the stars in the sky at night, we love to look at the trees and the plants and the flowers. We love to look at people, and yes the birds and the bees, we love to look out of the window, and see life. Ladies and gentlemen allow me to make this bold statement, buildings with glass as we know it today, are on the increase, big time, and rightfully so. We all love to see and hear this.

In this issue of IGS we bring you technical papers from the conference of conferences when it comes to sharing and spreading essential knowledge about transparent architectural structures throughout the industry. The fact that the creator and energy behind GPD, Jorma Vitkala, the man who has been front, centre and all around the edges of this international gathering right from the outset has decided to step down, means GPD as we have known it for the last 25 years and counting, will inevitably change. We wish Jorma all the comfort and happiness in the world as he settles down to enjoy the evening of his life with an expensive bottle of wine, a good cuban cigar, and of course his delightful wife Reika. GPD 2021 will no doubt continue to deliver premium quality content, it will understandably have a different feel and a different spirit, so we will wait with compelling interest to see what surprises lie in store for us and who will be the recipient of the prestigious JVAM 2021 but for now, this issue of IGS provides you with an injection of advanced technology on applications and practices that home in on the industry’s most central issues - Just the tonic you need to invigorate your soul.

As time moves on ladies and gentlemen, please join our super good looking IGS readers and raise your glass to one of the most popular industry giants of our short time on this earth - To Jorma Vitkala!

This is IGS, NOTHING MORE, NOTHING LESS.....NOTHING ELSE!

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Summer Winter 2018 2019 | Intelligent Glass Solutions | 1

IGS Summer GPD 2019 Collectors Item Special Issue

INTELLIGENT GLASS SOLUTIONS

C O N T E N T S

You’re reading IGS Magazine 4

12

Features

GPD sharing technology around the world

4

Ian Ritchie CBE RA: Inside the mind of an architect

28

In his interview with Petra Eckhard co-editor of Graz Architecture Magazine, Ian Ritchie allows us into the inner reaches of his mind as he talks about architecture Advancing Technology.

Agnes Koltay presents a case study on Sky View, a twin tower project in Dubai boasting a skybridge and sky observation deck. Living in the skies is fast becoming the norm in parts of the world.

32

Javier Sanchez-Gil Curved Glass: Reshaping architectural glass with new possibilities.

38

Viviana Nardini presents some effective options and guidelines when considering the design of cold bent units.

45

Enhancing the Light - curved IGU design study brought to you by a group of distinguished academics from Moore & Associates Inc.

51

Benjamin Beer discusses options for complex geometries and investigates cold-bent glass over a single corner.

58

We learn more about complex geometries by means of a case study presented by Frederico Figueiredo, this article focuses on glass balastrades.

62

An engineering approach for the basic design of glazed surfaces under blast waves, This paper is presented by Maffeis Engineering.

12

The titan that is Saint Gobain explains the many advantages of jumbo sized glasses and encourages us to think big.

Executive Boardroom Commentary 20

IGS Interviews Mark Patterson of MAKE architects, experts in the sustainable design of universities, amongst other things. *Exclusive*

*Exclusive*

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Bringing you technology that defines the age.

C O N T E N T S

INTELLIGENT GLASS SOLUTIONS

and these are your headlines 74

82

68

An unusual glass tube façade in Hong Kong gets a Closed Cavity Façade. Martin Teich and his colleagues at Seele walk us through this process.

92

Peter Lenk, ARUP, encourages us to take the next step in structural glass, he says it’s digital design and fabrication.

74

High tec is achievable for everyone! So says Miguel A. Nuñez Diaz and his colleagues who will demonstrate why this statement is so true.

98

Glass bending technology for glasses with sharp curves, Tobias Rist, Fraunhofer Institute for Mechanics of Materials.

82

The tallest, heaviest sliding glass door of all: an extensive case study brought to you by Carlos Machado e Moura & Pedro Borges de Araújo, Jofebar and Porto School of Architecture.

102 Essential: Inspection of glass facades, Barbara Siebert.

108 Glass coatings useful for the prevention of bird collisions, E.A Axtel of Ferro Corporation USA.

Intelligent Glass Solutions • An IPL magazine

Front Cover Image: Image: European Patent Office, Netherlands Photo: © Ossip Van Duivenbode Courtesy of: Saint-Gobain

SPECIAL GPD 2019 EDITION

INTELLIGENT GLASS SOLUTIONS

Intelligent Glass Solutions is Published by Intelligent Publications Limited (IPL)

Summer 2019

SUMMER 2019 igsmag.com

Cover picture: European Patent Office, Netherlands 2018 © Ossip Van Duivenbode Ateliers Jean Nouvel + Dam & Partners

COLLECTORS ITEM

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Ian Ritchie designing with the mind in mind GPD 2019 presentations • MAKE Architects smarten the alumni experience • Saint-Gobain getting bigger and bigger

ISSN: 1742-2396 Publisher: NIck Beaumont Accounts: Jamie Quy Editor: Sean Peters Production Manager: Kath James Director of International Business Network Development: Roland Philip Manager of International Business Network Development: Maria Jasiewicz Marketing Director: Lewis Wilson

Design Director: Antony Parselle Page Design Advisor: Arima Regis Design and Layout in the UK by: aparselledesign Tel: +44 (0) 1727 811842 Intelligent Glass Solutions is a quarterly publication. The annual subscription rates are £79 (UK) , £89 (Ireland & Mainland Europe), & £99 (Rest of the World) Email: nick@intelligentpublications.com Published by: Intelligent Publications Limited 3rd Floor, Omnibus House, 39-41 North Road, London N7 9DP, United Kingdom Tel: +44 (0) 7703 487744 Email: nick@intelligentpublications.com www.igsmag.com

The entire content of this publication is protected by copyright. All rights reserved. None of the content in this publication can be reproduced, stored or transmitted in any form, without permission, in writing, from the copyright owner. Every effort has been made to ensure the accuracy of the information in this publication, however the publisher does not accept any liability for ommissions or inaccuracies. Authors’ views are not necessarily endorsed by the publisher.

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Ian Ritchie: Inside the mind of an architect

Architecture has two distinct phases: The mental dream and reality’s nightmare

Inside the mind 4 | Intelligent Glass Solutions | Summer 2019

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Ian Ritchie: Inside the mind of an architect

Ian Ritchie in conversation with Petra Eckhard (GAM) Ian Ritchie’s architectural programs emerge from the ethos to deliver socially beneficial and ecologically sustainable projects. His London-based office, Ian Ritchie Architects, has won more than 80 national and international awards, several of which the office received in 2018. Early 2018 The Royal Academy of Music in London presented to the public its new performance spaces, the opera house and recital hall for opera and musical theatre. Petra Eckhard (PE) met Ian Ritchie (IR) during his visit to Graz and talked to him about fluid dynamics and the power of poetry in the design process.

PE: Can you describe your design philosophy in three words?

IR: “Sensual, intelligent, egoless.”

And also: “Aphorisms grow shoots.” Meaning, aphorisms set the design process going. The aphorism expressed by this particular phrase is especially important because it summarises my philosophy.

PE: Can you elaborate on that? Why is an aphorism, or more generally, poetic language, a useful tool for architectural design?

this temporal palimpsest, if you like, in your brain about the way the project might appear in the next five years.

And you go through the layers and shuffle aspects of the nascent design around—the client or the site or the environment or the politics or the social responsibility—all these things come into your mind, and it’s impossible to draw something. It’s actually stupid, in my opinion, to draw something too quickly. I suppose if you like language—written language or spoken language—it’s because language is something we have in common and it’s our natural means of communication, the one that we’ve evolved. Everybody more or less understands talking to each other and having conversation, though I do sometimes question the ability of today’s younger society to stay focused on a discussion or an argument.

That seems to have vaporised. But, in my case, I carry on moving the words around until I find what I think is the key to the project, and then I condense that prose into a poem just to get the beginnings of a feeling of what the project might become. If I am very lucky, I write an aphorism, but the aphorism is rarely related specifically to a visualisation of the project. It’s often more about humour. In a way, it’s kind of designing with language.

PE: So, prior to designing a structure, it helps to compose a poem?

IR: Words come before the drawing during my design process, because exploring ideas through words doesn’t lock down a concept too quickly. When you draw something and it locks into your brain, you can’t actually delete it—even if you can burn the paper or throw it away—whereas using words one can find out where one is going, exploring ideas like an archaeologist. You’re looking for the essence of the project, so you’ve got

IR: Half-way through the competition for the UCL Neuroscience Lab I wrote a poem. I have to find it on my phone. This is from 2008/2009 and it is called “Dreaming of a Project,” because we actually wanted to win it. I can read it to you, if you want.

PE: Yes, that’d be great…

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Ian Ritchie: Inside the mind of an architect

Ian Ritchie: “As the banks crashed, the fishing began.

We watched fish fly, new born lambs jump and architects worry about the next job.

Are architects magicians?

Bankers manipulated and spirited away immense substance.

But above all, loyalty and trust.

What do magicians do?

The science of magic?

As neuroscientists research the mind magicians play with it.

How? Did they misdirect us?

Divert our attention?

Blind us temporarily?

Do they fill in the gaps?

Fill in the margins between the frames of a film?

Our eyes see, but not the film.

We see wheels go backwards because we snap the world.

We imagine, we fill in.

And then there is memory.

Under which cup is the ball?

What card did I pick?

Ah, the magician has secrets!

The illusion of free will, And as now with the bankers we trust not the magician?

Sainsbury Wellcome Centre at UCL dusk © Ian Ritchie Architects

Architects are not magicians.

They are dreamers.

My architecture starts in the spaces I create in my mind.

Space is in here and out there, it is a continuum between inside and outside, mental and physical.

Architecture has two distinct phases: The mental dream and reality’s nightmare.

Being an optimist, I know the dream is always there, like the sunshine behind the darkest cloud and the snowflake in the rain.

We can imagine two futures, the one we dream of, and the one left to fate.

Or we can imagine one future, the one we dream of and the one we left to fate.

To be able to read our reality requires a reference. Our dreams.

Some of our dreams questions reality’s reality.

Now I am designing with the mind in mind.

Dreams? I try to build mine avoiding the nightmare.

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Fluy House 2006 © Ian Ritchie

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Ian Ritchie: Inside the mind of an architect

PE: “Designing with the mind in mind” sounds beautiful, as does your use of contrasts in the poem: mental dream/ reality’s nightmare, sun/clouds, mental/ physical, etc. How do you see these metaphors playing out in your design philosophy?

are a really nasty computer virus! Until we recognise that we are actually a virus, and not beneficial to the planet, we won’t change.

So, the idea of going into space to colonise strikes me as completely and utterly daft.

PE: What is your strategy to avoid reality’s nightmare?

IR: I think it is about living an ambiguous life. That is, if you’re sensitive to social issues and environmental issues, you can get depressed quite quickly. At the same time, if you lose a sense of optimism and, in a way, a child’s view of the earth, you won’t find any answers. We’ve got orbiting junk up there and there are programs to try and clean it up. It’s not going to be easy, in the same way that microplastics in the ocean are like a fog. People think that it’s a big pile of plastic sitting in some gyre in the Pacific, but it’s not—it’s a fog throughout all the oceans now.

Two and a half years ago I was on a Russian research vessel in the Arctic. The impact of not seeing any plastic was reassuring. Then I got a phone call from a friend last year who was doing the same trip from west to east, and they had come across the plastic pollution. That’s a major issue, in the sense that we don’t know what the microplastic fog in the ocean will do to life in the ocean - but it can’t be beneficial! If you look at our planet as a giant computer, we (human beings)

IR: An interesting exercise is telling a story of a tree to architecture students: If you describe all the aspects of a tree you realise you are looking at a miracle. Unbelievable.

Genetically a tree species may be the same, but each individual tree is different.

Everything is intelligent: the tree knows how to put out branches to capture the maximum sunlight. It’s driven by the invisible, the moon’s pull, gravity, O2 and CO2 and of course light. This kind of wonder is a metaphor for the proper way of designing. If design is a process, not an end product, the future lies in our ability to grow architecture in a way that is intelligent. It may still have to do with algorithms but it has a lot more to do with the materiality of how we make things.

At the moment, when we look at the building industry, it produces 50% of the carbon in the atmosphere, and apparently 10% of that total is produced by concrete. There are ways of manufacturing concrete that

The tree knows how to put out branches to capture the maximum sunlight.

Eagle Rock © Andy Earl

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Ian Ritchie: Inside the mind of an architect

predict the first and second reflections you’ll get off a building with light or sound.

But in doing so we are always designing out the beauty, with every step we take toward predictability. Therefore, we must invent an aesthetic that suits our age in order to be able to say, “this is beautiful.”

Museo Nacional Centro de Arte Reina Sofía © Ian Ritchie Architects Ltd.

is not as carbon-intensive, but we are not addressing those issues—such as how can we make buildings without digging great big holes in the ground to pour concrete into, or long piles. There are ways of looking at slightly more dynamic buildings that don’t damage the earth and its surface, and that can be stable without having to be super stiff (static). I work with “dynamics”, because that’s how I learned engineering: all structures move, so instead of looking at trying to be absolutely rigid you can look at things that are more flexible but are safe.

That’s how a tree works, interestingly. You bend with the wind a little bit, but obviously our own internal dynamic and our sense of balance have to measure against that. But we spend a lot of energy doing things that are too extreme instead of relaxing and saying, ‘it’s fine.’

PE: Ethical is a key term that one often reads in connection with your designs. You also use it in your mission statement. What does it mean to you?

IR: It’s about sharing values, which could also describe my design philosophy. Today, we seem to value shares more than we share values. These values are the ones that have ethics behind them, whether it’s working with other people, interpersonal relationships, working with the Earth, the planet, oxygen: it’s a way of finding an intelligent way of working with situations.

Nature is unpredictable whereas we spend our time designing predictability, taking away unpredictability. We have to predict the behaviour of a structure, predict the behaviour of air moving in a building, and

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Beauty is simply non-linear. It’s why we like watching a flame, or light on the water on a sea or a river: because you cannot predict the next thing. And that’s the beauty of nature. We will probably have the computing power in the next hundred years or so to measure every single snowflake that falls out of the sky somewhere on the planet, but there is no point so we won’t. That magic of nature—the unpredictable—is beauty. When we say “beauty is in the eye of the beholder” this only refers to the man-made.

PE: Your architectural designs are also quite unpredictable. Your designs cannot be pinned down to a distinctive style…

IR: We don’t have a style. You can’t say that’s an Ian Ritchie Architects building. You wouldn’t know, although you might begin to guess because of the refinement of everything and allusions to visual unpredictability through randomness of the behaviour of light or rocks, or planned ageing. People discover we did this building or that building, and that’s kind of nice. Intellectually we’ve always been outsiders. I never received an overall critical review of our work.

And you can’t get out of bed every morning thinking, ‘I am doing another one of those buildings.’ I would die a death of boredom.

PE: Is this partly due to the fact that you take context analysis or the individual clients’ ideas very seriously?

IR: To give you a quite early example: The first building I did in England was called “Eagle Rock,” a house which looks a little like a crashed airplane in a wood. Peter Cook came down to see and review it and said: “Oh god, the eagle has landed.” He never expected to see a house like that in England.

Possibly California, yes, but not in England.

But it was the result of a conversation I had with the client three years earlier, while I was

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Ian Ritchie: Inside the mind of an architect

renovating the outside of her large villa in Italy. Her passion was orchids, and she would go on trips looking for rare orchids. She mentioned, three years before she did return to England, that she would like a house, and asked me “what would my house be like?” I replied that given her description of her life she just needed a very good suitcase and questioned if she wanted to be encumbered by something anchored to the ground. Three years later we looked for and found a site.

At that point the conversation from three years earlier, about the flying suitcases, became translated through a poem into the idea of packing cases in the landscape with a transparent canopy over top. It was the idea that nothing was anchored to the ground, that she could pick up the house and leave if she wanted to. Of course, as she was getting older, everything became more serious. The concept evolved into the roof being glass and permanent, and the boxes being joined up to give her a house. That’s why it looks like a crashed airplane.

It all comes from starting with the user.

Knowing if we understand the user and what they really want, that’s when we can become skilful architects. If we start the other way around—what’s it going to look like? —you never get to the user. We always start from the inside. It’s the fundamental thing: is the brief correct? You test it against the users.

Often, it’s not what they want. It’s quite rare for scientists, or even musicians or students, to be involved in the process with the architect. You could argue that they are not going to be the ones who will be there, if the building is there for a hundred or two hundred years. However, they are there for that moment, and it’s up to us to understand what they really need and then to think beyond it. And when you do that, the spatial configurations that start to emerge have to be balanced by the context with the outdoor walls of your building, which become walls framing the public spaces of the city. Each street is a room in the city, and it has these walls, and very often architects forget that they are actually creating these framing elements that create a room in the city. Plain clear glass walls facing each other do not create much sense of space. All of that leads you to thinking, to analysing, as you would compose an opera. That’s a nice expression, as opera in Italian, of course, means ‘a

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Terrasson Greenhouse © Ian Ritchie Architects

work’. So, I think that’s more demanding of an architect to think like that than it is to “render and tender.”

PE: What was this process like when you designed the opera house for The Royal Academy of Music? How did the context analysis finally translate into architectural form?

IR: When we came to design the new opera house for the Royal Academy of Music, we started off studying Cremona musical instruments, such as those of Stradivarius and asked: Why were they so special? What was special about the wood, the forest, the way the trees grew, why some but not others; the varnish or how they [musicians] treated it? A rare preconception - we knew we were going to be using wood. Wood has a wonderful ability to reflect sound, depending on its density and is so alive - one wonders if it actually ever stops moving. I went out to find the best joinery company in Britain, because our office knew nothing about wood. The learning curve was fantastic.

When you are designing an opera house it’s all about the voice. The voice is the basis

© Adam Scott

© Adam Scott

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Ian Ritchie: Inside the mind of an architect

of acoustics. When you start producing a sound with your voice, it comes through the many chambers of your body, it then passes through the vocal cords, through your mouth, your tongue and the final space is the one in which you can hear the sound. For me this auditorium was an extension of the body and I knew that wood is the material of that moment when sound emerges. At the opening night it was a relief, because the sound was sensational. So, we nailed it aesthetically and acoustically.

Also, the aesthetic detail geometry of the recital hall and recording space on top of the opera house auditorium came from musical instruments, fairly literally, whether the bow or the tuning end of a violin or a cello. That gave us all the inspiration for designing it. So, the students now have two magical spatial instruments to play with.

PE: Your office is based in London, a global city with a dense, eclectic center with high land prices. Which challenges do you face at the moment?

IR: I think the challenges with London are not its density per se. They are to do with homelessness. That comes from certain political directives, and the numbers of homeless have grown again. I was very surprised to see them on the streets of Graz; I thought Graz was wealthy enough to have the right policies. You can’t stop those who want to live on the street, but the people who end up on the streets due to housing policies I find deeply, deeply hurtful. I think it’s interesting that 90% of the people of this planet are sitting on the ground. Who invented the chair? The Persians. Why they invented it I don’t know, but it’s interesting that the majority of human beings still sit on the ground. When we see someone sitting on the ground in the West, we ask: “Why?” We’ve paved everything and we have invested money; why would you want to sit down there? You get a microcosm of capitalist society in London that’s in your face. It can be quite nasty. A decent society, I think, educates its people, houses its people and looks after them when they are not well or old. A tripod of a civilized society. When all of those become commodities, society is severely undermined: you’re creating an artificial one. Even if you like this form of

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society, it’s unnatural because it is being forced all the time because everything is for sale.

PE: At the moment the economic impacts of Brexit are a major area of debate. What do you think would be the effects of Brexit on architectural production in the UK? IR: All I can comment on is that you have already an attitude, amongst many architects, that could be best summed up as: “I want to do a building on every continent.” That strikes me as a very strange ambition. “I am a global architect, because I’ve done it.” If you ask those architects: “How would you adapt to the culture? Would you adapt to the culture?”

They wouldn’t know how to reply, because the only way they can do these buildings is through wealthy clients who want to get value out of the project. The brief is affected by needing to extract value, as that value is attained through iconic shape, by putting up more apartments in the tower than anybody else could. So that’s the way it works.

As for Brexit, it’s a sign of insanity. When the EU was set up initially as a common market and as an economic model in 1950s, it created the opportunity to open doors between countries. I thought it was a stepping stone to a more open world, and that Europe with its initial six EU member countries would actually be an extraordinary model for the rest of the world to look at.

We all have cultural differences and have been at war with each other for centuries, but somehow, we managed to be intelligent and create cultural exchanges, Erasmus programs—all these things came from the idea of a united Europe, and it doesn’t mean it has to be one homogenous country. If Brittany fell into the Atlantic Ocean, Europe would be a poorer place. You don’t want culture to disappear. The idea that you could bring all of this together as a model for the future of the planet was brilliant. To see the United Kingdom doing what it is doing now is not a United Kingdom decision, it’s an English decision. It’s got nothing to do with Scots.

The Scots don’t attack Europe. When you see the risk of a disintegrating Europe, as a model, I get very sad, I have to say. In a way, I’m explaining that architecture is somewhere way down the list when it comes to Brexit.

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Ian Ritchie: Inside the mind of an architect

PE: You initially came from the world of medicine and then changed to architecture. Many people would consider this a big shift …

IR: In fact, it isn’t. Everything goes through our brains, as we are humans. Medicine is largely looking at the inside of your body, through our brain, and architecture looks at the body in space on the outside, through our brain. So, it’s not a huge jump. If you take your own hand, everything is architecture: you have got a skin, all the services, and you’ve got the structure underneath, and its dynamic is controlled by the brain. It moves. Those are the basic ingredients of architecture. Statics is the German engineers’ language, as is the concept of “nothing moves, and everything is fixed.” Of course, nothing is fixed. Also, the brain is scale-free.

This is why our UCL neuroscience building has all the scales of spaces that (users) want.

Long ones, tall ones, shallow and small ones; and they also know they can change them, up to a certain point. It’s another scientific instrument.

PE: With the UCL Institute of Cognitive Neuroscience project you designed a place for education and research. What is the most important skill students of architecture must acquire?

IR: I have noticed that, particularly since you now pay for your education in the UK and in America, tutors say: “Just do it. Come back tomorrow.” Actually, thinking is the most difficult thing to do. Students are not encouraged to think; they’re encouraged to do. In other words, they’re encouraged to be homo faber (the maker) rather than homo sapiens (the thinker). I think that is part of our disease. The other one, which I’ve learned, again from neuroscientists, is that our brains evolved not to understand the environment; they evolved to understand each other and to communicate with other human beings. Our natural DNA is not to read the environment, which is probably why we make mistakes in the air and make mistakes in the water. At the moment, because education is now a commodity—the production of a university is a commodity and everything is measured, quantified financially or by exam results—it’s not measured by quality anymore. How to learn to think

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is the thing that is missing. I don’t think students are encouraged when time comes into play. I’m quite interested by the student that carries on thinking, and if they haven’t the maturity yet to program their thinking time into their work, that’s understandable because they’re students. Learning to think and making the time to think is vital.

PE: In your opinion, what makes a successful architectural project?

IR: My favourite architect of all time is Sinan.

He was the architect to the Ottoman Empire.

He became an architect at 50, and before that he was an engineer. One could say he was fortunate in that he had the richest client in the world for fifty years. Sinan was taken into the army in his twenties and had a natural ability to analyse problems and solve them, and he understood geometry from a young age. This included geology, water supply, drainage, boat building, engineering and organising teams to work together.

Working together well where no individual is the owner of the work is the secret. There are wonderful examples of his work which have to do with the Ottoman Empire expanding to the West. In particular they had problems with bridges, and particularly with one bridge that kept collapsing. Many engineers were trying to solve it, and he looked at it and said: “We just widen the river to slow the water speed down.” It is all about the infrastructure.

He understood that.

PE: Thank you for the interview.

Petra Eckhard PhD is a senior scientist at Graz University of Technology and co-editor of Graz Architecture Magazine (GAM).

© Ian Ritchie Architects Ltd.

© Grant Smith

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Advancing Technology: Saint Gobain

Think

BIG 12 | Intelligent Glass Solutions | Summer 2019

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Advancing Technology: Saint Gobain

Sheer transparency up to 18 metres Awe inspiring large format glazing in architecture offers users a sense of vast openness. The market is striving towards longer dimensions and superior quality, while the design community continues to reap and celebrate the benefits of incorporating oversized glass panels into their creative endeavors.

Transparent building envelopes remain highly desirable in contemporary design, offering aesthetic appeal, visually striking views, and occupant comfort with a distinct connection to nature outdoors.

Providing vast creative freedom and opportunity, innovative large format glazing offers building stakeholders the privilege to dream big and the confidence to take the plunge.

Large glass installations shape the architectural character of a building both from an interior

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perspective as well as on the exterior envelope. From inside, the boundaries increasingly dissolve while daylight floods the space. Outside, the large glass faรงades appear seamless and monumental. The glass industry boasts an impressive and innovative range of large span glazing technology, using the highest quality processing, precision and finishing.

Large glass in history Extra-long glazing is closely linked to architectural

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Advancing Technology: Saint Gobain

Left: Transport by hand of a large raw glass pane poured at Saint-Gobain Glass site Chauny in 1878 for the Expo Universelle; Photo: ©Saint-Gobain; Right: Atelier le Moletoir de la Glacerie in Chantereine, 1934; Photo: ©Saint-Gobain

Left: Villa Tugendhat, Brno 1928; Architect: Ludwig Mies an der Rohe, Chicago; Photo: ©Ben Skála, Brno/Wikimedia Commons; Right: Neue Nationalgalerie, Berlin 1968; Architect: Ludwig Mies an der Rohe, Chicago; Photo: ©Deror Avi, Berlin/Wikimedia Commons

Left: Maison de la Radio, Paris 1963; Architect: Henry Bernard, Paris; Photo: ©HZ/Wikimedia Commons; Right: UN Building E, Geneva; Architect: Eugène Beaudoin, Jacques Carlu, Paris; Pier Luigi Nervi, Carlo Broggi, Rome; Sir Basil Spence, Edinburgh; Photo: ©Mourad Ben Abdallah, Geneva/Wikimedia Commons

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Advancing Technology: Saint Gobain

GETAZ – Exhibition Center for Building Materials, Etoy, 2009; Architect: Alain Porta, Lausanne + Wurlod Architects, Pully; Photo: ©Mint Architecture modernism and its desire to open up walls by maximizing any interaction between inside and outside rather than having a balcony or an oriel. Ludwig Mies van der Rohe used 5-metre-long SAINT-GOBAIN glass panes in his architectural icon Villa Tugendhat in Brno, Czech Republic, at the end of the 1920s to implement the basic idea of maximum transparency and utmost usage of daylight. And in 1968, SAINT‑GOBAIN supplied glass panes with an excess length of 5.60 m x 3.60 m for the Neue Nationalgalerie in Berlin, making it a floating urban art space.

Since then, numerous projects have been realized around the world, such as the 11 metre glass panes for the Maison de la Radio in Paris, France, in 1963, and the 13 metre glass for the UN building E in Geneva, Switzerland, in 1971. Although not having been manufactured with the technical processing possibilities available today, SAINTGOBAIN has set standards in producing and processing oversized glass panes – and continues to do so today having many years of expertise in the field.

building genres like: • Airports • Commercial Buildings and Storefronts • Exhibition and Conference Centers • Hotels and Restaurants • Museums • Office buildings • Residential Buildings • Sporting Facilities

Benefits of Overlength Glass Buildings which showcase overlength glass panes are visually striking. In contemporary architecture, transparent building envelopes have become increasingly popular, and overlength panes effectively support this creative feature, allowing for more complex and creative possibilities for architects. But there is more to it.

Large continuous glass façades offer high transparency while providing optimal levels of natural daylight entering the interior space, proven to improve occupant comfort, wellbeing and productivity.

Designing with large glass panes Overlength glass panes are now available in many formats, offering a vast range of possibilities to designers. Ranging in length up to 18 metres, overlength glass panes meet the same building physics requirements as standard size glass units. No matter what type of glass and glass finish you choose for your building façade, all glass processing techniques can be applied to SAINTGOBAIN overlength sheets, just like the usual smaller panes.

Large format glass panes are desired wherever the goal is to achieve open, airy design with a connection between the interior and exterior environment. The spectrum of applications in construction where this particular glazing is used is dependent on the design intention and caters perfectly to a broad range of

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The Oculus – Metro Station Ground Zero, New York, 2016; Architect: Santiago Calatrava, New York; Photo: ©Adam Gong on Unsplash

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Advancing Technology: Saint Gobain

The Broad Museum Los Angeles 2017; Architect: Diller Scofidio + Renfro, New York; Photo: ©Iwan Baan, Amsterdam

Processability and Performance Regardless of the type of glazing and glass finish selected for the building façade, all types of glass processing techniques can be applied to overlength sheets, just like the typical smaller and standard format panes, with no compromise on performance. The ability to offer a range of coated large format glass panes, up to 18 m in length, is exceptional and highly advantageous. Overlength units with solar control attributes to combat overheating, along with low-e coatings for thermal insulation performance, make SAINT-GOBAIN’s offering truly unique!

As previously mentioned, SAINT-GOBAIN has decades of experience in the production of overlength glazing. This expertise is further highlighted with 8-metre long curved panes by SAINT-GOBAIN Glassolution Glas Döring, Berlin.

Whether talking about glass processors or insulating glass unit manufacturers, logistics specialists or building site handling specialists, SAINT-GOBAIN has access to a worldwide network of skilled and reliable partners.

SAINT-GOBAIN’s overlength panes provide a complete offering in the market of façade glass. Designers are provided with tried-and-tested tools, industry expertise and consulting services adapted for modern glass envelopes. The products cater to all traditional façade

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constructions; mullion and transom façades, system façades, story-high glazing or high gloss glass façades, and both horizontal and vertical installations are feasible.

A complete range of thermal and solar control coatings (PLANITHERM XN and ONE on the one hand and the entire COOL-LITE SKN and XTREME range on the other hand), safety glass and soundproof glass structures are made available, plus the whole spectrum of creative possibilities offered by glass finishing. Experienced partners from all areas: specialist planners, contractors, logisticians to mention a few, can be consulted for insights on the most suited solutions for your projects.

Main Glass Processing Operations include: • • • • • • • • •

Cut to size, improved edgework, smooth ground or polished Drilling of holes Bent or curved glass Heat-Soak toughened safety glass Heat-Strengthened glass Laminated safety glass Laminated glass with colored and decorative interlayers Single or multi-colored digital print Full Surface enameling

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Advancing Technology: Saint Gobain

Bending glass up to 8 metres at the plant SAINT-GOBAIN. Berlin; Photo: ©SAINT-GOBAIN Glassolution Glas Döring, Berlin

Logistics and handling with a customized vehicle Expert logistics planning is imperative to transporting large glass for construction. With SAINT-GOBAIN, transportation and handling of overlength glass is managed in a smooth and secure manner, mastering the challenges of heavy loads and narrow inner-city routes and the complexities of construction sites.

Thus architects and façade consultants can rely on the comprehensive experience of our overlength network and fleet of specially developed and customized trucks designed to accommodate the extra-long glass panes and deliver the overlength product in an efficient and professional manner. Panes of up to 18 metres in length and with weights of up to 7 tonnes can be transported to the desired location in full confidence.

Careful planning and preparation is key. For project success using large span glass, one cannot stress enough the importance of getting all partners involved early on, ensuring the characteristic features of the construction, the detailed planning for the building and any special transport variants, routes or installation techniques required to be integrated into the logistic concept in due time.

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But even when the overlength glass panes are at the proposed building site, the story does not end: how does this glass come to its correct position? Normal cranes come to their limits quite easily and even if the appropriate machinery is present, you require competent people to perform the task; not to say that every project or task differs greatly.

A recently completed project illustrates such a challenge: The St. Jakobshalle in Basel, Switzerland, a sports and event hall from the late 70s that required

Special glass truck loading 18 metres long glass panes at the SAINT-GOBAIN Glass plant in Cologne-Porz, Germany; Photo: ©Olaf Rohl, Aachen

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Advancing Technology: Saint Gobain

For this operation in Tapfheim, the German based company heavydrive supplied two vacuum suction systems to the building plot, attached to a set of special cranes. Thanks to an overhead manipulator, the existing glass panes could be centrally sucked and dug under the 3 m deep façade overhang. The floor inclination of about 15 degrees could be compensated by the heavydrive cranes with its four axes and the three axes of the manipulator. The operator then vacuum-sucked the new overlength triple glass unit produced by Thiele Glas, Wermsdorf, Germany, directly into the transport frame and guided it to the opening. The 3-axis manipulator lifted the triple glazing units under the roof overhang and accurately inserted them into the post-beam construction.

Projects like this prove to be exemplary, and there is no quick and easy ready-made solution to the complexity of dealing with overlength glass. Everything needs to be carefully planned, discussed and evaluated in advance with all stakeholders, and prior to production and assembly. SAINT-GOBAIN’s worldwide network of competent partners guarantees professional handling and makes the planning and construction run more smoothly.

Architects and planners can rely on SAINT-GOBAIN and its partners extensive experience in overlength glass.

Achieve your desired façade using overlength panes, previously only possible with standard smaller units, allowing a complete range of processing and finishing options for innovative, elegant and performant façade design. Think BIG and ask us for the support.

Tricky assembly of triple glass units with solar coating COOL-LITE XTREME 50/22 II at the St. Jakobshalle in Basel, Switzerland; Photo: ©heavydrive, Tapfheim basic refurbishment. After competition in 2013, the first prize was awarded to Berrel Kräutler AG in cooperation with Degelo Architekten AG, Basel. The outstanding canopies characterize the appearance of this structure and thus the challenges of this project: 276 overlength triple glazing units with the solar control coating COOLLITE XTREME 50/22 II and up to 9 metres, each weighing 1.5 tonnes, had to be lifted into a post-beam façade construction under a 3 m deep roof overhang. The assembly had to be carried out on an inclined surface and was even more complicated due to frost temperatures and strong wind.

For more details on SAINT-GOBAIN’s overlength glass, where size AND performance matter! go to: saint-gobain-facade-glass.com/products/overlength-18m

James A. Michener Art Museum Doylestown 2011; Architect: KieranTiberlake Architects, Philadelphia; Photo: ©Michael Moran/OTTO, New York

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Executive Boardroom Commentary • IGS interviews David Patterson

Towards a smart IGS: Make Architects have led the design of some very prestigious universities. Your practice has completed winning projects at the Universities of Oxford, Stratford & Nottingham.

What are the major challenges in designing new universities or redeveloping historic buildings and facilities? Particularly in the education sector, how do you ensure that designs respect the original concept and heritage while bringing them into this modern, smart era?

Teaching and Learning Building

An Inspirational

D.P: Yes, we have worked for a number of Universities, including completing multiple buildings for both the University of Oxford and the University of Nottingham across different campuses.

The challenges vary for each University, each has diverse aims and considerations. I would say the overlap is that each wishes to attract and retain the best staff and students by providing the best possible amenities. Academia is now a global market and standing out is much harder and much more important. Each university has its own vision in terms of how it wants to achieve this so understanding and interpreting their vision is one of the first priorities for any design team.

A key approach for us is stakeholder engagement. Again the form this takes varies between each University. At the Teaching and Learning Building in Nottingham we implemented a bespoke stakeholder engagement plan with the client and project manager that involved workshops, interviews and presentations to students, academics, Student Union, Estates and Facilities teams and more. This informed the layout, materials, distribution of uses, and detailed servicing management and maintenance strategies. Our engagement with students was particularly useful in determining what was needed to accommodate different needs, preferences and study styles.

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Executive Boardroom Commentary • IGS interviews David Patterson

campus

IGS interviews David Patterson Lead Project Architect, Make Architects

at Nottingham University

Learning Environment

Our engagement with students was particularly useful in determining what was needed to accommodate different needs, preferences and study styles igsmag.com

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Executive Boardroom Commentary • IGS interviews David Patterson

Another challenge would be working in close proximity to existing buildings, mature trees and services below ground. A large proportion of University work whether new build or redevelopment is on an existing campus with existing buildings, landscaping and services that need to be considered and included in the design. The Teaching and Learning Building is at the heart of one of the largest and most beautiful campuses in the UK with a number of mature trees in close proximity and two heritage buildings. We had to respond to the diverse scale and massing of these buildings and establish a relationship with the beautiful campus landscape.

We also have to consider the campus as a whole, the wider teaching accommodation, halls of residence, amenities and circulation, that the new buildings will work and enhance the wider context not act as individual silos.

IGS: The Teaching and Learning Building at the University of Nottingham was recently added to MAKE’s “academic” portfolio. The latest addition forms part of the 2014-2020 Capital Strategy Programme adopted by the University. It is clear the students are happy here, in particular, the sense of wellbeing can be attributed to the natural light that resonates throughout the building. The students say they prefer to use this space to study and revise rather than in the library.

From your perspective, what are the most important factors and features of the Teaching and Learning Building?

Teaching & Learning - (c) Martine Hamilton Knight

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D.P: The University of Nottingham was looking for a flagship building that would make a clear statement of excellence in education and place students at the centre of a creative collaborative community. The Teaching and Learning Building has been designed to provide a seamless transition between working, learning and socialising, to enhance the student experience as part of the University’s Global Vision 2020.

The building provides a much-needed focal point for the campus and a welcoming nexus for students as they move across the University’s new Learning Quarter. After studying the University’s Learning Quarter masterplan, we identified principal pedestrian routes adjacent to the site and connected them to the building to maximise permeability and provide accessibility from 360 degrees. These routes – which include

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Executive Boardroom Commentary • IGS interviews David Patterson

Teaching & Learning - (c) Martine Hamilton Knight

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Executive Boardroom Commentary • IGS interviews David Patterson

the campus’s primary route, linked to two main entrances – converge within the building to form a top-lit atrium. This layout is designed to respond efficiently to the changing needs of students and teachers alike.

Inside are a number of double-height spaces filled with natural light and made of warm materials like architectural masonry. Views to the surrounding campus landscape ensure the building sits well within its setting; many spaces make use of glazing to blur the boundary between inside and outside.

The building provides new learning and social spaces that promote a strong sense of community and foster a creative environment for students and teachers. There is ample spaces for students to meet and socialise, arranged around seminar and study rooms, a lecture theatre, and a performing arts space.

We provided a flexible framework for change through column-free floorplates which can be reconfigured in a variety of ways simply by adding or removing internal partitions; generous breakout areas with multiple functions; and movable furniture that lets students and teachers define their own interactive spaces.

IGS:. Did the criteria and requirements you had to follow while designing this learning hub change much in the decade since your initial involvement with Nottingham University? We are particularly interested in the changing landscape, concepts of modern design, use of building materials and sustainability?

D.P: What is interesting is that the primary aims of the University haven’t changed greatly since we began working for them back in 2005. They always target a high level of sustainability – usually BREEAM Excellent or above, this means taking a number of factors into consideration, not bolt on measures, but integrated into the very fabric of the building. At the TLB, we reduced its embodied carbon by designing the building to have a 60-plus-year life, using our bespoke green specification to responsibly source materials, and specifying high thermal mass materials such as CLT and concrete planks to regulate temperature. We used self-finished materials such as CLT, and eliminated additional finishes such as drying and painting to reduce VOCs. We led detailed stakeholder engagements to get the balance right between high

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Executive Boardroom Commentary • IGS interviews David Patterson

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Executive Boardroom Commentary • IGS interviews David Patterson

environmental performance and good daylight levels, thermal comfort and ease of use. Our design approach included developing a highperformance facade that carefully balances the glazing-to-solid ratio, minimising glare by recessing windows into the facade, and providing opening vents that passively ventilate the building. We also reduced energy use by designing robust, flexible spaces that can adapt as needs change. We offset our on-site carbon through site renewables such as photovoltaic arrays located on the roof. TLB has recently received an RIBA Award for Sustainability.

The University also prioritises value for money, looking to maximise their return on investment and create buildings that stand the test of time.

The TLB was all about developing an adaptable building that was flexible in both the long and short term and could accommodate as many different learning styles as possible. In recent years there has been a greater emphasis on student experience, flexibility and buildings which are simple to use and operate.

I’d say the University definitely aspires to deliver distinctive buildings which have a unique identity to help them stand out in a global market. The Jubilee Campus is a worldclass centre of research, study, business and leisure where we were asked to design several new spaces that would expand the campus’s facilities and serve as a dramatic focal point for the whole site. At the University’s Sutton Bonington Campus, we delivered a visionary environmentally friendly design for an agricultural research building – using the University’s own straw in an external curtain wall system, the largest of its kind in the UK at the time. And now on the main City campus, we have delivered TLB, at the heart of the campus which is a flagship learning space for the University as a whole.

Architect: MAKE ARCHITECTS Structural Engineer: AKT II MEP Engineers: MAX FORDHAM Contractor: KIER Project Management: GLEEDS Cost Consultant: AECOM Photo Credits: (c) Martine Hamilton Knight

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Executive Boardroom Commentary • IGS interviews David Patterson

Pictures: Teaching & Learning - (c) Martine Hamilton Knight

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD

Building Sky View Agnes Koltay, Koltay Facades

Photo 1 – Sky View overlook

Sky View is a twin tower development with skybridge and skywalk observation deck located in Downtown Dubai, close walking distance from Burj Khalifa. The concept was initiated in 2008 but intense design work commenced only in late 2013, with site woks starting in early 2015. The building is scheduled to be handed over by end of 2019.

The towers are 61 and 57 floor in height, reaching 264 meters. The skybridge is located at floors 51-54, and the skywalk tourist feature at floor 53-54. The development includes 5star hotel rooms (Address Hotel brand), serviced hotel apartments, Skycollection penthouse residential units, food and beverage outlets, select retail space, tourist attractions and rooftop bar with dedicated elevator link.

Sky View is developed by Emaar. The design architect was SOM from Chicago, the lead consultant is Norr Group.

Koltay Facades provided façade engineering consultancy and façade access strategy consultancy from the early design stages to handover. Structural engineering and MEP also by Norr Group. The main contractor is ACC –

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Arabian Construction Company, while the façade package was shared in between Folcra Beach and Al Ghurair Aluminium, with a number of further specialist companies and cladding subcontractors involved. The tensioned glass walls were built by Novum Structures. The tower glass is SS 20, supplied by Guardian Glass, the stainless steel cladding is 6WL from Rimex. The system profiles are supplied by Technal, specifically developed for this project. The BMU system is supplied by Cox Gomyl.

As for each consultancy project, we started with categorizing the façade systems for easy reference. It is advisable to use similarities for grouping in order to avoid too many system types, and usually 4-8 systems should cover a tower. For Sky View, while we had only 7 system types and 2 balustrade types for the towers, additional 11 façade system types and 2 balustrade types were used to describe the entire development including the skywalk, the pavilions, the podium.

Value engineering is often taken as a simple cost reduction exercise executed at the very end of the design stage

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD

Image 1. Setting out comparison of the projects. This generally results into unpleasant compromise on the building aesthetics, with eliminated decorative features, simplified geometry, substitute materials and similar. It is utterly important that cost efficiency items are considered throughout the design process, to bring the resulting tender design within budget.

The first of many of those cost efficiency improvements is an assessment of the geometry and modulation. For Sky View, the original architectural floorplan geometry required 14 different extrusions, considering that malefemale unitized extrusions can take up as much as 2.5 degrees angular change. By altering the merging points of arcs, slightly changing radiuses and amending the modulation, the final solution looks almost identical to the original outline, but requires only 10 different mullion extrusions.

An other important optimization exercise to analyze the wind tunnel test results and translate it to the most optimal framing member sizes and glass thicknesses.

While for mullions a typical value could be selected with local reinforcing or additional bracketing at local high pressure spots, glass is usually designed for the highest pressure, to provide visual uniformity all over the project.

For Sky View however, the glazing thickness was primarily driven by acoustic requirements, and glass thicknesses optimized for that. The planar step of different assembly types can be offset by varied air gap size, adaptor profiles or special mullions. At this stage of the design, the clad-

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Image 2. Wind Tunnel Test ding zones (distance from external side of glass to edge of concrete slab) were finalized and the required slab outline communicated to the structural engineer.

The typical tower system is pressure equalized male – female unitized system, with solid stainless steel sheet infill elements and glazing. The implemented system design had high level of similarity to our tendered design. The balcony doors are outward opening side hinged doors, to enable facetation as the building geometry requires. The door frames are externally concealed by flush glazing, the door hardware is drilled through the glazing. However,

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD

Image 3. inward opening door detail from Koltay Facades Design Intent drawings

some doors are located at very narrow parts of the uneven width balconies, and had to be inward opening. This brought a challenge to system design, where flush glazed concealed frame, high level of watertightness and inward operation was simultaneously required. The implemented solution is less integrated to the fixed frames as intended, but still have relatively slim appearance.

The top few floors of each tower give visual continuation of the towers above the skybridge levels. However, the floor plate outline changes and each floor has a different geometry. Maintaining the unitized system here is impractical, as the new geometry would necessitate additional extrusions to deal with tighter radiuses. Furthermore, the area is easily accessible from the skybridge roof level, via scaffolding. These top floors are more like “pavilions in the sky”. These structures were clad with stick system curtain walling, while maintaining the visual match to the tower areas below.

Image 4. Patch fitted tensioned cable lobby glass wall detail

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There are two main areas of the building with patch fitted glass wall. The panoramic elevator shaft is installed over architectural steelwork, while the two elevations of the ground level lobby are installed over a one -way tensioned cable net. With those cables spanning almost 20 meters, the reaction forces on both sides are large.

These needed to be precalculated and coordinated with the structural engineer to ensure that they are accommodated by the interfacing main structure.

The skywalk area is a giant steel truss itself, with glazing on all sides. The perimeters of the floor area are solid filled, just to cater for a wider audience – some may feel discomfort with fully glazed floor area. The floor glazing has high level of redundancy, consisting of 5 layers of glass laminated with SGP in an IGU assembly. The double glazing improves thermal performance and reduces cooling loads, as well as ensures clear view with no condensation even on those days when the outside air temperature drops below dew point and humidity is high.

The skybridge itself has a 3 story tall trusswork primary structure that was assembled on ground and elevated in position by hydraulic jacks. The main, 80 meters long portion of the bridge was a single 165 tonnes lifting operation over about a week time. The bridge will house residential units and have an infinity pool on top. The bottom side of the bridge is clad with solid stainless steel sheets.

During a late design review, just after procurement of the façade package had started, further decorative flying beam features were added to the building. These give the appearance of certain spandrel zones departing from the tower to smooth the visual transition towards the skybridge and skywalk. While architecturally well placed, the late change introduced complexity on the façade access

Image 5. BMU machine at level 50

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD strategy, by blocking access of the intended BMU machines to the areas below the fly beam features. This necessitated modification of the strategy and further BMU units and accessories. The dense bridge truss limited the overall sizes of the BMU machines placed at level 50, below the bridge belly. The machine and its counterweight could not increase further, however the added extendable pentograph cradle that was needed to reach below the fly beam features necessitated further measures of stabilizing. The machine track was then brought closer to the facades to reduce reach, by rearranging the layout.

An other interesting area for cleaning and maintenance access is the skywalk. The bottom side is reached by monorail system. The sides have an 800 mm external walkway with upper rail for safety and for spare glass manipulation. The roof glass is walkable or cleaning. For reglazing, a small custom built sliding gantry is provided that needs to be assembled and after use disassembled and stored away.

This gives a brief introduction of Sky View’s façade package design and procurement process. The building will soon be ready to welcome visitors as a highlight of Dubai Downtown.

Photo 2. Sky View overlook

Photo 3. Flying beam installation below the skybridge area

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Agnes Koltay – Biography Agnes has MSc in Architecture and MSc in Façade Engineering. Her keen interest in high-rise engineering and glass design lead her around the world. She worked with award winning architects and multidisciplinary global engineering firms prior to founding Koltay Facades in 2011 in Dubai. The company specializes in façade engineering consultancy and work on worldwide projects from their Dubai and Singapore offices. Projects include high-end high-rise buildings around Burj Khalifa area such as Burj Vista, Sky View, Fountainviews, complex shaped buildings such as Museum of The Future and The Opus, and landmark projects such as MOL Tower in Budapest.

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD

Curved Glass: Reshaping architectural glass with new possibilities and frontiers Abstract Curved glass has been in use for many decades.

Modern architecture, incorporating more glass and organic forms, is always pushing the limits of what can be accomplished. New technological advances in glass have taken curved glass fabrication to different levels of complexity and performance in the last few years, and design continues to drive into new frontiers.

Keeping up with the most modern aesthetics, structural, safety, and performance requirements has been very challenging when it comes to curved glass. However, the new architecture movement continues to demand glass with forms and shapes, therefore generating an increase in architectural curved glass structures. The following showcased projects demonstrate examples of how it is possible to accomplish complex curved glass applications when on the front-end manufacturers, fabricators, glaziers, and especially, the design team work in coordination to research materials and the best possible design solutions.

Introduction In recent years modern building architecture has been designed around diverse stringent performance needs.

Some of these buildings have required greater advances in glass to meet such criteria, which have been curved glass. With new fabrication technologies and a broader range of low emissivity coatings availability in the market, exists a window of opportunity to facilitate the architectural intent of having organic shapes, curved features, or dimensional façade skins. The key to success with these types of unique projects is collaboration amongst the design, building, and manufacturing teams. The following are examples presented in further detail.

Corporate Headquarters Facets of a diamond or slices of pizza in Glass?

The façade of a newly constructed Headquarters building in Detroit, Michigan was designed to create the facets of a diamond. To achieve the large diamond facet formation the architects desired, the glass would require a nine (9.0) meter height and split into large triangular forms. The glass required a very tight curve radius and two flat legs as shown in the drawing below (Fig. 1). This type of curve in a triangular shape, created a stunning constellation of diamond facets or subsequently individual slices of savory pizza folded to a structural shape that allows one to easily hold and fold this Italian delight.. Please see below the shape and curve profile for a better understanding:

Fig 1. Corporate HQ Glass Make-Up

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD

Fig 2. Superimposing of Curves Such an all glass “textured” façade installation in Detroit see if better results could be accomplished. After a numrequired to have certain thermal and solar values specific ber of experimental runs, the hard-coated Low E tested to its northern territory. Accomplishing these stringent demonstrated consistent results using the 16” radius and values required glass compositions with the use of the suggestion to modify the radius was proposed to the coatings. It is known in the industry that glass coatings, design team, as seen in the photos below (Photos 1 & 2). predominantly Low E coatings, do not withstand tight The low E coating utilized during the successful triradii bends. Offering solutions in the interest of archials, Energy Advantage from Pilkington, is very clear and tectural design, the curved glass fabricator developed neutral in color, and while it does not offer the best solar numerous configurations and trials over a six (6) month performance, it helps lower the U-value of laminated period in order to fabricate the ideal glass make up with glass, from 1.01 to 0.72 BTU. To accomplish better solar the greatest visible light transmission, the most neutral performance and the curve requirement, the curved glass color appearance, the best possible solar and thermal performance, and specifically, consistent quality results given the use of coatings.

Various coatings were tested using the required radius, including hard coatings, and coating damage was visible after the trial runs.

Understanding the design intent, the geometry proposed, and the fabrication challenges, the curved glass fabricator´s technical team laid out different curve profiles per the drawing above (Fig. 2), where the radius could be larger in order to decrease the stress on the coating and the design intent would still be achievable. While the radius seemed to have a large change, from 8” to 16”, the difference in geometry did not present any major change to the design intent.

The curved glass fabricator ran internal trials with the new radius to Photos 1 & 2. Full Size Mock Up Viewing

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD

Table 1. Corporate HQ Performance Chart

fabricator used an XIR® film interlayer by Eastman which enabled the glass to be highly transparent, very neutral in appearance, and achieve the solar performance shown in the chart above.

The glass installation details consisted of only top and bottom structural supports, and the vertical edges were butt glazed, circumventing the visual obstruction of vertical structural elements. The shape and radius required the glass to be annealed. Taking these two (2) elements into consideration, it was critical that the interlayer offered additional structural support and compatible with the film interlayer. Eastman’s DG41 was selected to add structural strength and compatibility with the XIR® interlayer that offered solar performance.

Production of the one hundred and two (102) panels was completed in the time required, and the results obtained in the initial trials were consistent throughout the manufacturing process. To assist the installation process, heavy duty custom metal profiles were shaped and shipped to the curved glass fabricator to be glazed. The structural performance required a 4 1/2” thick layer of silicone that had to be applied following strict quality guidelines and complexity per the figures below (Fig. 3).

Performing the glass to metal assembly process in the same factory where the glass was curved, insured that all lites perfectly aligned with the shape of the metal structure and simplified glazing the façade.

Fig 3. Custom Metal Glazed Profile

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Photo 3. Glass inspection The design and building team visited the curved glass fabricator facility to review the manufacturing process and participated in the inspection of 100% of the units.

The fabrication of this project exemplifies the strict design requirements demanded from glass in modern architecture and in parallel has to meet safety and thermal milestones. The process of curved glass adds many variables and complexities to coatings and interlayers available, and poses installation challenges. However, through extensive pre-project research and development, and construction joint efforts, most of the obstacles can be overcome proposing many different products available today worldwide and occasionally conceding on the initial design proposed.

Curved manufacturing techniques and knowhow can make some of the most paramount architectural designs possible.

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Photo 4. Glass “ izza Slices” University of Iowa Stead Family Children’s Hospital Shielding a healing atmosphere with Tornado resistant glass This particular building designed by Foster and Partners is a Children’s Hospital in Iowa City, Iowa. The end client sought to offer a safe surrounding for the patients and families within the walls of the curvilinear healthcare facility with enhanced protection during severe weather conditions specifically tornados. Testing to find the precise glass formulation to withstand a tornado required

Photo 5. Corporate HQ Installation Progress a significant amount of time and extensive research, in addition to a strong collaboration between the client, interlayer manufacturer (Kuraray), and curved glass fabricator. Different glass configurations were tested at a certified laboratory to withstand impact and high wind speeds. Once the specific glass construction that met the safety and resistance requirements was determined, it all came down to the fabrication and logistics of the glass scope (Fig. 4).

One of the initial challenges in the fabrication of the curved glass was the secondary sealant requirement of 2” depth in order to withstand the strength of a tornado.

Fig 4. UICH, Glass Make-Up

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Photos 6 & 7: UICH, Glass Inspection

Table 2. University of Iowa Children’s Hospital Performance Chart

Photo 8. UICH, Crating Photo 9: UICH, Podium

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Photo 9. UICH, Podium

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD Both curved and flat glass with such a deep silicone infill entail special tooling equipment capable of injecting an impacting amount of silicone. Consequently, this technique required additional exploration and investment that through the joint works of the glazier contractor and building team was possible to accomplish.

The design and building team reviewed and inspected a number of mock ups to determine the best glass make up that met the safety, structural, and aesthetics requirements. This process was significant in securing the success of the execution of the job.

The glass manufactured for the windows is not only large in format measuring at 141” x 90” and able to withstand a tornado, but it also meets energy code. The combination of glass size, volume, quality, performance, flat and curved, and tornado safety requirements posed a great glass fabrication challenge. The importance of having a very close collaboration between the building owner, the design team, the glazing contractor, and the glass fabricator, enabled this intricate project that had very complex glass make-ups, to be executed on time and seamlessly.

Conclusion.

There are many existing projects beyond the two prime showcases discussed in this paper where performance and aesthetics have played equal principal roles with curved glass applications. The design and performance possibilities that curved glass offers architects and building users is very extensive. Curved glass is not a simple product to manufacture; advanced technology combined with in-depth know how is essential to solve many special design features. A fundamental element in achieving success with these one-of-a-kind curved glass creations is time allowance to develop the correct glass configurations that can solely derive from close partnerships between project key players. An extended development process may be necessary in order to achieve a well-executed project and as a result, a collaborative effort initiated at the design stage between the architectural team, the curved glass manufacturer, the glazing contractor, and even other manufacturers of key components such as interlayers or coatings are essential to shaping the footprint into new architectural frontiers with curved glass.

Photo 10. UICH, Installation

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Mistral Tower:

Fig. 1 – Mistral Tower.

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Solutions for SSG Joint Optimization in Cold Bent Units Viviana Nardini, Sika Services AG, Tueffenwies 16, CH8048 Zurich – Switzerland (nardini.viviana@ch.sika.com) Jonas Hilcken, TU Darmstadt – Institute for Structural Mechanics and Design, Franziska‐Braun‐Straße 3, 64287 Darmstadt – Germany (hilcken@ismd.tu-darmstadt.de) Abstract Use of cold-bent and warped glass units in unitized curtain walling is a state-of-the art application.

During the last years, such a global trend has challenged the design and engineering of glass units, frame elements as well as bonding joints in Structural Sealant Glazing (SSG) applications and has pushed for the investigation of material performance and calculation concepts, beyond available standards and guidelines.

With reference to SSG joints, investigation has focused on proposing simplified equations to evaluate cold bending stress and studying relaxation and creeping behavior of silicone adhesives to exploit material performance beyond standard limits. Such investigation process allows identifying where opportunities for systems optimizations are and clarifies that effective coldbending solutions cannot be uncoupled from new principles of system design, premanufacturing and installation.

The development of Mistral Tower in Izmir offers the chance to evaluate in detail the impact of different frame solutions in combination with different production and installation methods and is used to present to system designers and façade producers valuable options and guidelines for approaching design of SSG cold-bent units effectively.

1 Mistral Office Tower Mistral Izmir is a prestigious project in Izmir (Turkey) designed in 2011 by Progetto CMR – Massimo Roj Architects and consisting of a Residential Tower and an Office Tower connected by a Shopping Center (Fig. 1), which are landmarks of the city skyline thanks to their architectural shape and height.

This paper focuses on the design of the cold-bent glass façade of the Office Tower, a 46-floor 180m-high building closed by a double skin façade.

The variable layout of the building slabs rotating at each floor level (Fig. 2 and Fig. 3) posed immediately the challenge for the design of a cost-effective solution for the outer glass skin. Advanced parameterization analysis for façade optimization allowed identifying in a cold-bending solution the optimum way to proceed: by use of slight curvatures, a single rectangular façade element to cold-bend up to the required level could be designed to develop the entire building façade.

As in the majority of international projects where complex geometry and sophisticated layouts want to be emphasized by flawless surfaces and transparency, fixing

Fig. 2 – Slab layout (Floor 2) ®.

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Fig. 3 – Slab layout (Floor 20) ®.

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD of cold-formed glass panels by Structural Sealant Glazing (SSG) systems was the target – with the structural silicone adhesives having the function of ensuring a durable loadbearing connection between frame and glass units.

2 System Details and Boundary Conditions Typical elements of the outer skin facade consist of a rectangular insulating glazed unit 1528 mm x 4000 mm (width x height), composed by two laminated glass panes 8 mm thick (outer side) and a monolithic glass pane 8 mm thick (inner side) spaced by a cavity 16 mm deep. In order to maximize transparency, solution with IG units bonded

by Sikasil® SG-500 structural silicone to aluminium profiles along all four sides was designed.

Following boundary conditions apply for the system design: • The dead load of all glass panes is permanently supported mechanically; • The façade components are required to withstand a typical wind load of 2.50 kPa, reaching maximum values up to 4.0 kPa in local areas of the Tower; • Maximum temperatures expected for glass panels and aluminium frames during service life are 80 °C and 55 °C respectively, according to [1].

• A maximum out-of-plane displacement of +32 mm or -32 mm needs to be imposed at one of the top corners of each façade element by cold-bending.

FE analysis allows to evaluate the magnitude of the loads to apply at the top corner of the elements to coldbend them up to the required level (Fig. 4). The analysis takes into consideration the effective IGU geometry, glass composition, properties of glass interlayers and stiffness of the IG edge sealing system.

Ftot = 310 N Force to cold-bend the IG unit (short-term analysis) Ftot = 120 N Force to cold-bend the IG unit (long-term analysis) Fout = 220 N Force to cold-bend the outer glass pane (short-term analysis) Fout = 60 N Force to cold-bend the outer glass pane (long-term analysis)

3 Initial Design The initial design of the façade elements included flat aluminium profiles 185 mm deep bonded to flat glass units (Fig. 5). The idea was to assemble and install each element as follows: • The flat IG unit is properly positioned on spacer tapes applied on the flat aluminium frame; • The gap between frame and glass is filled in by Sikasil® SG-500 silicone; • When the joints are fully cured, the bonded assembly is moved to site; • On site, an out-of-plane displacement of 32 mm is imposed by cold-bending at one of the corner of the bonded assembly, to shape and install it.

Described cold-bending procedure introduces into the SG joints [2]: • Permanent tensile forces Ftot (Fig. 4) caused by restoring of back-flipping forces of displacements elastically imposed to flat units; • Permanent shear movements sjoint (Fig. 4) due to differential displacements between bonded surfaces, imposed by rotations due to cold-bending.

Based on the initial system designed, Equation 1 allows to calculate [2] that a shear differential displacement sjoint = 3.2 mm needs to be accommodated by the SG joints due to cold-bending.

Fig. 4 – Forces, displacements and deformed joints after a flat bonded assembly is cold bent ®.

Fig. 5 – Initial system design ®.

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD Based on such displacement, Equation 3 allows to calculate that a minimum thickness of 51 mm would be required for the SG joint. The value is obtained considering that shear performance of Sikasil® SG-500 are exploited above typical limits set by standards [1] up to a strength value of τ∞,Relax = 0.0315 MPa, which takes into account for adhesive relaxation phenomena under permanent and limited deformation [2].

It is immediately clear that required SG joint thickness is unreasonable and opportunities for joint optimization need to be found.

4 SSG Joint Optimization by Frame Design Equation 1 clarifies that the distance between barycentre of the bonded cross sections (defining the position of bending axis) plays a major role in defining the magnitude of the differential displacement sjoint to be accommodated by the joints; with regard to this, the cross sectional depth of the aluminium profile has for sure the higher influence. Thus, reducing the depth of the bonded profile offers immediately the opportunity to reduce significantly the minimum SG joint thickness.

Based on such considerations a second façade system was developed and evaluated, including IG units bonded to slim aluminium adapter profiles 6 mm deep. Compared to assembly method of Section 3 (Fig. 5), the idea was to assemble and install each element as follows: • On factory, the flat IG unit is preliminary bonded to the slim aluminum frame by structural silicone Sikasil® SG500; • When the joints are fully cured, the bonded assembly is cold bent up to the required level and mechanically fixed to load-bearing profiles either on factory or on site.

The new design approach allows for a massive joint thickness reduction down to 6 mm by Sikasil® SG-500, due to the cold-bending differential displacement highly reduced to sjoint = 0.24 mm. Considering all loads involved during system service life (Section 2) and wind loads of 2.50 kPa, a minimum SG joint dimensions of

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25 mm x 8 mm (bite x thickness) by Sikasil® SG-500 is required.

It has to be noted that in cold bent systems using a slim profile is valuable if it is ensured that it is free to slide and rotate around its barycentre during the cold bending phase. In other words, it does not make sense to fix mechanically the flat assembly to the main load-bearing frame if it is not cold bent yet. As a consequence, first manufacturing and installation option relied on: • Bonding the flat slim profile to the flat IG unit on factory and moving the assembly on site when joints are fully cured, • Cold bending such assembly on site, • Fix it mechanically to the main load-bearing frame already installed on the main building structure.

Anyway, if one considers that reducing the bonded profile cross section has only the target to minimize the distance between component bending axis, it is clear that system manufacturing and installation can be simplified by designing a mechanical connection between main profile and slim profile that can ensure free sliding of the slim profile with regard to the load bearing frame.

As a consequence, the use of a slim adapter frame bonded to the glass unit and free to slide into load-bearing frame (Fig. 6) represents a basic requirement to limit cold bending effects on SG joints, while minimizing production and installation efforts. On factory, the flat slim adapter frame already inserted into the main frame can be bonded to the flat IG unit; after joints are completely cured, the assembly can be moved and cold-bent on site for installation.

Fig. 6 – Slim adapter frame free to rotate and slide ®.

5 SSG Joint Optimization by Manufacturing Method Additional options for actively influencing the magnitude of shear movements sjoint in the SG joints exist also by implementing different cold-bending procedures.

A very effective way to null completely the permanent shear stress in the SG joint due to cold bending is using hot-bent frame members, so that only the flat IG unit needs to be cold bent. Independently from the cross-

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD sectional depth of the frame profile, the glass unit can be cold-bent on the pre-shaped frame and temporarily fix to it by mechanical devices; application of the SG joint can follow. After the adhesive has completely cured, mechanical devices can be removed. As result, tensile forces will stress the joints but introduction of permanent shear stress due to cold bending will be prevented permanently (Fig. 7).

Based on façade configuration and loads involved during service life (Section 2), such manufacturing procedure allows reducing SG joint dimensions of Sikasil® SG-500 to 18 mm x 8 mm, considering a maximum wind load of 2.50 kPa.

Fig. 7 – Forces and deformed joints bonding after the frame and the glass are shaped ®.

6 SSG Joint Optimization by Installation Method A valuable option to limit the permanent shear stress in the SG joints due to cold bending is to temporary fix the cold bent IG unit by mechanical devices to a cold bent frame; after that, application of the adhesive can follow. When adhesive is fully cured mechanical devices can be removed.

At this stage, shear stress due to elastic back flipping displacements between bonded parts will cause shear stress into the SG joint. Anyway, such assembly will have to be transported to site and there cold-bent again for installation. That means that duration of cold-bending shear stress will be limited only to the timeframe from production (removal of temporary fixing between deformed IG unit and frame) to installation.

It is immediately clear that criteria for controlling such timeframe exist in order to minimize cold-bending effects on SG joints: • The shorter the timeframe, the shorter the shear stress duration and the lower the impact on SG joint dimensions (the higher the adhesive shear strength offered) • The lower the temperatures arising on frame and glass during such timeframe, the lower the simultaneous differential displacements occurring between bonded parts due to thermal dilatations.

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In Mistral Tower system, implementing the described installation and cold-bending procedure could allow reducing the SG joints dimensions to minimum 18 mm x 8 mm by use of frame 185 mm deep; this considering a maximum temperature of 50 °C for frame and glass and ensuring elements stored in horizontal position in the timeframe from removal of temporary fixings to installation. Such timeframe had to be limited to maximum 7 days.

7 SSG Joint Optimization by Combined Methods Cold-bending procedure described in Section 6 combined with frame design consideration provided in Section 4 gives the chance to reduce further the SSG joint dimensions.

As temporary shear displacements are introduced into the joints due to cold bending, it is obvious that cross sectional depth of the bonded profile has an impact on SG joint dimensions. Of course, the shorter the displacement duration, the lower the impact of cross sectional depth on joints.

Considering same conditions and cold-bending procedure mentioned in Section 6 but including a slideable adapter frame 6 mm thick, SG joint by Sikasil® SG-500 could be applied according to a minimum dimensions of 21 mm x 7 mm, which minimizes joint thickness.

Opportunities for reducing SG joint bite also exist. A typical strategy is using permanent mechanical devices to restrain the glass unit to the frame (Fig. 8), so that no permanent tensile forces due to cold bending are transferred to the joints. Anyway, using such devices was excluded in Mistral Tower due to the aesthetical impact on the final facade.

System described in Section 6 was finally selected for design and construction of the outer skin façade. Such a method that required strong limitations in transportation time was possible due to the lucky situation where the location of the production factory was very close to the installation site.

Fig. 8 – Forces, displacements and deformed joints after the flat bonded assembly is cold bent and mechanical devices are used ®.

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD 8 Evaluating the influence of the frame cross-sectional depth by FEM analysis To estimate the influence of the frame height on stresses introduced into SG joints, a numerical analysis was performed with the multiphysics finite element code ANSYS (version 18.2). All parts of the façade system (aluminium profiles, glass, interlayer, SG and IG joint) were idealized using volume elements. To estimate the stresses in an appropriate way, isotropic hyperelastic material model for the Sikasil® SG-500 structural silicones was used, as this resembles the stress-strain behaviour in good approximation [3] [4]. The material parameters are given in [5] The following assumptions were made for the Table 1 – Minimum SG joint dimensions required with Sikasil® SG-500 due numerical calculation: cold-bending and all other loads, considering different design, manufacturing • Volume elements Solid 186 for and installation methods and different frame-cross sectional depths. all components: SOLID186 is a higher order 3-D 20-node solid element that exhibits quadratic displacement behaviour • Rectangular cross-section with equivalent bending stiffness to the actual substructure for the aluminium profiles • Brick volume elements with an aspect ratio close to 1 and a meshing size of 4 mm for the relevant SG joints • Polynomial (n = 2) hyperelastic model for the SG joints according to [5] • Linear elastic material behaviour for aluminium, IG joint, glass and PVB interlayer • Bonded contact between SG joint and glass, between SG Fig. 9 – Influence of frame cross-sectional depth in flat assembly cold bent joint and aluminium profile and after the joints are applied ®. between IG joint and glass • Local nodal support at the corners of the supporting frame.

In order to estimate the influence of the frame crossby FEM analysis for very low profile depths results from sectional depth on the stress introduced into the SG joints the decrease in bending stiffness, which was not adjusted due to cold-bending, the profile depth was varied in the fifor this calculation. The results of the numerical simulanite element calculation. Results are plotted in Fig. 9 and tion are qualitatively and quantitatively consistent with compared to the analytical solution of Equation 1. A linear the analytical solution. The analytical solution, however, relationship between the profile height and the resulting slightly overestimates the stress and is therefore on the stress is confirmed. The initial stress increase obtained safe side for the dimensioning.

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD 9 Conclusions The development of Mistral Tower in Izmir offers the chance to evaluate in detail the impact of different frame solutions in combinations with different production and installation methods on SSG joints of coldbent façade elements.

The design of slim adapter frame free to slide into load-bearing frame represents a basic requirement to limit cold bending effects while minimizing production efforts.

Valuable SG joint optimization results can be further achieved if bonding on either pre-shaped (hot-bent) frame or pre-shaped (cold-bent) frame/glass assembly is possible, or if cold-bending stress can be confined to a limited timeframe by a clever production method in controlled conditions.

With reference to the facade system used in Mistral Tower, advanced FEM simulation is implemented to estimate the influence of the cross sectional depth of the bonded profile on the stress in the SG joints. In line with the simplified equations proposed, the analysis confirms that a linear relationship exists between depth of bonded frame and stress on SG joints, proving that the slimmer the bonded frame the smaller the differential displacement imposed to SG joints and the smaller the joint thickness required.

10 References 1.

EOTA ETAG 002-1, Guideline for European Technical Approval for Structural Sealant Glazing Kits (SSGK) – Part 1: Supported and Unsupported Systems (2012).

2. Nardini, V., Doebbel, F.: Structural Silicone Joints in Cold-Bent SSG Units. GPD Glass Performance Days 2017, Complex Geometry, Tampere. pp 23-27.

3. Clifta, C. D., Carbaryb, L. D., Hutleya, P., & Kimberlainc, J. Next generation structural silicone glazing. Journal of Facade Design and Engineering, 2014, Vol. 2, pp 137-161.

4. Staudt, Y. Investigation of the material behavior of glued connections with silicone.

Darmstadt: Master Thesis at Technische Universität Darmstadt, 2013.

5. Sika Technology: Hyperelastic constitutive models for the FE simulation of Sikasil® SG500. 09.09.2013.

Sika Services AG: Additional Technical Information for computer-aided analysis to simulate the joint behavior in façade applications using Sikasil® SG adhesives. 02.02.2017.

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Enhancing the Light - Curved Insulated Glass Unit Design Study Adam Nizich, PE 1, Walter P. Moore & Associates, Inc. Sam Baer 2, Walter P. Moore & Associates, Inc. Silvia Prandelli, Ing. 3, Walter P. Moore & Associates, Inc. Kelly Burkhart 4, Walter P. Moore & Associates, Inc. Keywords: Curved Glass • Insulating Glass Unit • Structural Analysis • Structural Silicone • Facade Abstract Curved insulated glass units formed by tempered bending or annealed slumped bending offer a bold expression of architectural design with transparency and energy efficiency. As more skins with complex geometry are built, design teams need to engage consultants and international industry experts to define the properties and constraints of curved insulated glass units in line with relevant standards and performance. This paper explores the traditional manufacturing capabilities, processes, and further investigates the advantages and structural performance of these glass products. The stiffness gained from curvature in fact presents an opportunity to decrease the visual mass of mullions along straight edges. Thoughtful consideration is also given to address redistributed forces, buckling, and increased effects of climatic loads on a sealed interspace with flexible boundaries. The structural performance and design requirements are compared for insulated glass units with flat, shallow and tight curvature using a comprehensive glass, air, and silicone finite element model. Based on this study, suggestions for specification and analysis of curved insulated glass units is provided.

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Introduction The use of cylindrically curved insulated glass facades has emerged as a novel solution to meet both aesthetic and energy performance objectives. The stiffness gained from curvature has been recognized as a particular advantage over flat glass, decreasing support requirements and improving sightlines, or increasing spans. As a consequence of improved stiffness, curved Insulated Glass Units (IGU) have a reduced ability to equalize internal and atmospheric pressure changes through pillowing compared to flat units.

Knowledge of fabrication capabilities and structural behavior is critical to inform the design of curved glass units. This paper explores the parameters to be considered in the design of a curved IGU and the effects of pressure equalization on cylindrical units by comparing a flat IGU to units with shallow and tight curvature (Figure 1) using a comprehensive glass, gas, and silicone finite element model.

Fig 1. Comparison of IGU curvature in numerical study

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Curved Glass Fabrication and Considerations Cylindrically curved glass for architectural use is formed either by: 1) tempered bending with controlled quenching (fast cooling) to achieve a desired residual compressive surface stress distribution, or 2) slumping over a form followed by annealing (slow cooling) to relax residual stresses.

Tempered bent glass dimensions are restricted by the radius of curvature and size of furnaces available in industry.

Slumped glass can achieve a wider range of geometries, and as a rule of thumb can provide superior optical quality when compatible with strength requirements.

When designing a curved IGU, the following factors should be considered: 1. Coating: When a coating to achieve solar, thermal or aesthetic properties is required, attention should be paid to the type of coating and position of the coating in the IGU. While pyrolytic - ‘hard’ - coatings can be used on both concave and convex surfaces, approved - ‘soft’ - sputter coatings can currently be used on the concave surface without damage from rollers located on the convex surface in tempered bending ovens.

Glass benders continue to investigate new techniques to offer soft coatings on either surface.

2. Glass type: Imperfections may be more visible when clear glass is used in lieu of low-iron with tempered glass compared to annealed or heat strengthened.

Tempered glass is more prone to roller wave distortion on reflective coatings and iridescence (anisotropy) from uneven quenching. Laminated heat strengthened glass can be selected for better visual quality if compatible with the project constraints.

3. Glass thickness: Distortions and tolerances of fabrication will change depending on the type of heat treatment and thickness. Tolerances normally considered on a bent panel include local bow, twist deviations and accuracy of overall bending or deviation from glass thickness.

6. In order to verify the aesthetics of the bespoke glass unit, review of material and progressive visual mockups at each design phase is recommended. The specimen shall be inspected under a diffuse light and not direct sunlight, at a distance greater than 1.5 m.

7. Thermal shock risks: While annealed slumped products are favorable when uncoated glass is used; coated annealed glass is at an elevated risk of breakage from thermal shock.

8. Site breakage: Installation of bent panels shall be studied in detail for compatibility with the glazing system tolerances and deformation. This is to limit additional stresses caused by unintended cold bending by forcing an edge to conform to the tolerances of the framing system.

9. Equalization of IGU cavities: IGU are manufactured with a hermetically sealed gas cavity which are sensitive to pressure changes due to difference in elevation, seasonal fluctuations in climate from barometric pressure, and variations of interspace gas temperature (Figure 3). The ability of an IGU to equalize internal pressures through pillowing is restricted by the stiffness gained through curvature. IGU which restrict equalization can develop extreme internal pressures on glass and seals causing lites to come into contact, resulting in premature failure of seals or glass breakage. Uncertainty exists regarding the proportion of equalization and confined internal design pressure.

The authors have observed that curved IGU are frequently specified on the basis of flat unit structural performance, without consideration of curvature stiffness or equalization. The effects of curvature were compared

4. Radius of bending: Each glass bender has specific manufacturing limitations for the radii, girths and height of rise. It is advisable to confirm the latest requirements with the suppliers in the early phases of the project to understand compatibility of bending methods.

5. Number of glass plies: Laminated heat strengthened glass is also considered in certain cases as an alternative to tempered monolithic panels. Tolerances shall be discussed with the glass bender to assess if the interlayer can bridge the gap between multiple glass layers with different tolerances which can be cumulative.

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Fig 2. Combination of External Lateral Pressures and Internal Pressures on a Curved IGU.

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD with the equivalent flat unit to assess curved IGU performance to enhance designer’s knowledge.

Equalization of IGU - A Comparative Study Seasonal climatic loads generally have limited impact on the efficient design of balanced glass thickness, temper, or dimensions of the secondary seal. Analytical guidance on isochoric actions on IGU are not currently addressed in ASTM [1] or Australian [2] standards.

The effects of elevation change can have a substantial impact on the secondary silicone seal size. Secondary silicone sealant is typically designed for 5% of the transient design capacity for permanent actions. Curved glass fabricators consulted for this study regularly install temporary breather tubes on curved IGU to eliminate elevation effects during transportation to the curtainwall fabricator or site.

The structural performance of a 3.0 m tall by 1.5 m wide rectangular IGU with a 2:1 aspect ratio have been evaluated at flat, shallow (5° to 30°), and tight (60° to 120°) cylindrical curvature. An IGU consisting of symmetric 8mm lites with a 7.7mm minimum thickness [3] with a 16mm air filled interspace was selected on the basis of deflection efficiency for a 2 kPa unfactored wind load representative of high-rise building corners.

It is often possible to reduce or eliminate support at straight edges of curved glass due to stiffness gained from curvature. Rigid support is provided at curved edges, and along all edges of the flat IGU. Flexible support is provided at straight edges of curved glass units that would otherwise deflect more than L/175 for lateral loads

Fig 3. Detail of Finite Element Analysis Model of Curved IGU (IGU curved at 5° to 15° for this study).

Seasonal climatic loads affecting interspace temperature and barometric pressure have been adopted from Table 2, DIN 18008-1 [4]. Change in elevation was reduced to +/- 50 m, respective of the unfavorable seasonal combination, so that edge seals of curved units could be designable for permanent actions. Load actions are summarized in Table 1. Partial load factors and companion load factors found in prEN 16612 [5] for flat units are intended for a reduced consequence class. The authors did not find a lower consequence class appropriate for analysis of glass with stability concerns. For this assessment, partial load and companion factors from DIN 18008-1 [4] are adopted as summarized in Table 2 for use with ULS & SLS load combinations [5].

Table 1. Summary of assumed actions

Table 2. Partial load & companion load factors

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD A geometrically compatible finite element model representing glass, air, and silicone was used for the comparative study of flat and curved IGUs. For practical comparison, simplifications of spacer and edge seal mechanics have been made on the basis that glass does not develop a bending moment at the edges. This assumption is to be considered valid where: a) edge rotations are small, or b) the secondary seal is sufficiently narrow where edge rotations are large.

The Strand7 [6] model was composed of gradually curved QUAD8 plate elements for glass and silicone and HEX20 brick fluid elements representing air (Figure 3).

Subdivision of the plate elements for glass was approximately 50 mm square. A pattern of releases and constraints allowed the fluid to be contained by the bounding perimeter.

The secondary silicone seal for tensile performance was modeled as DOWSIL 3363 with Mooney-Rivlin 2-Parameter Hyperelastic Properties [7], attributed with rotationally released edges. Contact connection elements at the perimeter were representative of the spacer’s compressive properties. The secondary seal was given an increased bite width by adjustment of element thickness.

The initial bite size assumption conservatively restricted elongation, resulting in higher gas pressures, without the need to iterate to optimized design dimensions.

Observations and Results The results of curved IGU analysis fell into two groups: buckling susceptible and stiffness controlled. IGU within the stiffness controlled group exhibited clear trends concerning formed gas pressure, glass stresses, deflection, and edge seal forces. Post-buckled results from IGU curved at 5° to 15° fell outside of these trends due to the snap-through buckling phenomena observed in the analytical models. Due to potential for visual discomfort from excessive deflections, inelastic stress redistribution, and potential damage to seals from twisting, buckling was regarded as a failure as opined by Bensend [8] for buckling of cold bent curved glass. Buckling susceptible units were excluded from the comparison of stiffness controlled units.

Table 3. IGU buckling load. IGU sensitive to buckling below the ULS wind load are identified in red

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Fig 4. Buckling mode of shallow curved glass.

In order to evaluate curved glass buckling capacity, lateral load increments for either wind or isochore pressure were applied to the comprehensive models with appropriate boundary conditions. A geometrically nonlinear static analysis was performed and the resulting force-displacement curves were used to identify the onset of buckling (Table 3) where curvature decreases at the center and a crease forms (Figure 4). To understand if the glass will buckle from a single action, this can be a valuable first step prior to checking all load combinations. The buckling study showed that wind loading applied opposite the direction of curvature led to the onset of buckling at a load less than the ULS design wind load. In addition, the shallow 5° IGU exhibited buckling under isochore pressures.

Loads applied in the same direction as the curvature did not lead to buckling. It should be noted that given the limited number of cases studied in this effort, a sensitivity study on buckling effects is warranted for other IGU sizes or thicknesses.

The formed gas pressure due to unequalized isocore loads in the IGU gas ranged from 0.1 kPa to 5.0 kPa in the summertime and 0.2 kPa to 8.0 kPa in the wintertime for seasonal ULS combinations. The equalization rate of 99% for the flat IGU decreased to 61% for the 120° curved IGU (Figure 5). The resulting isochore pressures exceeded the magnitude of wind.

Flat glass supported on 4 edges developed a stress field located at the center of the pane. With curvature,

Fig 5. Seasonal equalization rate for ULS load combinations

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD peak stress fields were observed to redistribute from the center and concentrate along perimeter regions (Figure 6). Compatibility of curvature with a reduced glass edge capacity and enameled frit is an important consideration during design.

Curved glass that is not susceptible to buckling under design wind loads can frequently be designed as unsupported along straight edges. Support was found not to be required where θ ≥ 30° in the sample set. Deflection

patterns from equalization of isochore pressures were compared with deflection from wind load (Figure 7).

With curvature, the redistribution of forces along the edge seal coincided with the rise of internal pressures. A concentration of edge seal forces was observed on the curved edge. Required secondary silicone seal dimensions are compared in Figure 8. Edge seal requirements [9] due to a permanent +50 m elevation change were determined to be of a similar magnitude.

Fig 6. Above: Tensile stress as result of unequalized isochore pressures. Below: Tensile stress due to wind loads.

Fig 7. Above: Deflection due to equalization of isochore pressures. Below: Deflection due to wind loads.

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Fig 8. Secondary Silicone Seal Bite Requirements for Envelope of SLS Combinations

Conclusion & Summary In conclusion, curvature has been observed to influence fabrication, structural performance, and aesthetic outcomes of IGU. Thoughtful consideration of fabrication capabilities and structural behavior is recommended at early project stages to identify compatible design solutions.

It has been demonstrated by comparison of structural behavior that specification of curved glass on the basis of flat glass design is not appropriate. For example, adoption of shallow curvature to glass can introduce a buckling sensitivity to glass that otherwise had adequate performance when flat.

Adoption of any curvature decreases the IGU’s ability to equalize for changes in elevation and seasonal climatic effects, resulting in unequalized internal pressures that cannot be neglected.

Design standards could benefit from further clarity on the magnitude and combination of isocore effects to stay current with fabrication capabilities and market trends.

A collaborative effort between the owner, designer, and fabricator will help ensure high-performing, reliable, and aesthetically pleasing designs with curved IGU are achieved.

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References [1] ASTM E1300-16, 2016. “Standard Practice for Determining Load Resistance of Glass Buildings,” ASTM International, West Conshohocken, PA. [2] AS 1288-2006 (R2016), 2016. “Glass in buildings - Selection and installation,” Standards Australia, Sydney.

[3] BS EN 572-2:2012, 2012. “Glass in building. Basic soda lime silicate glass products. Float glass,” BSI Standards Limited, The British Standards Institution, London.

[4] DIN 18008-1:2010-12, 2012. “Glass in building - Design and construction rules - Part 1: Terms and general bases, English Translation of DIN 18008-1:2010-12,” Beuth Verlag GmbH. DIN Deutsches Institut für Normung e. V., Berlin.

[5] prEN 16612:2017, 2017. “Glass in building - Determination of the lateral load resistance of glass panels by calculation,” BSI Standards Limited, The British Standards Institution, London.

[6] Strand7, 2019. “Strand7 Finite Element Software”, R3 Preview, Strand7 Pty Limited, Sydney [7] Dow, 2018. “Behavioral Data Sheet. DOWSIL 3363 Insulating Glass Sealant,” The Dow Chemical Company, Form No. 63-6691-01.

[8] Bensend, A. “Beneath the Surface: Buckling of Cold Formed Glass,” Glass Performance Days 2015 Conference Proceedings, pp.

241-246, Glass Performance Days, Tampere, 24-26 June 2015 [9] Dow, 2018. “Declaration of Performance. No SNF_DOP_005,” The Dow Chemical Company, Form No. 62-1886-01 A, Version 3.

Acknowledgements Thank you to the entire Strand7 team, Anne Delvaux with Beaufort Analysis, and the following glass fabricators: Cricursa, Cristacurva, Sedak, and Sunglass.

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Options for Complex Geometry Façades - Single Corner vs.

Free Form Cold-Bending Abstract In the constant search for original designs that truly push the limits, many building projects in the Middle East have been driving global innovation in engineering and façade design.

Not only referring to unreached heights for the world’s tallest building, but also referring to new and unique landmark designs where architects and clients pushed the building industry to develop new, advanced and challenging technologies. One of the current key trends is the request for so called complex geometry façades featuring curved, twisted or even freeform shape façades. These designs often require an early involvement of the façade specialist and the use of advanced computer aided design technologies incl. parametric modelling with script based graphical algorithm editors.

The output of these numerical and graphical computational design processes is used to evaluate the needs for curved or warped façade elements. Referring to warped glass and utilizing the cold-bending technology, being significantly more cost effective compared to the traditional hot-bent glass using slump forms, the two options single corner cold-bending and the free form cold-bending are compared and evaluated on two Middle East projects: The first example is the Shining Towers in Abu Dhabi, conceived as a pair of dancers moving together without touching. The second example is The Opus project in Dubai where the unique appearance of the project was derived from an unusual source of inspiration as the architect sank a hot poker into a cube of ice to create the shape of the irregular, curved void façade.

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Benjamin Beer, Head of Façade, Ramboll, Dubai, United Arab Emirates Introduction The glass cold-bending became an established technology in the façade industry used as an alternative to the costly slump form hot bending of glass. While the structural glass design of cold bent glass panels is relatively straightforward, the setting up of the cold bending limits (warp), the design of the primary seal structural silicone (between aluminium frame and glass) and the secondary seal (edge seal between inner and outer pane of the IGU) still presents a major challenge. This paper focusses on the single corner cold-bending and the recently developed free form cold-bending, giving systematic overviews on the cold bending processes and structural silicone design. Project examples highlighting the two options include the Shining Towers in Abu Dhabi, and The Opus in Business Bay, Dubai. The later represents one of the first façades being built using the new free form cold-bending process in a large scale. An additional item covered in this paper is the comparison and choice of appropriate IGU (insulating glass unit) spacer bars being able to withstand the high shear stresses caused by the cold-bending.

Cold Bending Options: Single Corner Cold-Bending vs. Free Form Cold-Bending Figure 01 provides an overview of the two cold-bending options currently used in façade engineering projects.

The single corner cold-bending is the most common option being realised on various projects over the last approximately 10 years. Various paper covered the principle technology and design methods, see [2], [3], [4] and [5].

Here the aluminium framing members are linear, and the glass is produced flat. For the free form cold-bending geometries including spherical convex, spherical concave, anticlastic free-form, convex free-form and concave / convex free-form, the glass is produced flat and the framing members are curved. Referring to the cold bending distance ‘warp’, the single corner cold-bending only has one warp at one corner – three points define a coplanar surface and therefore only one corner point is warped (point P1, P3, P5 or P7). The edge warp (wp2, wp4, wp6 or wp8) of the two sides adjacent to the warped corner point

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD can be assumed to be approximately half of the corner warp (P1, P3, P5 and P7). For the free form cold-bending, the relation between corner warp and edge warp is more complex. While the corner warp P1, P3, P5 and P7 is usually a positive or negative value depending on a convex or concave cold-bending, the edge warp values wp2, wp4, wp6 or wp8 are smaller in absolute values and could be as low as zero.

Referring to the structural silicone design of cold-bent glass and due to the glass trying to bend back into its original flat position, the elastic cold-bending process causes permanent (long term) tensile stresses in the primary and secondary silicone edge seals. The distribution of the permanent silicone tensile stresses depends on the cold-bending geometry and the method of stress analysis: hand calculations or Finite Element (FE) analysis. Referring to the output of computational FE analysis and stress peaks encountered in the results graphs, the evaluation requires substantial expertise and engineering judgement. The stress peaks are often localized in small areas and might be ‘cut-out’ to avoid an overly conservative design - considering that these small overstressed areas will result in a localised higher elongation, which shall be no problem for the overall system. The concept of corner ‘cut-out’ of local stress peaks was presented for

Fig 01. Comparison single corner cold-bending vs. free form cold-bending, incl. structural silicone stress models

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single corner cold-bending in [2] and further guidance on the durability of the edge seals can be found in [5]. Figure 01 compares the theoretical stress models (e.g. by hand calculations) with actual stress models (FE calculations), both for single corner cold-bending and free form shape cold-bending.

Single Corner Cold-Bending - Shining Towers, Abu Dhabi Conceived as a pair of dancers moving together without touching, the Shining Towers project in Abu Dhabi (see Figure 02 and 03) compromises two multi-storey towers (33 and 42 storeys respectively) that appear to ‘lean’ in two directions, sideways and towers one another. Ramboll was appointed to provide multi-disciplinary services incl. façade engineering. The office tower is a leaning and twisting building standing 34 storeys above the podium, Figure 04 shows the floor slab edges in plan twisting floor by floor over the building’s height.

Fig 02. Shining Towers, Abu Dhabi (Architects: H&H)

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD The unique curving façade provided a challenge to the design team. Through intensive research and development at early stage of the project, followed by third-party testing, the team decided to proceed with double curved cold-bent façades. The façade system utilized the extrusions of a typical unitized façade flat system which is bent post-production on site (see Figure 05) to follow the inclined and twisted façade. Also see Figure 13, Option A: Site cold-bending, post cold-bending. This solution eliminated the need for costly hot-bent curved glass, or an architectural re-design.

During the initial design stages, the question following questions came up: • How to pull the unitized façade panel and what is the force?

• Won’t the glass break due to the cold-bending?

• Won’t the structural silicone tear?

• Won’t the stack joint of the bent unitized panel be impossible to interface with adjacent panels?

Three phases were set up to achieve the required confidence the cold-bent design; • Phase 1: Model verification • Phase 2: Design verification • Phase 3: Durability verification For phase 1, actual units of the unitized façade were produced following the established model with actual aluminium extrusions, glass and details. A certain number of these units were installed on initial resting rigs (see Figure 06) as per site conditions, then one corner pulled up to the maximum design cold bending ‘warp’ and further up to glass failure. Details of this testing can be found in the next chapter. The goal of the testing was the verification of the theoretical assumptions to actual test results.

Fig 03. Shining Towers, Abu Dhabi (Architects: H&H)

Fig 04. Shining Towers, floor plans showing slab edge twisting over the building’s heigh

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Fig 05. Shining Towers, cold-bent façade during construction

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD Single Corner Cold-Bending - Shining Towers, Cold-Bending Testing Mock-Up Intensive mock-up cold-bending testing (see Figure 06) was carried out to determine and verify the accuracy of the structural calculations for the façade system and structural silicone. Measurements included glass stresses for the 30mm thick IGU with 8mm outer and 6mm inner pane in accordance with ASTM E998-05. These stresses were derived by using tri-axial strain gauges to meas-

Fig 06. Shining Towers: Cold-bending test mock-up, coldbending application

ure change in strain and subsequent the stresses in the glass during bending. The structural silicone dimensional changes were measured using digital callipers. For the cold-bending test, a turn-buckle loading mechanism was attached to one corner of the unitized façade panel at bracket location through a load cell. A rigid steel line was installed in parallel to the external glass surface as a reference. Digital callipers (LVDT transducers) were used to measure the dimensional changes, the results from all

Fig 08. Shining Towers: Cold-bending test mock-up, cold-bending application, top view

Fig 07. Shining Towers: Cold-bending test mock-up, cold-bending application, side view

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Fig 09. Shining Towers: Cold-bending test mock-up, ultimate test and glass breakage at 290mm (mock-up 1) and 300mm cold-bending (mock-up 2)

electronic instruments were recorded by computer controlled data logger. Initial bending ‘warp’ was applied at the top corner and then incrementally increased in 5mm steps (see Figure 07 and Figure 08) up to glass failure.

Figure 09 shows the crack origin at centre of the glass edge opposite to the cold-bend ‘warped’ corner, exactly matching the initial FE calculations. The deflections of the framing members, glass surface strain and sealant dimensions were measured at each bending increment.

The initial bending was kept under loading for 48 hours and silicone strains were checked.

Free Form Cold-Bending – The Opus, Dubai The most well-known project example of the new free form cold-bending technology is the Opus project in Dubai (Figure 10). The appearance of the building derives from the architect, world famous Zaha Hadid, sinking a hot poker into a cube of ice to create an irregular, curved void in the middle. Ramboll Façade was appointed for the initial design stages and set up the principle façade types and system approaches (see Figure 11). The pro-

Fig 10. The Opus, Dubai (Architects: Zaha Hadid Architects).

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ject is mixed-use 20 story building with a hotel, serviced apartments and offices. The cube design is intended to float above the ground, featuring the above mentioned freeform void ‘hole’ in its centre to allow for eye-catching views. The sides of the void are formed by two concrete towers set approximately 50 m apart and linked above the void from the 20th floor upwards by a five-storey steel bridge structure.

The external façades use relatively transparent glazing with a partial mirror pattern, in contrast to the freeform void area using dark blue glazing. Glass visual mock-up reviews and initial cold-bending testing was carried out a façade contractor’s factory, see Figure 12. The key feature free form void façade utilizes a combination hot bent glass, single corner cold-bent and free form cold-bent glass. Panel dimensions of the void façade are moderate with approximately 1.50 m x 1.95 m (nominal), 1.90 m x 2.20 m (widest) and 1.52 m x 2.51m (longest).

Due to its shape, the Opus void façade proved to be the most challenging part for the façade designer and contractor. The new technology of free form cold-bent glass was followed to reduce the quantity of hot bent glass and to achieve consequent cost savings. Only for panels where the amount of warp and cold-bending was above predefined limits and deemed excessive, partially spherical double curved hot bent glass was specified and produced using glass processing technology from the automotive industry. The design of the primary and secondary structural silicone seals of the free form cold-bent panels was discussed in [1], including an explanation of the design approach ‘Engineering Stress’ vs. ‘Finite Element Stress’ and handling of stress peaks with ‘cuttingback’ as illustrated in Figure 01.

Different Types of Spacer Bars and Effect on the Shear Stresses due to Cold Bending Figure 13 illustrates a typical IGU under cold-bending deflections highlighting the critical shear stresses in the primary and secondary silicone seals. Detailed information on the design of the structural silicone for single corner cold-bending and free-form cold-bending can be found in [1], [2], [3] and [6]. The illustrations in Figure 13 also show that the shear forces not only affect the primary and secondary seals, but also the IGU spacer bars. Traditionally, the spacer bars are aluminium or stainless steel hollow sections filled desiccant. Obviously, these relatively ‘stiff’ spacer bars have more issues to cope with high shear deflections compared to the recently developed ‘flexible’ spacer bars.

The ability of IGU edge seals and spacer bars to cope with high deflections is not only important for long term cold bending deflections, but also for short term deflections due to wind loads. These short term deflections are usually an issue for façade system with high deflections, e.g. cable façades being subject to relatively high short

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD term edge warp deflections in the IGU’s. The theory behind edge warping of insulating glass units was described in detail in [1]. For both the edge warping deflections and the ‘normal’ mid-span deflection deflections, the edge seal as well as the spacer bar of insulating glass units are

the governing factors for the deflection or (cold-bending) warp limit. Besides the traditional aluminium und stainless steel spacer bars, two relatively new types of spacer bars are available: A) Silicone foam spacers, and B) Thermo plastic spacers (TPS spacers). TPS spacers usually consist of a one component polyisobutylene with included desiccant material. As there is no stiff metal insert (in contrast to aluminium or stainless steel spacers) and the whole spacer is made of a homogeneous, relatively flexible material, these spacers tend to be able to withstand higher deflections of the insulating glass units compared to metal spacer bars.

Figure 14 gives an overview of the different types of spacer bars. Referring to the aluminium and TPS spacer bars, several tests and numerical analysis carried out by the Institute for Lightweight Structures and Conceptual Design (ILEK, University of Stuttgart) were carried out as part of two diploma works, refer to [7] and [8]. These have picked up the problem of edge warping and midspan deflections of insulating glass units.

Figure 15 shows a typical comparison of aluminium and TPS spacers under deflections testing; the ‘flexible’ TPS spacer shows significant lower shear stresses while

Fig 11. The Opus, Dubai. Initial design sketch showing the interface between the vertical façades and the curved void façade/roof glazing

Fig 12. The Opus, Dubai. Early stage visual mock-up for the cold-bent glass

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Fig 13. Shear stresses in structural silicone primary and secondary seals – Single corner cold-bending vs. free form cold-bending

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Fig 14. (above left) Types of spacer bars, ‘stiff’ metal spacers vs. ‘flexible’ spacers. Fig 15. (above right) Test results comparing ‘stiff’ aluminium spacers vs. ‘flexible’ TPS spacers [9], [10] being able to withstand higher elongations – as a consequence to higher deflections of the insulating glass unit. The importance of the spacers and edge seals of insulating glass units is widely known, IGU processors are limiting the amount of stresses in the spacers and edge seals since many years by giving deflection limits for the insulating glass panel. These limits shall guarantee that the edge seals of the insulating glass unit do function

Conclusion & Summary Following the architectural trend pushing for more and more complex façade geometries including two-way curvatures, the single corner cold-bending method represents a less common however over the recent years relatively well researched technology. The paper presents a landmark project in Abu Dhabi where this single corner cold-bending technology was successfully tested and realized. A more novel and advanced approach for even more complex geometry façades is the free form cold-bent glass method, being implemented in a large scale for the first time on The Opus project in Dubai. For both the single corner cold-bending and free form cold-bending approach, the effect of the glass trying to elastically deflect back into its original flat position must be considered. Here, the primary and secondary seal structural silicones and the IGU spacer bars tend to be the weak point and careful design considerations are required as current design standards do not cover these topics. This paper intends to provide guidance including a systematic and in-depth review of the associated issues.

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over a long period of time, keeping in mind that a failure of the edge seals would lead to air and moisture penetration through the seal into the cavity of the insulating glass unit and condensation within the glass unit would occur. In case this happens, a replacement of the insulating glass unit would be required leading to high costs for access to the glass panels, dismounting and installation of the new IGU.

References [1] Beer, B.: Free-Form Shape Cold-Bent Structural Silicone Glazed Façades - Design Concept and Challenges, Glass Performance Days, 2017 [2] Beer, B.: Structural Silicone Sealed Cold-Bent Glass – HighRise Projects Experience Leading to a New Design Concept, Glass Performance Days, 2015 [3] Beer, B.: Complex Geometry Façades – Introducing a New Design Concept for Cold-Bent Glass, Glass Performance Days, 2013 [4] Datsiou, K.C., Overend, M.: The mechanical response of cold bent monolithic glass plates during the bending process, Engineering Structures 117 (2016) 575-590, 2016 [5] Besserud, K.,Bergers, M., J. Black, A., Donald, L. D., Mazurek, A., Misson, D., Rubis, K.: Durability of Cold-Bent Insulating-Glass Units, Journal of ASTM International, Vol.9, No.3, 2012 [6] Dow Technical Information (Ver 1.01, 14.03.2019) version 29/06/2018, Cold Bent Glass in Structural Glazing, Dow Chemical Company [7] Fauth J., Flexibilität des Randverbunds von Isolierglasscheiben, Diplomarbeit, Institut für Leichtbau Entwerfen und Konstruieren, Universität Stuttgart, 2004 [8] Yang H., Untersuchung zur Bestimmung der mechanischen Eigenschaften von Randverbundsystemen von Isolierglasscheiben, Diplomarbeit, Institut für Leichtbau Entwerfen und Konstruieren, Universität Stuttgart, 2006..

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Complex geometry glass balustrade: Eleftheria Square, design and construction.

Frederico Figueiredo, Pentagonal Lda, f.figueiredo@pentagonal.com Abstract The Glass structure of the West Balustrade in Eleftherias Square Nicosia-Cyprus presented a challenge to Pentagonal in terms of 3D modelling, special glass fittings fabric, glass production, installation and testing in order to achieve the goal of this long-waiting project. The design and construction of this prominent and futuristic design by Zaha Hadid Architecture project required input and expertise from Architects, Structural engineers, Software engineers, Glass specialist’s engineers and General contractor builder.

Project Overview A glass balustrade may be more than the functional propose, may be a land mark or point of cultural reunion creating an urban plaza for the city of Nicosia connecting both sides in the last divided capital of Europe. Today’s architectural demand for complex geometry has been developed to attain maximum transparency in more organic forms to improve the well-being of users and maximize interaction with the outside.

This glass balustrade was produced by Pentagonal and has an inclination of 42º along its length with non-regular curved geometry to create a glass balcony faced to west.

Structural glass elements and software modelling were specifically developed, simulated and tested to ensure that not only the structural but also the aesthetic performance of the glass structure is guaranteed.

The architecture design was made by Zaha Hadid studio modeled and manufactured by Pentagonal Fitechnic systems with Eckersley O’Callaghan and Hyperstatic structural engineering, general contractor was LOIS Builders from Cyprus.

Balustrade Design The scope of work for Pentagonal was to construct a glass balustrade with variable curved geometry composed by 20 metallic (mild steel

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painted) posts, fixed on an embedded plate (on concrete); with infill of 10+10mm glass laminated with interlayer Sentryglas posed in a stainless steel bottom shoe channel (stainless steel AISI 316) and fixed between posts by a superior patch fitting plates (stainless steel AISI 316) connected to the posts.

The balustrade is an inclined 42Âş glass panel cantilevered in a variable height from a bottom continuous channel and fixed on top aprox. 400mm from the edge with 2 stainless steel pates connected to a mild steel, to create a 1,10m height barrier.

The primary elements of glass balustrade are described below, and are as follows: 1. Mild steel embedded plate cast-in placed located on site before installation of balustrade 2. Mild steel metallic posts painted in color RAL 3. Welded stainless steel anchor plate with blocks for threaded holes bottom shoe (int) 4. Welded stainless steel L plate with countersunk bolts on the bottom shoe (ext) with whip holes to allow for drainage 5. Welded superior stainless steel plate (Ext) with blocks for threaded holes 6. Welded Stainless steel A1 hardware to Superior Ext Stainless steel plate 7. Welded stainless steel T arm connection 8. Connecting patch fitting A2 hardware 9. Welded superior stainless steel plate (int) with countersunk holes

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10. Curved and straight laminated fully toughened glass 10+10mm with SGG Bright silver coating and Sentryglas interlayer Detail Design Glass panels modeled with variable sizes and shapes aprox. 3,50m length and 1,70m height were supported by an off the shelf profile bottom shoe channel with the capability to withstand the wind and snow loads to a deflection limit set at L/120 and maximum 25mm for barrier loads. No deflection design criteria was considered for seismic and the panels were restrained with structural silicone.

The dead load of the panels was supported by 2 or 3 (for curved glass) nylon bearing blocks per panel located on the bottom connection and also blocks on the top connection. The glass was produced with notches concealed by the capture plates, to allow for structural connection.

For the end panels located in of the west balustrade, a 5,8m glass length was installed but partially not supported by the bottom shoe so the dead loaded was supported on the top capture in the end of the balustrade. Calculations using FE software MEPLA SJ models were made in order to confirm stresses on glass.

Modelling Process The 3D modelling of the geometry of the West balustrade was created using Rhinoceros (Rhino) software in order to create solids and polygon meshes.

The modelling is based on the 3D point cloud survey received from client and all parametric modelling was done by the Grasshopper graphical algorithm, plugin to the Rhino software. This allows to rearrange automatically any small change in the final survey from client.

The topographic measures (survey) were done by client in 2 stages: after implementing the embedded plates, and after the casting of the concrete for verification accordingly to the reference points. The output from this survey was a 3D point cloud in Rhino to be basis of the modelling work.

Complex geometric suggested to model in Grasshopper in order to help verify and make possible to apply any

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changes in the global geometry, orienting all modulation to a specific geometric guideline which is the reference to all process.

Grasshopper is an algorithm modelling software that interacts with Rhinoceros, allowing the inputs in the grasshopper automatically rearrange the global model created, adjusting for example: 1. Change the diameter in any hole 2. Change dimension in any plate 3. Change position of posts 4. Automatic adjustment in a specific line On Grasshopper interface was created specific individuals reference Set Points related to crucial locations of the balustrade like the post and “T” arm connection, XY position of post base plate and top edge of glass in order to edit individual values as well as “move” all in once, without compromising the smoothness of the free form curves of the balustrade.

The modelling was created using the guideline of the pre-cast survey, adjusting to the final in site free form curve and final 3D modulation was presented in Rhino file *.3dm, with solids elements implemented in the concrete Casting molds (in blue), delivery to client for approval.

Besides the guideline was also taken in account also the different axis of all posts for installation.

The various parts were exported from Rhino to CAD files and TEKLA STUCTURES in order to create the construction drawings and to follow the procedure for the rest of the scope of work.

Production of the components and testing The production of the balustrade elements was composed

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by glass elements, stainless steel parts (bottom shoe, top plates) and painted mild steel (posts).

The laminated glass was composed by one sheet of 10mm extraclear glass and 10mm coated reflective glass (SGG bright silver) with Sentryglas 1,54mm interlayer.

The glass edgework was produced by CNC done before hand (edge polishing, holes, notches, etc.), and followed by curving in a horizontal longitudinal bending with radius adjustment controlled by PLC. Immediately afterwards, the already curved geometry is quenched (fast cooling).

After tempering glasses were submitted to Heat Soak Test (HST) in order to prevent risk of tempered glass spontaneously breaking, due to inclusions.

The interior bottom shoe was composed by 316 stainless steel laser cut parts, 8mm and 12mm plates TIG welded in a 42º angle, having 40x40mm blocks spaced 50mm between them. The exterior bottom shoe composed by a 8mm 316 stainless steel “L” shaped with M10 countersunk bolts each 150mm. Posts were 35mm thickness SJ275R mid steel laser cut, welded in MIG continuous wire welding and painted scheme as follows: SA 2 ½ 7K-800 60µm primary, 7L-150 µm intermediate and finish in 50 µm 7P258 RAL 9010. Superior plates 316 stainless steel 20mm and 25mm thickness were TIG welded with blocks to fix the “T” from post with M10 and M16 countersunk bolts.

The “T” part connection between post and stainless steel superior plates steel were produced in Stainless Steel 2205 Duplex.

All balustrade metallic parts were curved and preassembled in factory with 3mm tolerance in all XYZ axis to fulfill specific project requirements, gap joint of 10mm between stainless steel plates and 20mm between glasses with center line of gap aligned with the post. All qual-

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ity inspection was carried out by a third part (Bureau Veritas).

A prototype of the balustrade was produced in factory for approval and tested based on EN950: a) soft impact test releasing a sandbag of 50Kg to a height of 1,50m without damage; b) hard-body impact test releasing a metal ball of 4,5Kg up to height of 1,50m without damage; c) Post-breakage stability recording deflections of 3mm when breaking first glass panel and 5mm after breaking second glass panel outstanding his self-weight and stability for more than 10 days.

Site Installation The assembly methodology on site had different phases, the order of operations being as follows: 1. Implementing the embedded steel plates 2. Assembly metallic posts 3. Assembly bottom shoe interior and exterior parts 4. Glass assembly 5. Assembly of superior stainless steel plates, interior and exterior parts 6. Sealing and finishing

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Posts were installed with 8xM24 chemical anchor and filled with RE-500 Hilti epoxy. The embedded steel plates were placed in-cast concrete accordingly to model and the bottom shoe installed with M8 rod and deviations of implantation of no more than 10 mm in all the threedimensional directions. The glass was installed through the “drawer”/ cavity space of the bottom shoe placed in Nylon bearing blocks attached to VHB tape and fixed around the notches on the top plates. The gap between bottom shoe and glass was filled with a 15x8mm structural silicone DC895. The superior plates gaps were filled with structural silicone DC895 and finished with weather seal 10mm silicone DC791.

Acknowledgments The work was done by Pentagonal with the involvement and acknowledgment of among others Zaha Hadid Studio, Eckersley O’Callaghan Engineers, Hyperstatic, Cricursa, Cruzdeoito, Seveme and LOIS Builders.

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An engineering approach for the basic design of glazed surfaces under blast waves Massimo Maffeis a| Gianni Royer-Carfagni a,b,c| Luca Viviani a,b (a)

Maffeis Engineering S.p.A., Via Mignano 26, I 36020 Solagna (Vi), Italy

(b)

Department of Engineering and Architecture, University of Parma, Parco Area delle Scienze 181/A, I 43124 Parma, Italy

Construction Technologies Institute – Italian National Research Council (ITC-CNR), Via Lombardia 49, I-20098 San Giuliano Milanese, Milano, Italy (c)

email: m.maffeis@maffeis.it, gianni.royer@unipr.it, luca.viviani@.unipr.it

Keywords: Glass façades • Blast-wave • Lumped element model Abstract Nowadays the design of blast-resistant glazed façades is acquiring importance to comply with building safety standards. The high-pressure generated by the blast-wave air-front can lead to catastrophic failure of the glass panes and/ or their load-bearing structure, with possible projection of fragments that constitutes a potential threat for human lives and properties. The timedependent deformations-history is usually assessed via numerical analyses and/or experimental investigations, but it is difficult to recognize the role of each element in the dynamic response of the whole. Here, to guide structural design, we propose a simple analytical model that permits a synthetic view of the phenomenon.

The dynamic interaction among the blast wave and the ensemble of glazed panels and load bearing structure is studied in few paradigmatic lumped element models, representing glass panels supported by beams or tensioned cables, using Rayleigh’s method to reduce the plate-behavior of each glass panels to a single degree-of-freedom oscillator.

With reasonable approximations of the Friedlander waveform, the dynamic equations are solved. This analytical treatment quantifies the importance of the load-bearing structure in absorbing the biggest part of blast wave energy, to preserve the integrity of glass.

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Introduction The use of large glazed surfaces presents critical aspects associated with the intrinsic brittleness of glass, especially when the building is potentially exposed to terroristic threat. In order to protect people and properties in critical buildings against acts of malicious behavior, safety standards have been approved for the design of security glazing able to resist the effects of accidental or intentional explosions. In 1990 the Departments of the Army, of the Navy and of the Air Force of the USA, licensed a tri-service manual [1] to define and assess the last resistance capacities of facilities, defining the effects of explosions. In Europe, the ISO 16933 [2] has provided since 2006 a procedure to determine the air-blast resistance of glazing, introducing blast models for vehicle and satchel bombs in order to classify glazing performance within a broad range of blast parameters. Harmonized methods to analyze and test the resistance of glazing and windows under blast-loading conditions, including experimental methods with high explosives or blast simulators (shock tubes), have been collected in the technical document EUR-26440 EN(2013) [3], edited by the European Joint Research Center (JRC).

The structural design of glass façades under violent blast loads is usually conducted through experimental tests, possibly corroborated by numerical analyses, but only a few results can be found in the literature, since they are mostly assembled in confidential documents. Recently published studies are focused on the determination of the blast capacity of isolated laminated-glass panels. In general, soft polyvinyl-butyral (PVB) interlayers with low adhesion properties achieve the best safety performance with no interlayer tearing, while still efficiently retaining glass

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fragments [4]. Various numerical models can be used to simulate the failure of the glass as well as of the interlayer [5]. However, to our knowledge, a limited attention seems to have been paid at the assessment of the capacity of the entire glazed surface (façade), for which the dynamic interaction of the glass panels with the rear load-bearing structure has to be taken into account.

In general, the state of stress in the glass panels may be consistently reduced if the supports are properly designed so to adsorb most of the energy from the blast wave.

Numerical models were used in [6] to demonstrate that special elastic-plastic connectors, interposed at the interface between a building structure and the glazing façade, can effectively contribute to safeguarding the integrity of glass. Here, we focus the attention on the rear load-bearing structure, with the aim of optimizing its mechanical properties with respect to its dynamic interaction with the supported glazed panels. Therefore, we propose an analytical model based upon a schematization with lumped elements, which can provide, with a reduced number of parameters, a synthetic view of the complex dynamic response under a blast wave. A parametric analysis of paradigmatic case studies furnishes a guide for a design in which the rear supporting structure absorbs most of the energy released by the explosion, thus reducing the stress in glass. To this aim, the stiffness and inertia of the rear structure shall be optimized as a function of the mechanical properties of the supported glass panels, while fulfilling the constraints related with the serviceability limit states of the façade under design actions.

The lumped element model The considered case study is represented in Fig. 1a: a façade is composed of three horizontal rows of rectangular glass panels connected to vertical supporting elements, which can be either cables or beams. Supposing the façade is very wide, one can use symmetry to study the response of one glazed column formed by three glass panels supported by one vertical element, as indicated in Fig. 1b. Here the panels are supposed to be contoured by a secondary frame, assumed to be rigid, which in turns is connected to the vertical rear supporting structure.

Although the panels are fixed to the rear structure at the corner points, we schematically consider a fictitious one-point connection in correspondence of the centroid of each panel, further supposing that also the mass of the vertical rear structure is lumped at such fixation points.

In the following, we will reduce the vibration of each glass panel, supposed to be simply supported at the borders by the secondary rigid frame, to that of a simple 1-DoF (Degrees of Freedom) oscillator. To do so, we will use Rayleigh’s method via the definition of a proper shape function for the plate deformation, which will depend only upon the displacement of one representative

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Figure 1 a) Case study of a façade composed of three horizontal rows of glass panels. b) Simplified 6-DoF model. point, i.e., the panel center. Therefore, as summarized in Fig. 1b, the configuration of the vibrating system can be defined by six scalar functions of time: the three horizontal displacements Zi(t), i = 1...3, of the points of the rear structure where the mass is lumped and to which the glasses are fictitiously connected, together with the three displacements Zi(t), i = 4...6, of the centers of the glass panels that completely define, through the assumed shape function, the out-of-plane displacement of any point of the panels themselves. In conclusion, one has to handle a 6-DoF system.

All the glass panels are subjected to an out-of plane force per unit area p(t) [Pa] consequent to a travelling blast wave, which is considered uniformly distributed on the panel surface. The form of p(t) is interpreted according to the Friedlander’s relation, which reads

where, for the case at hand, we assume A = 0.82, Pmax = 50 kPa, and T1 = 0.025s. This equation prescribes that compressions (negative force per unit area) are followed by suction pressure (positive force per unit area) at t = T1 . The panels of the façade are identical one another, monolithic of size a x b x c = 2 x 2 x 0.02 m3 and with the mechanical properties of float glass (Young’s modulus GPa, Poisson’s ratio = 0.22, density = 2500 kg/m3). The case of laminated glass panels can be handled in an identical way by considering their effective thickness [7], i.e., the thickness of a monolith with equivalent bending properties.

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD The equilibrium equations of the system shown in Fig. 1a are obtained via Rayleigh’s method and Hamilton’s principle [8]. With reference to the notation of Fig. 1a, for the ith glass panel, i = 1...3 , consider a reference system (xi , yi) , with origin at one of the corners and axes parallel to the borders, so that the reference domain for the panel is { 0 ≤ xi ≤ a , 0 ≤ yi ≤ b }. The displacement field is defined by a shape function of the form

where ψ(xi ,yi) = sin(πxila)sin(πyilb). This is in agreement with the assumption that each glass panel is simply supported on its sides to the rigid frame, but the whole frame follows the displacement of the point where it is connected to the vertical rear structure. Different constrains could be assumed for the glass panels, and in this case the shape function ψ(xi ,yi) shall be modified accordingly.

The equations of dynamic equilibrium take the simple form

where Z(t) is a vector collecting the nodal displacements with and is the mass matrix, K the stiffness matrix and C the damping matrix. Proportional damping à la Rayleigh is assumed, with damping ratio for each one of the six vibration modes. The vector collecting the effective forces F(t) is calculated from the applied force per unit area p(t) of (1), by using the shape function (2).

All the quantities appearing in (3) are calculated using classical arguments [8] in the dynamics of structures. The system can be diagonalized according to the vibration modes and numerically solved using Duhamel integral [8].

The stiffness matrix establishes the correlation between displacements and forces in stationary conditions and, in particular, it strongly depends upon the mechanical/geometric properties of the rear supporting structure. In the following we will consider two different in type structural elements, i.e., cables or beams, whose length is assumed to be L = 9.6m, as a reference case.

Parametric analyses and results Despite its simplicity, the 6-DoF system of Fig. 1a allows for a synthetic parametric analysis of the dynamic response of the glazed façade, with particular attention at the role played by the rear load-bearing structure. Under the pseudo-impulsive load (1), the whole façade starts oscillating and, depending upon the stiffness and type of the rear structure (cable vs. beam), there is a different dynamic interaction with the vibration of the panel, as qualitatively represented in Fig. 2. The fact that the assumed Friedlander waveform prescribes both positive and negative (suction) pressures complicates the interaction.

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Figure 2. Dynamic interaction between the vibration of the panels and the rear load-bearing structure in the simplified 6-DoF system. Snapshots of the representative deformation at three different times.

Of course, the Achilles’ heel of the whole vibrating system is represented by the glass panel, whose integrity should be preserved as much as possible. Within the approximations of Rayleigh’s method, the state of stress in the i – th panel, i = 1..3, can be obtained from double differentiation with respect to the spatial variables (xi, yi) of the assumed shape function of (2) for the panel deflection. Therefore, within the hypotheses of the model, the state of stress in the glass at time t is directly proportional to the quantity . This quantity should be compared with the value δ that corresponds to the displacement of the centroid of the panel when the maximum pressure pmax of (1) statically acts on it. Indeed is related with the state of stress under static conditions. In conclusion, the quantity is the ratio between the maximum stress in glass for the vibrating façade and the corresponding value if the glass panel was statically subjected to the maximum pressure from the blast wave. Hence, it represents a measure of the potential gain, in terms of stress state in glass, obtainable by properly designing the rear structure.

Cable supported façade When the rear structure is formed by a vertical cable, its stiffness depends upon the tensile force T to which it is subjected. We will suppose that the value of T does not vary during the motion, although large displacements could certainly modify it. We will further assume that the cable has a mass per unit length mc [kg/m], which does not necessarily correspond to the weight of the cable itself since, in addition to the glass panels, there may be other masses (fixing devices, secondary frames) directly supported by the cable. Moreover, the cable could be artfully ballasted in order to improve the dynamical response of the façade, if required.

The maximum deflection of the cable under the blast wave (1) is represented by the maximum absolute value of

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD X2(t) achieved during the motion (Fig. 1b). This quantity, synthetically indicated as [mm], is represented in Fig. 3 as a function of mc [kg/m] and T [KN]. As expected, Z2,max diminishes by increasing T , because the cable is stiffer, and by augmenting mc , since the inertia forces contribute to equilibrate the applied blast wave, especially when the sign of the pressure is reversed, as per Friedlander’s equation (1), passing from compression to suction. In general, the standards [1] [2] [3] do no prescribe a serviceability limit state for the cable deflection under blast waves, but a reasonable limit may be assumed of the order of L/10 , which for the case at hand ( L = 9.6 m) is about 1000 mm. All the points of the graph plotted in Fig. 3 satisfy this limit.

The absolute value of the maximum stress [MPa] acting on the central panel i = 2 , calculated through the shape function for deflection of (2), is reported in Fig. 4, again as a function of [kg/m] and [KN]. Recall that, within the approximation of the model, results to be proportional to the maximum absolute value of . This graph presents heights and valleys and it is qualitatively different from that of Fig. 3.

Observe that, in general, the stress tends to increase by augmenting the mass and the tensile force in the cable.

This is because the stiffer the cable is, the more the glass panel is affected by the power of the explosion. When the rear load-bearing structure is very deformable, the blast wave provokes the sudden displacement of the whole panel, so that the corresponding inertial forces can equilibrate the applied pressures without appreciable deflections of the plate. However, the fact that the compression pressure is followed by a suction pressure complicates the dynamic interaction.

To our knowledge, there is not unanimous agreement about what is the strength of glass under high strain rates. Whereas the influence of strain rate on the compressive strength is not observable, the influence on the tensile strength seems to be appreciable. Since a threshold of 200 MPa has been previously assumed for annealed glass [4], considering that the benefic effect of thermally-induced prestress should not be affected by the strain rate, we may tentatively indicate that the maximum tensile stress in a thermally toughened glass should be of the order of 85 MPa. The intersection of a horizontal plane corresponding to such a value with the graph of is evidenced with a red curve in Fig. 4.

Under the static action of the elastic deflection of the glass panel is mm, which corresponds to a maximum tensile stress MPa far beyond the strength of glass. The maximum absolute value of the relative displacement attained during the motion, referred to as normalized by the static deflection , is represented in Fig. 5. For what stated above, represents the ratio between maximum stress in glass either in the vibrating

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Figure 3. Cable supported façade. Maximum absolute displacement Z2,max [mm] as a function of the tensile force T [KN] in the rear cable and its mass per unit length mc [kg/m].

Figure 4. Cable supported façade. Maximum stress σ [MPa] in the glass central panel as a function of the max tensile force T [KN] in the rear cable and its mass per unit length mc [kg/m].

Figure 5. Cable supported façade. Maximum absolute value of the relative displacement Z5 – Z2 normalized by the static deflection δ, as a function of the tensile force T [KN] in the rear cable and its mass per unit length mc [kg/m].

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Figure 6. Beam supported façade. Maximum absolute displacement [mm] as a function of the moment of inertia [cm4] in the rear supporting beam and its mass per unit length [kg/m].

Figure 7. Beam supported façade. Maximum stress [MPa] in the glass central panel as a function of the moment of inertia [cm4] in the rear supporting beam and its mass per unit length [kg/m].

Figure 7. Beam supported façade. Maximum absolute value of the relative displacement normalized by the static deflection , as a function of the moment of inertia [cm4] in the rear supporting beam and its mass per unit length [kg/m].

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façade or under maximum static pressure. Obviously, the minimum value is achieved when the rear supporting structure is the most compliant, i.e., when and are minimal. However, there are technological and structural limits. We have already specified that, under the imposed blast-pressure, one should have MPa but, under service loads, the deflection of the cable should remain within reasonable limits. Imposing that under a wind pressure of 1 kPa the maximum deflection of the cable is not higher than L/50 , one finds the lower bound In Fig. 5 the region of the graph that respects the aforementioned limits is etched with dots. Within this region, the point corresponding to the optimal value is evidenced with a red ball, with coordinates . The corresponding maximum stress in glass is . Assuming that the design strength for the steel forming the cable is , a minimal area Ac,min 300mm2 is required, which corresponds to a mass per unit length mc,min 2.34mm2 kg/m. Since mc,min < 6.25 kg/m, one deduces that the cable should be ballasted in order to reach the optimal value of the mass. However, the graph of Fig. 5 indicates that the dependence upon the mass is much less than upon the tensile force in the cable. Consequently, the advantage that could be obtained by ballasting the cable is not relevant.

Beam supported façade Suppose now that the same glazing of Fig. 1a is supported by vertical steel mullions. The system is the same schematically represented in Fig. 1b, where the cable is now replaced by a steel beam of the same length . Let GPa denote the Young’s modulus of steel and I the moment of inertia of the beam, so that its bending stiffness is proportional to The beam has a mass per unit length which may include a ballast. The maximum deflection under the blast wave (1) is represented by the maximum absolute value of , again synthetically indicated as [mm], which is plotted in Fig. 6 as a function of [kg/m] and the moment of inertia I [cm4]. Observe that, similarly to Fig. 3, diminishes by increasing I , but the dependence upon the mass is even milder than for the case of a cable supported façade. In fact, the stiffness of the beam is overwhelming with respect to the inertial forces. Following practical rules, we assume that in the serviceability limit state under blast waves, the beam deflection should be less than L/25 = 384mm mm. This is a much stricter limitation with respect to the previous case, dictated by the “physiological” reduced deformability of a beam with respect to a cable.

In fact, to increase the compliance, the cross-sectional moment of inertia should be very small, but this is in general not compatible with the elastic section modulus that the beam should have in order to maintain the stress below the

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD yielding limit. The intersection of the graph of with the horizontal plane at the quote L/25 is marked with a red curve in Fig. 6.

The maximum stress [MPa] in the central panel , again calculated by using the shape function of (2), is represented in Fig. 7 for varying I [cm4] and mb [kg/m]. Observe that, also in this case, the dependence upon the stiffness is much more marked than the inertial contribution. In general, the stress is very high, of the order of 500 MPa for realistic values of the beam bending stiffness. In order to reduce the stress, one should reach the “cliff” in the surface plot, associated with values of I less than 1000 cm4. Setting a limit stress of 200 MPa, as in the previous case, one obtains the red curve marked on the graph of Fig. 7, which corresponds to a moment of inertia i of the order of 500 cm4. This is indeed a very low value for the bending stiffness, which would provide a very high deflection , of the order of 800 mm, as indicated from the comparison with the graph of Fig. 6. The conclusion is that, in order to limit the state of stress in the glass panel, the beam should have a compliance comparable with that of a cable, but this is in general not compatible with the condition that the stress in the beam remains within the design limit.

The plot of the maximum absolute value of attained during the motion, normalized by the static deflection of the glass panel under the maximum pressure , is represented in Fig. 8. The region corresponding to the serviceability limit state is etched with dots and, within this region, the optimal point is the one marked with a red ball, corresponding to However, the corresponding maximum stress in glass is , a value that is far beyond the admissible limit for glass strength, even at very high strain rates.

From the comparison with the results obtained for the cable, one can infer that, for the case at hand, the use of a beam as a rear supporting structure is not recommended. In fact, in general a beam is too stiff to provide noteworthy benefits in terms of stress in the glass panels.

Conclusions A lumped-mass model has been proposed to describe, in simple terms, the dynamic response of glazed-façades to impulsive loads like those consequent to an explosion, here modelled according to Friedlander’s equation.

A parametric analysis has been made by considering a rear load-bearing structure, supporting the glass panels, with variable stiffness and mass. The case-studies of cable- and beam-supported façades have been examined.

Despite its simplicity, the proposed schematic model well indicates the role played by the rear load-bearing struc-

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ture during an explosion that occurs in proximity of the glass façade. The analysis suggests that the rear structure should be designed in such a way that it can adsorb, within its kinetic and elastic strain energy, a relevant part of the energy from the blast wave, so to reduce the stress in the supported glass panels and preserve their integrity. In general, a cable structure performs much better than a beam structure, because the former is much more compliant than the latter. The cables should be ballasted in order to achieve the optimal value of the mass per unit length that minimizes the stress in the glass panels, because this mass opposes to the suction pressure following the compression pressure from the blast wave.

We believe that simple models, like the one presented here, can be of help in the preliminary design of a blastresistant façade, because they can provide a concise but complete view of the complex dynamic/structural response. In particular, simple models should be used to decide the optimal geometric and material properties of the rear structure to safeguard the glass integrity. The present study suggests that, with an accurate design of the rear structure, the maximum stress in the glass can be strongly reduced with respect to the stress that would develop if the panel was invested by the blast wave while rigidly supported.

References [1] TM S-1300/Navfac P-397/AFR SS-22, Structures to resist the effects of accidental explosions, The Departments of The Army, the Navy and the Air Force of the USA , 1990.

[2] ISO 16933:2007, Glass in building - Explosion-resistant security glazing -Test and classification for arena air-blast loading, International Organization for Standardization (ISO), 2007.

[3] S. Alexander, A. Van Doormaal, C. Haberacker, G. Hüsken, M. Larcher, A. Saarenheimo, G. Solomos, L. Thamie and G. Valsamos, EUR 26449 - JRC87202. Resistance of structures to explosion effects, Office of the European Union, 2013.

[4] J. Pelfrene, J. Kuntsche, S. V. Dam, W. V. Paepegem and J. Schneider, “Critical assessment of the post-breakage performance of blast loaded,” International Journal of Impact Engineering, 2015.

[5] M. Lancher, G. Solomos, F. Casadei and N. Gebbeken, “Experimental and numerical investigations of laminated glass subjected to blast loading,” International Journal of Impact Engineering, vol. 39, pp. 42-50, 2012.

[6] C. Bedon and C. Amadio, “Glass facades under seismic events and explosions: a novel distributed-TMD design concept for building protection,” Glass Structures & Engineering, vol. 3, pp. 257-274, 2018.

[7] L. Galuppi and G. Royer-Carfagni, “Effective thickness of laminated glass beams: New expression via a variational approach,” Engineering Structures, vol. 38, pp. 53-67, 2012.

[8] R. W. Clough and J. Penzien, Dynamics fo Structures, Computers & Structures, Inc., 1995.

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Development of a CCF Glass Tube Façade in Hong Kong Martien Teich, Christian Rehner, Fabian Schmid seele GmbH, Gutenbergstraße 19, 86368 Gersthofen Keywords: Glass tube façade, Closed Cavity Façade, CCF, Hong Kong Abstract This paper deals with the development and construction of a novel 2,308 sqm glass tube façade engineered by Eckersley O’Callaghan (EOC) as façade consultant and turned into reality by seele. The glass tube façade consists of 307 tubes made of laminated safety glass, 238 half- and 69 full-tubes with a height of 9m and a diameter of 900mm. Aluminium profiles connect adjacent tubes with each other.

Each tube has a cut duplex-stainless steel lid at top and bottom fixed with structural silicone. The façade is located in Hong Kong’s humid environment with very high hurricane wind loads. An adopted closed cavity façade (CCF) system pressurizes the tube due to the large enclosed air volume in the cavity. seele conducted extensive testing both in Germany and Hong Kong to confirm the feasibility of the system.

Half glass tubes were bent and laminated in Europe, shipped to Hong Kong and structurally bonded to form full glass tubes before installed in the high-rise building in Hong Kong.

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Introduction The closed cavity technology is a well-known and established approach for multi-layered façade systems in order to pressure-equalize the façade cavity and prevent any condensation on the glass surfaces. The closed cavity façade system increases the acoustic performance, integrates shading devices, minimizes cleaning effort, increases floor space in comparison with naturally ventilated double façade systems, and provides maximum comfort for the building tenants.

This paper shows that the CCF technology also has some great advantages for non-traditional applications.

This paper first outlines general design principles for closed cavity facades. The authors discuss key aspects for special geometries and the climatic area of Hong Kong in comparison to Europe. Finally, it is shown how the volume flow of dried air through the tube influences the risk of condensation.

General Design Principles for CCF Closed cavity façades use a pressurized air supply or a ventilation system known from the concept of pressurized multilayer ETFE-foil cushion constructions. Dried, filtered and sometimes tempered air is blown into the system to manage condensation for the cushion constructions.

Mechanically driven vents or compressors, stainless steel pipework and valves are used as an air supply system. Filtration and exclusion of any contaminations of the supply air is essential in order to ensure a performing cavity condition. The designers can adjust the system performance to a more tolerant or a more effective configuration.

Tightness of the elements and the pipework, an adjusted flow rate typically in the range of 3 to 40 l/h∙m3 can fulfill most project specific demands.

The CCF concept typically simplifies the glazing element in order to provide shading, light control and regulation functions as well as climate load management in one system. Realized projects are mostly high-rise buildings with office use. However, the CCF concept is also suitable for safe operation of double skin façades in challenging climatic conditions. With an appropriate design, the

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Figure 1. 9m high glass tubes for the New World Centre in Hong Kong. © seele

technology offers performance reserves and can safely control even extreme weather situations and critical climatic influences. Even extreme geometries of the glazed elements can be realized as shown in subsequent paragraphs.

The CCF design needs to configure a system with an appropriate airflow rate in order to avoid condensation under almost every environmental condition, to handle climatic and other pressure induced loads, and to minimize energy consumption. The challenge of the development is the understanding of the influences of heating and cooling on the special geometry and in the development of a defined flow rate in order to avoid congestion as well as heating. In order to define the flow rates and the optimal inflow and outflow openings, different full-size mock-ups and numerical calculations are used. The CCF elements are generally manufactured in clean rooms. The elements are conditioned over the entire processing and supply chain until installation and commissioning in order to prevent unwanted substances entering the cavity.

air. Filtration and exclusion of any contaminations of the supply air is essential in order to ensure a performing cavity condition.

New World Center Hong Kong The unique glass tube façade shown in Figures 1 and 2 is an attractive addition to the New World Centre in Hong Kong, a hotel and office complex in Kowloon. seele built the main façade of the New World Centre with 307 glass tubes and a special LED lighting technology between the tubes. A part of the façade is equipped with CCF technology, which is subject to special physical requirements.

The whole building needs to withstand high wind loads and building movements. The CCF-system is integrated in 69 full and half tubes. Two individual CCF supply systems control the east and west façade elements separately to consider the different climatic boundary conditions.

At the lower end of each tube, a small vent is integrated ensuring a pressure compensation. The mechanically driven ventilation, stainless steel pipework and valves are used for the air supply with dried, filtered and tempered

Hong Kong Climate Analysis Knowledge and understanding of the local climatic conditions play a key role in the correct sizing of the technical equipment and the adjustment of the system when using facades and in particular CCF facades. In preparation for the project shown in Hong Kong, seele carried out basic system investigations both in Gersthofen (Germany) and Hong Kong in order to define the system parameters for a safe and long operation.

An important survey at the beginning of each project is the evaluation of local climate data in order to give a detailed assessment for the design process. Hence, the following sections describe the most important climatic differences between Gersthofen (Germany) and Hong Kong as well as their influences on the system design.

Gersthofen in southern Germany is mainly influenced by the moderate warm climate in the Alpine foothills. The

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Figure 2. Polished duplex-stainless steel lids for the glass tubes. © seele

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD climate classification according to Köppen and Geiger characterizes it as a warm temperate, always humid climate with warm summers. In comparison, Hong Kong is influenced by the temperate, warm coastal climate. In summer, Hong Kong receives significantly more rainfall than in winter. According to the Köppen-Geiger classification, Hong Kong has a warm temperate, dry winter climate with warm summers. Those climatic characteristics can also be seen in the analysis of representative weather data. The outdoor temperatures in Hong Kong are significantly higher than in Southern Germany. The average annual temperature in Gersthofen is 8.5°C and in Hong Kong 22.5°C. In addition, the absolute humidity and the vapor pressures are significantly higher in Hong Kong than in southern Germany.

If the climatic conditions in the cavity adjust too slowly, rapid temperature drops or rapid vapour increases of the outside air can lead to condensation on the inside of the glass tubes as well as on the frames. For a good assessment of the functionality of CCF facades, two parameters are relevant and can be determined from representative weather data: The extent of temperature and humidity changes (rise and drop) and their probability distribution.

Figure 3 shows a comparison of the probability distribution of temperature rises and drops as well as changes in vapour pressures for Gersthofen and Hong Kong. Cor-

ridors from 0 to 0.75 Kelvin per hour, 0.75 to 1.75 K/h and 1.75 to 3 K/h are identified to differentiate between noncritical, critical and very critical changes. In the investigation of the humidity change, the partial pressure of water vapour is categorized with pressure change rates of 0 to 125 Pa, 125 to 250 Pa and 250 to 375 Pa. The partial pressure is another measure for the humidity change in the air, as it provides an absolute value that is independent of the prevailing temperature and gives an indication of the direction and the amount of vapour movement. Due to a partial pressure change rate, the quantity of the actual moisture input and output is evaluable independently from temperature influences.

Critical temperature increases and decreases occur more frequently in southern Germany than in Hong Kong.

In addition, the comparison highlights that larger temperature drops and rises in the range of 0.75 - 3.75 K/h occur in southern Germany. Hong Kong is less critical due to the lower and less frequent temperature changes.

The comparison of the partial vapour pressures and their changes show that more humid air is present in Hong Kong (as expected) and that critical drops and rises in the range of 125 - 375 Pa/h are significantly more frequent than in Germany.

The comparison leads to the conclusion that Gersthofen is more critical to temperature fluctuations and

Figure 3. Probability distribution of temperature changes and partial vapour pressure in both Gersthofen (Germany) and Hong Kong. © seele

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD may condensate more frequently from rapidly changing weather conditions. Hong Kong is more critical due to the much greater amount of moisture in the air which, when coupled to the cavity interior, represents a condensation risk at much lower temperature changes. This leads to the recommendation that CCF facades in Hong Kong should be operated with preconditioned extract air from the air-conditioning system. This has the advantage of significantly lower amounts of moisture, which must be buffered otherwise by machine technology of the CCF air-processing unit.

System Testing In order to define the flow rates and the optimal inflow and outflow openings, seele built different full-size mockups as shown in Figure 4 to investigate different system parameters by means of long-term measurements. The test engineers constantly control the system during operation to monitor conditions and detect critical changes at an early stage.

The geometry and the volume of the CCF-facade influence the design of the ventilation systems. In Hong Kong,

Figure 4. Visual and performance mock-up. © seele

seele built two geometric types: full tubes and half tubes.

The full tubes have a diameter of 900 mm, a height of 9 m and an internal volume of 5.1 m³. Due to their geometry, the half tubes have 50% of the volume of the full tubes.

In various test series, seele measured surface temperatures on the inside of both the full tubes and the half tubes.

Figure 5 shows representative temperature measurements for a two-day period. The half tube shows higher absolute temperatures and faster temperature rises than the full tube. This is due to the smaller air volume and the reflective coating of the rear pane of the half tube.

Half tubes tend to have lower dew points and react more quickly to system conditions.

In a second step, the engineers compared the measured temperatures with the dew point temperature of the climate prevailing in the tube. Depending on the volume flow, which was set to condition the tubes with dried air at low pressures, higher or lower temperature differences were recorded between the surface temperature on the glass pane and the prevailing dew point temperature.

Figure 6 illustrates some selected results: The higher the volume flow, the lower the risk of condensation. Due to the smaller volume of the half tubes, they are better conditioned at the same air flow rate than the full tubes.

This has a positive influence on the dew point of the half tubes. The difference between half and full tube is quite pronounced at the lower air flow rates of 20 l/h and 150 l/h. In the case of the full tubes, there are increasingly lower temperature differences and thus a greater possibility of condensation in comparison to the half tubes.

The full tubes are a more sluggish system and should be conditioned with a higher volume flow.

The results were combined with a risk analysis for detailed planning and a suitable air flow rate in order to take into account the economic effects of building operation. The pipe diameter of the ventilation system is

Figure 5. Temperature comparison between full and half tubes (surface temperature). © seele

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD selected according to the design of the defined air flows in order to avoid unnecessary pressure losses. The choice of the ventilation unit depends on the pressure losses in the pipe system and the required air flow rates. Hence, an optimal air flow rate reduces the energy consumption during the lifetime of the CCF system.

Summary This paper discusses several aspects for the design and engineering of closed cavity façade systems. As shown, the CCF technology can also be the technology of choice for modified and non-classical façade elements as the tube façade for Hong Kong’s New World Center. The authors compare the climatic conditions in Central Europe

(Germany) and Hong Kong. Although the air in Central Europe has generally lower medium temperatures and a lower humidity, the cavity temperatures in the CCF tubes change more quickly than in Hong Kong. In Hong Kong, though, the engineers have to consider the high humidity of the outside air when designing the CCF system.

CCF systems offer a good solution to avoid condensation in multi layered façade systems. Nevertheless, the optimization of the air flow rate, the reduction of energy consumption and operation costs need to be taken into account. Therefore, the system components and the integrated sensors can be used for a future optimization of the system conditions within a holistic integrated system optimization for buildings.

Figure 6. Comparison of probability distribution of temperature differences between cavity temperature and dew point for half (brown) and full (blue) tubes for different air flow rates of 720 l/h, 150 l/h and 20 l/h. © seele

72 | Intelligent Glass Solutions | Summer 2019

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD

High Tec Achievable for Everyone Miguel A. Nuñez Diaz | ENAR. Architectural Envelopes Sergio Cobos Álvarez | Periferia SL, University of Castilla La Mancha Jesús M. Cerezo Miguel | ENAR. Architectural Envelopes Aurelio Dorronsoro Díaz | Periferia SL Keywords Refurbishment • Structural Glass • Skylight Abstract The aim of this paper is to show that it is possible to reduce costs while maintaining clear architectural, constructive and structural concepts. In the world of glass -especially within the structural glass useit is normal to see big projects, with huge budgets and big specialist companies involved, as the glass cube. However, thanks to this kind of projects, the technology is moving forward, and little projects with clear concepts can be developed. The main issue in all these projects is to maintain the main concept at every level: architecture, structural and constructive.

Once these concepts are clearly defined, and without other elements, it is easy to obtain great results with low economical effort. The Arturo Soria lobby is one of these projects, holding a clear architectural and structural scheme without other interactions. The project is the extension of an existing lobby, to grant new access requirements, stepping into the existing courtyard and creating a bigger space with more light and transparency, in a direct relation to the landscape. For this reason, all the enclosure has been made of glass, avoiding structural massive elements

74 | Intelligent Glass Solutions | Summer 2019

that do not allow this transparency. The enclosure is composed of a vertical façade with a free design, and a horizontal skylight, all in glass. To avoid massive structural elements, the horizontal glass skylights are supported by the vertical glass façade.

The skylight is supported by horizontal fins, fixed on one end to the building and on the other side to a steel beam spanning through the whole dimension of the courtyard. This beam is connected in its lateral edges to the building slabs, but in order to minimize its dimension, a new support is placed in the middle, over the vertical glass façade pane. To avoid the buckling of this element, two vertical glass panes are situated on both sides, perpendicularly, and fixed with structural silicone. In order to guarantee the load transmission in the correct way, some special steel fittings are installed within the enclosure. The structural and architectural concept is clear, and all the requirements are conditioned by these concepts.

A small local construction company was able to tackle the challenge of the construction, avoiding the use of façade or glass specialist sub-contractors, reducing to the limit the final construction cost.

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD Introduction This intervention in an office building aims to blur the limits between interior and exterior space, with a glass pavilion designed with curved geometries that merge with the garden creating a new fluid and hybrid landscape. The access is transformed into a new experience interior and exterior melt together.

The proposal was the winning entry in a restricted competition with a design & build format -which is not very common in Spain- therefore implying concept and construction (integrating architects, engineers and general contractor). The owners wanted to increase the value of the property, built in the beginning of the 90’s in the north of Madrid. The main challenge in the brief was to update the obsolete access space, meeting all the new access requirements and solving the existing functional problems.

But the real challenge in the project was to actually build a strong concept working with three very restrictive premises: •

•

•

Figure 1. Interior image of the Building

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The office building must keep its normal functioning during the works, which makes the planning a key issue.

It is necessary to integrate and coordinate other renovation works in the building such as the landscaping, the elevators renovation and other actions in the different halls in every floor. That requires an understanding of all the works as a total intervention.

Last, but not least, the most restrictive premise was the total budget of the project. All the works, including the project and the construction, must be ca. 620 €/m2.

Since the Modern Movement, the development of new technological solutions has given architects a huge freedom to design, with virtually no restrictions, but the challenge is still the same as it was in the primitive

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD

Figure 2. Main view of the intervention

cabin of abate Laugier –to manage the relation between man and nature, to obtain protection from the exterior and control the environment conditions. Many projects, in absence of any restrictions, use big budgets and every available piece of technology. This project, on the contrary, shows that strong and complex concepts and advanced technical solutions can also be undertaken within tight budgets, using conventional production systems.

Architectural Concept The existing building had several access problems. The

Figure 3. Exterior Image of the building

76 | Intelligent Glass Solutions | Summer 2019

main entrance was barely used and was not accessible for PRM. Most people used a little service entrance in the opposite façade of the building, on the other side of the elevators’ hall. The public desk was near the main entrance and had a difficult sight on this secondary entrance. Moreover, the new requirements for access control implied the installation of turnstiles.

Taking advantage of a remnant plot ratio allowance, the only possible strategy was to blur the limits of the access floor stepping into the patio, solving all the functional problems in one gesture. The proposal materializes into

Figure 4. Public Desk

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD a glass pavilion with curved geometries that blends with the garden in a new hybrid space. Curves favor a dynamic and continuous perception of the space and define gentle and organized spaces.

In this way, the design avoids any horizontal and vertical opaque elements. This together with the mentioned curved geometries and the transparency and reflections of glass help blurring the boundaries between inner and outer space.

The patio, that was almost hidden in the previous scheme, is revealed as the most attractive element in the building. Integrated with the geometries of an ongoing landscaping project, the 4,5 m high glass Pavilion allows the connection of the two entrances, centralizing the movements and integrating the patio in the building. A new frontal main access to the elevators hall allows to distribute the required turnstiles on both sides of the new public desk, located in the center. The new lightning in the patio, rising to the roof, gives more verticality and unifies the pavilion with the rest of the levels playing with crossed views, lights and reflections.

The aim of the proposal is to refurbish the space, but it is not simply a renovation of all the materials. As a matter of fact, maintaining some existing materials, like the granite floor, allows to accomplish the budget objectives. Instead of the standard tabula rasa approach, the proposal sheds a new light into the existing elements integrating the new and the old (for instance backlighting the green glass below the new perforated panels).

Structural concept The structural sketch is very clear. The main structural element is a new steel beam situated between the vertical façade and the horizontal elevated skylight. This beam and the other elements are supported on the existing structure, mainly over the slab of the first floor. The skylight is supported in the perimeter by the existing structure and the new beam. The vertical façade is supported on the lower slab, but it is stabilized on the top with the new beam for the horizontal loads.

The skylight is composed by transversal beams in the slope’s direction, supported exclusively on both ends: on one side over the actual structure and on the other side over the new structural beam. The position of the skylight does not coincide with the height of the structural slab, because the skylight must meet the horizontal transom of the existing windows, which is one meter above the slab. For this reason, it is necessary to include vertical corbels to adapt the difference between heights. These brackets, made of lacquered steel, are fixed over the front of the slab with a three-dimensional regulation in order to obtain the horizontal line on the top. These vertical elements are in the same position as the mullion of the existing building, to integrate them in the design. The fixing between the beams and the brackets is made with only

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Figure 5. Structural Sketch

Figure 6. Loads Scheme one screw that allows rotations but fixes the movements.

On the other side, the beams are supported on the new beam with the same system, but in this case a horizontal hole is situated in the beam in order to guarantee the longitudinal movements of the beam due to thermal expansion.

The new beam is supported on both ends over the existing structure. Just as the skyligth beams, the new frontal beam is 1,5m higher than the structural slab and it is necessary to include some brackets to reach the new level.

In this case, the position of the new beam is in the middle of two mullions, and therefore it is necessary to include a horizontal beam between these two vertical elements to connect the new beam, acting as a little bridge. In this horizontal brace, a steel perpendicular element receives the end of the new main beam. In one of the edges the joint is free to let thermal movements.

To avoid an important impact on the existing glass facade of the first floor, it is necessary to reduce the height of the new beam. This beam does not have problems with the horizontal dimensions, and therefore its depth is enough to support the horizontal loads without any other

Summer 2019 | Intelligent Glass Solutions | 77

GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD Constructive concept All the elements of this façade are made with glass, lacquered Steel and stainless Steel.

The vertical façade cladding is composed of single glasses from the bottom to the top. Some glasses are curved and others straight, all of them laminated composed of two panes of 12 mm and 2 layers of PVB, except for the central structural glass. These glasses are supported in the bottom and stabilized on the top. The support is composed of a Steel component that allows the vertical adjustment of the glass to guarantee its position.

This element is made by two vertical steel tubes, and one horizontal plate that can move between the steel tube.

To fix the horizontal movements a steel plate with the shape of the enclosure is situated in the exterior and the interior side. This plate is screwed to the vertical steel tubes. In the exterior part this plate has another L profile to guarantee the watertighness with the external joint.

Figure 7. Support in the middle glass

support. But its vertical dimension couldn’t be more than 170 mm. With this height, the distance between supports (10,00 m) and the vertical loads, the beam has an elevated deflection, which implies visual problems and water penetration. For this reason, it was necessary to introduce a vertical support in the middle of the beam.

This support is made with a vertical glass pane of the façade. This glass is prepared to receive the vertical loads of the skylight, so it is thicker than the rest of the façade glasses.

In order to avoid the buckling problems of this glass due to its slenderness, this glass is glued with structural silicone to the lateral glazing units, that are situated perpendicularly, giving additional stiffness to the enclosure.

Figure 8. Section Details

78 | Intelligent Glass Solutions | Summer 2019

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD In the top assembly, the glass is supported on the steel beam, allowing the vertical movements, while on the exterior a horizontal bead is situated with an “L” shape, screwed to the interior steel beam.

The glass in the middle supports the upper beam and the skylight. For this reason the glass is thicker than in the rest of the facade. In this case, the glass is composed by three panes of 12 mm glass with 2 PVB between every glass pane. To ensure the support of the glass on the top, a steel screw is fixed between the glass and the beam.

In the skylight system, the glass beam is composed by a laminated glass of three panes of 12 mm tempered glass, with a stainless steel “T” profile glued in the top in order to support the horizontal glass of the skylight. The horizontal glass of the enclosure is composed by a double glazing. The exterior pane is a 8 mm exterior tempered glass with a solar control coating in face 2, and the interior pane is a laminated glass composed by two panes of 6 mm with 2 PVB. In between the two layers there is a gap with Argon to obtain a better thermal behaviour and to avoid the interior condensation. These horizontal glasses have in the perimeter glued an “L” shape profile of stainless steel in order to guarantee that the surface is watertight. This profile overlaps with an external cap made of stainless steel, with an “U” shape, that blocks water infiltration. In the joint with the existing building this “U” profile is changed with an “L” profile fixed to the existing frame, but also overlapping the “L” profile of the glass. In this area, in addition to the “L” shape profile, an EPDM membrane is glued between the different elements to have two barriers against water penetration.

In the exterior side of the skylight, between the glass and the new beam, an overlapped solution is made esto no se entiende. In this case, the upper glass of the double glazing overlaps with the steel beam to allow the flow of the water over it, avoiding water penetration.

On the transversal beams a steel rod is situated between the “L” shape profile of the glass and the “T” shape profile of the beam in order to fix both elements.

Construction process For construction there were two important subjects: • •

Total Budget Maintaining the whole building functioning at a normal pace

Due to these requirements the main works were to be undertaken during the summer. T In order to have prepare all the materials for the installation, the fabrication must be made based only in the drawings, it is not possible to have measurements on site, mainly the glass, because the fabrication time of curved glass is very long. To ensure that the dimensions of these

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Figure 8. Support detail

Summer 2019 | Intelligent Glass Solutions | 79

GPD FINLAND 2019 â&#x20AC;&#x201C; SHARING KNOWLEDGE AROUND THE WORLD glasses, some Wood templates were made and sent to the different factories (glass and steel), in order to guarantee a perfect assembly. All the elements, glass and steel were laser cut, and they were installed with topographical control.

Figure 10. Assembling of main beam

One of the most difficult actions during the installation was the correct placing of the main beam. The beam, 10 m width, was fabricated in 3 different pieces with different geometries, and should be assembled and welded on site, maintaining the total geometry of the beam. The setting out and welding was made on the floor, with the help of topographical instruments, and then the total beam was elevated to its position with 2 tackles situated in the ends of the beam, keeping the horizontal level of the beam through the whole process, to avoid deformations.

Before the elevation of the beam took place, vertical brackets were positioned on the structural slab coinciding with the existing windows frame. When the horizontal beam was placed, the ends were fixed over the previous brackets. To maintain the level of the beam until the installation of the vertical glass, some provisional post were situated in the middle.

Once the beam was properly placed, the horizontal support of the glass in the bottom was installed with the same geometry of the upper beam, to keep the vertical alignment of the glass enclosure.

Figure 11. Elevation of main beam

80 | Intelligent Glass Solutions | Summer 2019

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD Two sets of identical templates made in wood were sent to the glass manufacturer and the steel company, to make sure that both would fit on site. This allowed us to shorten the fabrication process.

With both the upper and lower structures in place, the most difficult action was undertook, loading the vertical glass. For this action the vertical screw on top of the middle glass was tightened to make contact with a horizontal stainless steel plate placed on top of the glass. This stainless steel plate was levelled over the upper edge of the glass with a self-leveling resin of Hilti with High strength. This resin allows the homogeneous distribution of the load all over the glass. When the screws were situated, the vertical tackles were removed and then the installation was concluded.

After positioning every structural element, the transversal beams of the skylight were installed with the horizontal screws, followed by the installation of the horizontal glass of the skylight.

At last the vertical glasses were installed between the bottom support and the upper beam, with the interior and exterior lacquered steel beams.

The vertical glasses were sealed –the structural vertical glass, in particular, to avoid the buckling of vertical glass. This sealing was made with structural monocomponent silicone of Dow Corning to be applied on site. This structural silicone was selected in grey color to minimize visual impact in the glass façade. The other sealings were made with watertight transparent silicone, and in the top and the bottom with black watertight silicone.

Figure 12. Loading vertical glass

Conclusion As a result of the processes involved in the project and the construction of the pavilion we learn some lessons: • It is not necessary have a big budget to obtain big architectural results • It is fundamental to know the way of construction while designing and developing the project, in order to adjust the constructive designs and technical solutions.

• The result of the project is better if all the people involved are engaged with the same objective.

• To obtain better results it is necessary that every element is designed at the beginning of the project.

• It is the development of technological solutions in big projects with big budgets, that might allow little projects to incorporate these technological improvements.

Acknowledgements Photographs by José Hevia

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Figure 13. Installation of vertical glass

Summer 2019 | Intelligent Glass Solutions | 81

GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD

The tallest, heaviest sliding Abstract Minimalist windows explore the potential of structural glass to provide large sliding glass doors with extremely thin doorframes.

Today’s architectural demands, dictated by the aim for transparency and spatial continuity between inside and outside, always push for better performances — more efficient and dynamic systems — and everlarger full-height sizes — with oversize glass panes often above the Jumbo dimension.

Large windowpane dimensions impose new technical challenges, requiring prior meticulous calculation and compelling each element to be re-engineered, and sometimes obliging appropriate machinery to be built for their installation. This paper focuses on this challenge, with ever-increasing precision in manufacturing and assembly to ensure glass panels to be operated with lightness and provide ease of maintenance, despite their size and weight.

Taking a 2015 UK-based residential project as a case study, this paper illustrates the challenges in terms of planning, engineering, supply and assembly of motorized 26 m2 double glass sliding panes 8m-high, weighing 3 tons each.

Despite the exceptional character of these limit situations, the problems raised by operating with massive elements are fundamental to raise awareness about aspects that are not so evident at a smaller scale or standard solutions, ultimately leading to improving products. Indeed, this customized solution formed the prototype for a new sliding door series, combining large glass sizes with strict thermal performance requirements, designed according to Minergie-P and Passivhaus standards.

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Carlos Machado e Moura1,2, Pedro Borges de Araújo1, 1 Jofebar / panoramah!® 2 Centre for Studies in Architecture and Urbanism Porto School of Architecture (CEAU-FAUP)

Keywords: Oversize glass • Sliding glass doors • Minimalist windows • Tempering • panoramah!® • Pringle Richards Sharratt Architects

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD

glass door of all: a case study Introduction So-called “minimalist windows” have known a remarkable success over the last two decades, taking advantage of the potential of structural glass to provide large sliding glass doors and windows with ultra-thin frames. The decision to use tempered glass — calculating its mechanical strength to play the role of the main component — and reduce aluminium profiles to mere finishing components, allowed the enlargement of glass surfaces, in tune with architectural demands, dictated by the aim for transparency and spatial continuity between inside and outside.

Over the last years, performance has been a significant driver in this field — continually pushing for higher efficiency and more dynamic systems — but also has size, with extra-large glass panes for full height doors and windows being required by architects for many residential projects, often with oversized windowpanes above Jumbo size. Large glass dimensions impose new technical challenges to ensure the panels can be operated with lightness and provide ease of maintenance, despite their size and weight. Their installation requires a prior meticulous calculation and, sometimes, the construction of appropriate machinery.

This paper’s case study, an UK-based residential project, allows focusing on this qualitative leap, with increasing precision in manufacturing and assembly and the challenges in terms of the design of motorised 26 m2 8 m-high double glazing sliding panes, each weighing 3 tons. [figure 1] By analysing the steps of preparation, supply and installation of this project, the article stresses the fact a considerable enlargement in size implies a full reengineering process, culminating in a different product with entirely altered components. However, despite their exceptional character, these experimental works are fundamental to test the limits of materials and to introduce a change of scale, compelling a vision that sometimes reveals possible improvements which are not evident in standard or smaller projects. This ability is perhaps their more relevant aspect, the way these projects contribute to improve the product and to create new opportunities and future uses. Indeed, this customised solution became the prototype for a new panoramah!® series, combining large dimensions with performance, specifically designed to respond to strict thermal requirements, meeting Minergie-P standards.

Figure 1

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Figure 5

Figure 2

Extra-large sliding doors and windows panoramah!ÂŽ had been developing extra-large window dimensions in aluminium sliding doors and windows over the years. Jumbo size glass panes, six-metre-high up to a surface of 19 m2, were used in several projects in India, namely the single glazed doors of a house in Juhu Beach (Mumbai), the most massive sliding windows ever built back in 2011 [figure 2]. One year later, also in India, a 7.2 m-high double-glazing was installed in another house in central Mumbai [figure 3]. The IGUs used on these projects fitted a series with 38 mm thick profiles. However, accommodating larger double-glazing dimensions or triple glazing required thicker profiles since the 38 mm thickness of the glass is limited to a maximum surface area of 7 m2 with triple glass units. The 38 mm series was therefore adapted to 54 mm in 2012, mostly by the introduction of polyamide elements in its profiles [1]. [figure 4] Projects with larger glass dimensions have used this series since then, reaching the size of 3 x 5.50 m tripleglazed panes, as installed in a villa in Switzerland [2].

However, a 2015 project for an environmentally friendly mansion designed by Pringle Richards Sharratt Architects in the Surrey Hills, to the south west of London, more specifically in a park in the Area of Outstanding Natural Beauty, challenged this limit and revealed to be an extraordinarily challenging and productive job [figure 5].

In the new house, two imposing courts act as giant lungs for the building moderating the environment in the environmentally closely controlled spaces arranged around them. The courts serve as both solar collectors in winter and repositories of cool night air in summer; from these spaces air, naturally tempered by a labyrinth of ducts in Figure 4

Figure 3

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Figure 7

the ground below the house, is circulated through the living and sleeping accommodation. The structure of the house is clad in locally sourced brickwork, the large roofs have a glulam structure and are clad in a bronze roofing system with integral solar thermal water heating system [figure 6]. Accordingly to Passivhaus standards, the house is designed to achieve Code for Sustainable Homes Code 6. These two courts around which the house is organised are introduced to the site in a manner that responds to the mature designed landscape and gardens and exploiting the rich topography and generating a wealth of external spaces and relationships between inside and outside [figure 7].

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD From the beginning the client wished the internal and external elements to blend and to bring the landscape into the house. The large openings and large uninterrupted panes of glass were essential in delivering this and the option for large openings to the courtyard south facing elevation was explored from very early on, the challenge was identifying a specialist company that would be able to deliver the ambitious requirement [figure 8: Main intro image]. Indeed, with two full-height glass doors with four double-glazing panes measuring 3.10 x 8.30 m and weighing almost 3 tons each, this project compelled panoramah!® to rethink a series of processes and procedures. Several other sliding doors and windows were installed in the house, one of which with an even larger surface of glass — 8.30 x 3.30 m, yet horizontal — sliding over the pool with a sill which functions as a vertical lift submerged gate between the interior and exterior pool areas [figure 9]. Despite these technical peculiarities, the full height 8 m sliding doors remain the most impressive and sophisticated feature of this work and the ones that paved the way for the engineering of a new series for installing large glass dimensions.

Planning and Engineering The composition of the DGU was carefully engineered to meet the needs for structural resistance. In particular, given the minimum dimensions of the door and window frames, covering the glass for only a few millimetres, excessive deformation could allow the glazing to come out of the frame under high pressures. Therefore, these large glass plates had to offer a maximum deflection of 36.5 mm for service wind loads around 1,050 Pa, which corresponds to 1/226 of the maximum glass dimension.

All glazing was tempered for more resistance and safety in case of failure. Furthermore, the glass had to be solar control coated to respond to thermal efficiency performance and extra-clear for aesthetic requirements. Therefore, the composition was determined as follows: DGU 19 mm tempered lowE coating + cavity 24mm with argon and a warm edge profile + 1212.4 tempered laminated.

The first challenge regarded the sourcing of the oversize insulated glass units. Back in 2015, several companies were able to manufacture monolithic tempered glass that large but not double-glazing units, extra clear glass, or adequately coated. Those requirements likely reduced the array to a single manufacturer, which formulated an offer for the job but was unable to specify a delay for delivery, as it depended too many variables and other manufacturers’ production. The company hired a specialised thirdparty consultant in Dubai to look for alternatives, who came up with three manufacturers. Despite the interest Figure 10

Figure 9

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD of those companies in performing the job, and complying with the technical requirements, only one was able to engage with a specific cost and delay. The company, based in China, was awarded and the glass units were manufactured in 3 months, as planned and according to the technical specifications, including a perfect flatness [3].

Also, although it was not strictly necessary, the glass was Heat Soak Tested (HST), as a complement of the tempering process, to eliminate glass carrying the risk of spontaneous breakage due to non-dissolved nickel sulphide inclusions. Despite this precaution — as mentioned afterwards — one of the glass panes broke after installation given the presence of a rare chemical element not yet covered by norms. To reduce the risks associated with shipping, packing and handling these oversize units, the U-channels structural bonding to the glass was done in the glass manufacturer factory by Portuguese panoramah!® teams, which travelled to China and had the support of an interpreter. Overseas freight transport was afterwards organised directly from China to the UK, requiring special transport operations both by sea and ground, with on-deck shipping and specialised trailers.

The second step of development regarded the engineering and manufacture of the aluminium elements of the frame, and the reinforcement of a series of components.

Although initially, it seemed a task of adapting a sliding door structure to a larger dimension, in the end, no element of the original window remained in this specific solution [figure 10]. 8 m long profiles are complicated to produce as 6.5 m sets a pattern size for aluminium extruFigure 11

sions, possibly according to transport dimensions [4]. Indeed, in this case-study, special extrusions with stainless steel reinforcements, aluminium tempering and anodising had to be performed in three factories, located in different places of Spain. Elements this size are often used in the aeronautical industry, but seldom in the construction sector, and generally with aluminium leagues which are not anodisable. Therefore the treatment companies that regularly collaborate with panoramah!® were unable to provide both a tempering furnace and an anodising tank large enough for these profiles. They were bronze anodised, with some elements powder coated with a similar RAL, and their final transformation was done afterwards in Portugal.

The frame’s aluminium profiles were enlarged with polyamide elements — as previously done in the 54 mm series —, to accommodate the thickness of the DGU. However, the previous experience had revealed that the impact of heavy glass during installation shattered the polyamide bridge on the sill. Therefore, although it compromised thermal break, the sill incorporated a stainless steel element beneath the polyamide bridge to protect it, since the first stages of development. However, polyamide was still damaged after testing, rendering inevitable a solution with a solid stainless steel profile and a different polyamide bridge, to minimise its thermal conductivity [figure 11]. To ensure the perfect planarity of the sill — determinant to achieve light operability of the sliding panes — a preframe was installed underneath the structure with a thick metal tubular profile. Given the weight of the unit, aluminium shims replaced the standard PVC ones, with a reduced distance between them (20 cm instead of regular 30 cm). Furthermore, the sill was mechanically anchored to the underneath preframe to ensure safety [figure 12]. Generally, minimalist systems avoid this solution as screwing inferior elements might compromise waterproof-

Figure 12

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GPD FINLAND 2019 â&#x20AC;&#x201C; SHARING KNOWLEDGE AROUND THE WORLD ing. Therefore a different system was developed and adopted, using the tubular preframe as a watercolumn and implementing separated water channels to minimise risks and provide more efficient drainage. Additionally, customised mullion and pull-handle covers were adapted to eliminate any possibilities of water penetration through handles and glass lids.

Vertically, stainless steel components (228 mm long 8 Figure 13

mm thick) reinforced central mullions internally to sustain the glazing weight and resist wind loads. These were also adapted to create a more significant gap, ensuring no friction on the adjacent glass panel when sliding, if it is subject to a considerable deflection, something likely to occur in large glass panes. Roller bearings had to be carefully chosen and combined to operate such massive glasses, increasing to the triple of their standard dimension, as the first attempts â&#x20AC;&#x201D; with ball bearings, plain bearings, needle roller bearings, cylindrical roller bearings, etc. â&#x20AC;&#x201D; broke due to the weight. Also, the motors were upgraded to more performant ones. Indeed, the significant distance between the roller bearings in the sill, and the engine on the top created a considerable momentum at the start movement, impeding soft progress and forcing the structure of the building. Only a more powerful motor equipped with chains instead of ordinary belts and a carefully determined number of fixations of the engine to the door were able to respond to this question [figure 13]. These and many other decisions emerged from tests performed in a metal factory mockup with the same geometry and weight of the sashes, which ran the motor for a series of 15,000 test cycles [figure 14]. The last change regarded the location of the safety sensors, which were placed laterally, instead of the standard bottom and top position since the vertical distance could compromise their effectiveness.

Figure 15

Figure 14

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Installation The installation process proved to be a challenge as complex as the preparation.

Besides the calculations required to determine the safer way to carry the structure to the building site through existing road infrastructure,

Figure 16

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD with a route involving narrow roads and sharp bends, several accesses had to be specially adapted for this transportation. A bridge was reinforced, and the paths which led to the site were covered with thick metal plates as the trucks weighted more than the road could sustain.

Additionally, the soil composition of the garden dictated the position of the crane by the rear façade, opposite to the operations [figure 15]. Only two companies were able to provide glass lifters robust enough for moving each 3-ton glazing panel. Furthermore, their machinery had to be adapted with 16 suction cups to lift and move elements of this dimension [figure 16].

The factory mockup allowed previous training of the team and the determination of the most efficient way of installation. However, especially given the fact that the process took place in October in the UK, atmospheric conditions and daylight had to be taken into account as well.

Operations could not take place under rain or wind, each sash installation took over 1h30 and each crate contained two panels. Therefore, the decision to assemble each panel had to be well pondered, guaranteeing the conditions were met for two installations. The eight sashes were finally installed after two and a half days of work. [figures 17, 18, 19, 20, 21, 22] Risks involved Whereas in the case of traditional windows, component sourcing and assembly can generally be confined to a relatively reduced geographic area — extrusions, glass manufacture and aluminium treatments can be assured by local suppliers — with oversize windows the opposite occurs. These involve a unique work and a very disperse supply chain, with several components manufactured by a single or very particular companies, resulting in a much more complicated process involving risks which are extremely difficult to calculate.

In this case study, the installation of glass doors near London was commissioned to a Portuguese company, involving special aluminium extrusions and anodizing in Spain, transformation in Portugal, glass manufacturing in China via a Dubai consultant, U-bonding in China by Portuguese teams, specialized transportation to the UK, reinforcements in the accesses to the building site, adaptation of installation machinery, etc. This complex supply chain, with all the details regarding predictable and unpredictable aspects, renders this project’s risk very high.

Indeed, despite all the precautions with risk identification and mitigation, several issues are still not foreseeable. An excellent example of hidden risks is the HST test performed to dismiss the dangers of spontaneous breakage after installation. Orientating numbers for breakage rate in a typical HST are around 1%. However, this number is determined with reduced glass surfaces whereas in large glass panes like this case study’s the probability of critical inclusions is by far superior. Furthermore, the average

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Figure 17

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GPD FINLAND 2019 â&#x20AC;&#x201C; SHARING KNOWLEDGE AROUND THE WORLD considers glass from many different furnaces, while in this case all panes are manufactured in the same furnace, whereas an unfortunate combination of factors might render nearly all glass production defective. Despite all the precautions with choosing the most technologically reliable solution and performing HST testing, one of the glass panes broke after installation and had to be replaced. Analyses later confirmed that no nickel sulphide inclusions were present in the broken glass, but revealed an extremely rare chemical element that has not yet been studied and therefore no norm presently covers this phenomenon.

Given their exceptionally high risk, these works require very high prices, incomparable with the range of any other standard product. In 2015, this project corresponded to state of the art, with the best glass and components available and a client that was willing to take the risk and to pay for having this unique solution at home.

Figure 19

Lessons learned, new opportunities and future developments Above a certain dimension or configuration, one can hardly distinguish between a window, a door and a sliding glass wall. These projects challenge materialsâ&#x20AC;&#x2122; limits and require extreme care during all stages of development and assembly, revising a series of procedures, especially

Figure 21

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD those often neglected in more traditional solutions.

Indeed, what initially seemed a task of adapting a sliding door system to a more massive structure, revealed at the end to have no component of the original window being used in this solution. However, these works are fundamental for testing the limits of materials and measuring the state of the art technologies.

The first attempts at installing large sliding glass doors in India revealed the difficulties and the limits of the system. Back in 2011, in the Juhu Beach house project, 1919 tempered laminated six-metre-high panes had a considerable deformation, as the existing technology hadn’t yet achieved the level of perfect flatness of the 2015 UK case study. This irregularity, combined with the weight of the glass, shattered and torn the polyamide profiles and damaged roller bearings. Furthermore, aluminium composite extrusions reinforced with high strength stainless steel supporting elements were not yet available, so all reinforcements were done in an artisanal way, with bent steel plates additions and complicated bonding, which resulted in the window to operate unsmoothly and to require adjustments after installation. In 2012, the industry was getting ready to transform oversized glass panes, and the 7.2 m doors of the other Mumbai house were already double-glazed, although the sealed unit was still manually manufactured and assembled. By 2015, when panoramah!® installed the UK 8 m-high glass doors, the previous experience of these two projects and others — ranging from 5.5 m to 6 m high doors — allowed to optimize several procedures: better extrusions and reinforcements, hybrid fixations combining mechanical assembly and bonding, testing different roll bearings gauges, combination of solid elements with water jet and laser cut parts, etc.

Therefore, with this experience, conditions had emerged to conceive and produce a new series of sliding doors and windows, optimised to resolve many of the questions raised in large sliding panes. The new series renders much easier the installation of glazing around 20 m2 per pane in double-glazing. Maximum surfaces can theoretically go up to a maximum of 29 m2 and triple glass units up to 19 m2 per panel — although with a more complicated installation — while maintaining 20 mm vertical profiles: an exponential surface growth achieved only through the reinforcement of the frame. Instead of enlarging current aluminium profiles with polyamide elements as performed before, the engineering of the new 60 mm thick series altered significantly their section, changing the position of the polyamide profile — now between each rail instead of being placed in the axis of each track — in a way that it ensures a very efficient thermal break [figure 4].

Many of the problems raised in previous works that were particularly stressed in projects like this UK case study could, therefore, be eliminated in this new panoramah!® 60 series. Among the issues that were better understood

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and improved, we could stress three. The relevance of the stiffness and perfect planarity of the layer under the sill, with no deformations, is fundamental to ensure ideal operability of the sashes even with motorization. Care with this issue had been a significant concern in the first minimal windows installations but had progressive been neglected as the evolution of the product and the improvement of its various components rendered it less perceptible. However, the larger and heavier the panes are the more evident this aspect becomes. A second aspect relates to air and water tightness. So far, improvements on water tightness tended to render air tightness less effective and vice-versa. With the need for altering the water column and the drainage system to screw the sill to the underneath structure, both air and water tightness were significantly improved. A final but central aspect that was carried to the new series regards the redesign of the central mullion. Its more significant gap between the two sashes allowed to prevent friction in the other sliding pane — something that occurs with the deflection of oversize or not so large square-shaped glazing — but also to eliminate possible thermal transfers by radiation.

Together with the improvements in the frame and the new position of the polyamide profile, this contributed to significantly improve the thermal performance of the new series, awarding it a Minergie-P certification.

This comes to prove those limit situations are crucial steps to develop better products, imposing a shift of scale that raises awareness about aspects that are not so evident at a smaller scale or standard solutions. Somehow Verdi’s motto that you need to step back to move forward [5] seems particularly accurate.

References * The title of this article is a deliberate twist at the song “The Biggest, Loudiest, Hairiest Group of All” by The Velvet Underground.

[1] Developed by panoramah!® for Villa NHV in Vandoeuvres (Geneva, Switzerland), a dla designlabarchitecture project. The new 54 mm series, quickly became the most award-winning minimalist series, with Minergie and Passivhaus certification for improved thermal performance.

[2] Villa D in Vaud (2015) designed by architect Grégory Garcia.

[3] Yet 50% of the manufactured glass was wasted: 9 oversize glasses out of 13 were discarded for being defective; therefore the total glass manufacture for these doors was 22 panes.

[4] Trucks with 13.5 m-long capacity can carry two charges of 6.5 m profiles, while sea transportation sets a 5.80 m limit with 22-foot containers.

[5] “Torniamo all’antico e sarà un progresso”, as wrote Giuseppe Verdi in a letter to Francesco Florimo in 5th January 1871.

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The Next Step in Digital design and fabrication. By Lenk, P., Vitalis, D., Abstract Evolution in the design is now in the digital space, where a myriad of permutations can be processed in seconds and optimal options identified. Digital workflows, hand in hand with digital fabrication, are certainly on the minds of many engineers in the construction industry.

In this paper, we will expand on our current research looking into composite glass structures. We will focus on how to improve parametric design and generalize workflows. We will research possibilities in current digital fabrication techniques and identify possible methods applicable in structural glass and adhesives. Investigating the possibilities and limitations of digital fabrication in the construction industry could lead to an increase in fabrication tolerances, safety and productivity as currently labour-intensive techniques are dictating the cost of many innovative solutions. A case study of a glass/glass hybrid panel, developed with TU Delft for the Glasstec fair 2018 in Dusseldorf, will be discussed in the context of other past and current Arup projects to demonstrate current digital design advances. The glass/glass composite panel can enable us to design bigger spans while preserving natural resources which is another increasingly pressing parameter influencing our current designs.

Introduction Organic forms have been inspirational for designers since the beginning of time. However due to the geometrical complexity of the natural form, simple rules of thumb and grids were introduced in architecture to increase its efficiency and feasibility.

However, such constraints may hinder design evolution and be detrimental to architectural creativity.

Similarly, our engineering principles are based on simplified assumptions due to the low variability of components and the high repetition of the structural systems.

We are now on the brink of a new digital era. Our technologies and understanding of systems allow us to experiment with forms and shapes more effectively than ever. It is therefore clear that there is room for improvement in trying to achieve the free form structures we envisage. The authors strongly hold that new technologies can help us design efficient and optimised structures with the aim to reduce material consumption, fabrication time and costs, and finally explore new architectural expressions. This paper investigates state of the art methods of digital design and digital fabrication with glass and aims to propose ways of seamlessly combining the two to achieve a desirable result.

Figure 1. Organic forms, a.) bone structure, Pearson Education b.) leave structure, c.) glass molecules â&#x20AC;&#x201C; computer generated image

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Structural Glass Digital Design [Bejan A , 2000] considers the design and optimization of engineered systems and presents a relationship to the generation of geometric form in natural systems. He argues that the objective and constraints principles in engineering are the same mechanisms underlying the geometry in natural systems. Evolutionary and randomized statistical algorithms like Galapagos and Monte Carlo were successfully deployed to optimize solutions in many engineering problems.

Current engineering practice is presented with the challenge of having to go through multiple permutations and assess their feasibility in real time. Parametric software has given us the opportunity to efficiently and effectively incorporate the extra step of structural engineering into the design process. With software such as Karamba, we can automatically carry out a preliminary assessment of the structural behaviour of a certain permutation.

However, in the construction industry the flow of information is not smooth. The design tools are usually not centralised and therefore cannot be used by all collaborators and certainly not throughout all stages. Hence, design workflows need to be carefully planned and a central platform to exchange information should be defined. Only then will the process be automated to such an extent that it will positively influence the design process.

The main difference between the way we design today and the way we used to design is that new tools are incorporated into the design process transforming an otherwise static procedure into a dynamic workflow. Twenty years ago, the designer would sketch an idea, CAD it up, carry out the structural analysis, check the design against other requirements such as movements, tolerances etc in a very linear workflow. If validation could not be achieved in one of those steps, the process would have to go back to initial sketching. Nowadays, we are given the chance to design a workflow that can instantly check the design against performance requirements or even optimise the design based on those parameters.

Glass design can easily fit into this trend and the authors cannot see any major reasons why current trends could not be fully deployed in our industry. Many scripts helping with design of geometrically complex glass envelopes

Figure 2. a.) (above) Digital design project application â&#x20AC;&#x201C; Coal Drops Yard, London, b.) (inset)design workflow

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GPD FINLAND 2019 â&#x20AC;&#x201C; SHARING KNOWLEDGE AROUND THE WORLD have been employed in the past and will continue to be employed e.g. checking glass warping and sub-sequential stress in glass and other components, analysing climatic loads in curved panels were presented by [Marinov, V, Griffith, J, 2015] and near future possibility to use AI by [Griffith, J, 2017]. However, while parametric tools have been continuously introduced in the design process, generative design with glass as the main structural material poses significant challenges. Glass is different from other materials due to its brittle nature. Peak stresses can therefore be detrimental to the behaviour of the structure and support conditions must be carefully modelled on a case by case process. This makes the use of universal scripts more difficult. Finally, glass as a material is normally used in planar elements the structural calculation of which typically requires a FEA. This is normally expected to slow down the design process making the use of generative scripts more challenging.

Digital Fabrication If we were to simplify the architectural manifestos of the 20th, the concept of fluidity has always been a divisive term. There were movements which embraced fluid shapes and other movements which alienated themselves from organic forms. It is well established that new architectural movements derive from a need to contrast the past, and to explore the undiscovered. The movements of Arts & Crafts and Art Deco introduced the concept of seamless architecture. This architectural expression would require highly skilled workmanship and a significant amount of manual work. This came as a reaction to the industrial revolution and the need for mass production. This was later challenged by modern architecture which in turn was challenged by the post-modernists.

There always seemed to be a contrast between the mass produced and the bespoke. But what if something could be bespoke and mass produced at the same time?

Figure 3. From left clockwise: traditional glass crafting, MIT casted glass example photo: James Griffith, AI Built, robotic arm printing PLA

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GPD FINLAND 2019 â&#x20AC;&#x201C; SHARING KNOWLEDGE AROUND THE WORLD Fabrication techniques are divided into three main categories: a) forming, b) cutting, and c) joining. Each of these have opportunities for glass which are briefly explored below.

Forming Additive manufacturing 3D printing is available from a limited number of sources worldwide. At present, it is costly but has the potential to open the door to unlimited design options. Research resources are dedicated into investigating the molecular behaviour of 3D printed glass and therefore its mechanical properties.

Subtractive manufacturing 3D milling of glass is a relatively new process which is commonly used to give glass some texture. The fact that milled glass may lock in residual stresses makes it challenging to link this process with generative design as an intermediate step of detailed FEA should be introduced.

do exist, and DGU assembly lines form part of most advanced glass manufacturing facilities. However bespoke project specific glass processing, as well as site installation, are still heavily dependent on manual handling. Not all fabrication processes are available in glass manufacturing and certainly not all of those listed can be considered to be digital.

Case Study Digital design and fabrication are expected to enhance the efficiency of our work. Arup, in collaboration with Delft University of Technology and SCHOTT, designed and built an all-glass sandwich panel. The panel was exhibited at Glasstec 2018 as a floor, to demonstrate the potential of composite glass structures in structurally demanding applications. The aim was to design a panel that would have high bending stiffness while minimising material

Shaping 3D shaping glass is the oldest known way of forming glass. Glass can be kiln formed or cast in 3D shapes. However, methods of 3D shaping require the use of a mould.

Hence, repetitiveness and manual work are still required and therefore the method is inherently non-digital.

Cutting Glass can be easily manipulated if heated up. The authors do not see any technical reason why the glass industry cannot embrace cutting technics such as die, punch or shear cutting etc.

Joining Adhesives Adhesives are commonly used in structural glass applications and range from stiff and brittle acrylate-based to flexible and ductile silicone-based. This is where the authors see the maximum potential of digital fabrication. Industry is currently exploring ways of 3D printing adhesives which is expected to provide a fertile ground for glass fluid shapes to grow.

Mechanical and Fusion/Welding At present, the process of fusing glass is completely manual and consumed in artistic applications or in glass blowing laboratories. There is high potential in bringing this method into the digital era as its labour-intensive nature is currently keeping it away from the digital transformation.

In conclusion, the glass industry has been exploring the digital world and, in some areas, is well advanced: automation of manufacturing processes is relatively well evolved, automated glass production and processing lines

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Figure 4. Parametric workflow

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Figure 5. Finite element verification models consumption. To achieve this, parametric design methods were employed.

Composite structures typically consist of three main elements: a) two skins, b) a structural core and c) an adhesive layer between. The thickness, the type, the geometry, and the mechanical properties of these constitute design variables. Hence, the design of a composite panel involves several quantifiable parameters that feed into a composite mathematical function. To contain and rationalise the problem, early design decisions were made based on aesthetical constraints. The properties of the skins were defined by means of homogenisation of the section (EI=Eâ&#x20AC;&#x2122;Iâ&#x20AC;&#x2122;); a double glass laminate with 10mm HS glass was used for each skin. Borosilicate glass tubes were used as spacers to provide support to the skins. This spacer was deemed ideal for exhibition purposes as it gives the maximum design potential. Then acrylate adhesive was used to bond the core elements to the skins.

In general, in order to optimise material usage the best balance can be found between the remaining variables: core thickness and distribution of spacers within the core.

The final pattern was defined using Karamba/Grasshopper/Rhino. The pattern was optimised in such a way that

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shear forces on the beam elements (spacers) are constant across the whole length of the panel. To achieve this, the pattern of the flow of the shear stresses in the plates was printed and spacer elements were placed in the intersection between this pattern and the pattern of the global shear forces. The approach was similar to the distribution of shear studs in steel-concrete composite beams.

The digital workflow was completed by a detailed FEA using Strand7. The adhesive connection between one glass spacer and the glass skin was modelled with brick elements. The resulting connection stiffness fed back onto the parametric model in the form of nodal rotational stiffnesses to further refine the pattern. In short, the above described process yields an optimised and therefore efficient result which achieves the maximum stiffness to weight ratio. The real benefit of this application is that once those constraints are set, the design script is available to instantly churn out numerous structurally validated results based on changing loads and boundary conditions. The downside is that the resulting pattern comes out of an intricate computational process and therefore is not orthogonal and as such it poses fabrication/assembly challenges.

For the construction of each panel, 150 spacers were required and those had to be manually placed and glued.

This process was time-consuming, labour-intensive and required rationalisation of the pattern leading to an increase in the number of spacers by 30%. This suggests the barrier between digital design and fabrication is sometimes prohibitive when it comes to real innovation and optimisation.

In other industries e.g. automotive, furniture etc. robotic fabrication is fully embraced. One could argue that the difference between those industries and the construction industry is that in the built environment, most endeavours are bespoke and therefore any economies of scale are applicable only within the strict boundaries of a particular project. Contemporary architecture is leaning towards organic and intricate shapes with minimum repetitiveness. This new architectural language suggests that structural glass applications could certainly benefit from a seamless transition between digital design and digital fabrication.

In this case, the positioning of the spacers at the right location within the core could have been achieved with a robotic arm and the appropriate end-effector. Parameters related to the precision of a robot movement e.g. spatial resolution, accuracy, and repeatability are well within the range of tolerances typically provided in the construction industry and are therefore covered by relevant safety factors. Furthermore, a digitally controlled application of adhesives would also be beneficial for this application.

However, the precision required for acrylate adhesives cannot be achieved with existing means without postprocessing of the joint.

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Figure 6. final product, below: detail view, above: view of the assembly

generative design, digital design is essential in glass design as it significantly assists in accommodating intricate geometries, exploring different support conditions, and generally going through multiple design iterations. Other industries make good use of digital tools. A very good example of effective use of a digital design to fabrication workflow comes from the furniture and industrial design industry. The Breeding Tables designed by [Kraam, Weishaar, 2005] constitute the perfect example of how mass customisation can be achieved using genetic algorithms. What if we could use the same tools and principles to design and fabricate glass structures with the click of a button?

Acknowledgment TU Delft Glass & Transparency group, Prof. Rob Nijsse, Dr. Fred Veer, Faidra Oikonomopoulou, Graham Dodd at Arup for his support and comments & James Griffith for photographs 2a.) and 3b.)

While the built environment is shifting towards solutions that promote sustainability, together digital design and fabrication can guarantee more efficient use of available resources without putting architectural innovation in jeopardy.

Conclusion The trend towards complex engineering systems, especially in geometry, is noticeable. Architecture has moved to digital space where manipulating complex geometrical forms is as easy as it was defining rectilinear orthogonal building structures on the drawing board in the past. When heatchanged to fluid, glass allows us to manipulate its shape relatively effortlessly. This mechanical property is a great advantage and could be used in digital fabrication.

Even though the high level of complexity of structural glass applications does not provide a fertile ground for

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References [1] Bejan, A., 2000, Shape and structure from engineering to nature, Cambridge University Press 344 pages (ISBN 0-521-79049-2) [2] Marinov, V., Griffith, J 2015, Optimisation of curved insulated glass In GPD 2015, Finland 2015 [3] Griffith, J., 2017 Applied machine learning in structural glass design In GPD 2017, Finland 2017 [4] Kraam, R., Weisshaar, C., 2005, http://www.kramweisshaar.com [5] Thompson, R., 2007, Manufacturing Processes for Design Professionals [6] Kolarevic, B., 2003, Architecture in the Digital Age: Design and Manufacturing [7] Lefteri, C., 2007 Making it: Manufacturing Techniques for Product Design

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Innovative glass bending technology for manufacturing expressive shaped glasses with sharp curves Tobias Rist1, Matthias Gremmelspacher2, Adrian Baab3 1 Fraunhofer Institute for Mechanics of Materials IWM, Wöhlerstr. 11, 79108 Freiburg i. Br., tobias.rist@iwm.fraunhofer.de 2 Fraunhofer Institute for Mechanics of Materials IWM, Wöhlerstr. 11, 79108 Freiburg i.Br., matthias.gremmelspacher@iwm.fraunhofer.de 3 Fraunhofer Institute for Mechanics of Materials IWM, Wöhlerstr. 11, 79108 Freiburg i.Br., adrian.baab@iwm.fraunhofer.de

Keywords flat glass bending process, bent glass with very small radius, insulating glazing Abstract Three-dimensional formed glass products, manufactured from flat glass, are experiencing rapidly growing demand. Actual limitations of bent glass products are shapes with sharp curves, meaning bending radii smaller than 50 mm are not available. Within this work, we present an innovative and advanced bending process for manufacturing sharp curved glass. Using this technology designers and architects are able to create expressive shaped glass shells for products and buildings. We use a special glass bending facility to apply local heat to the glass. Numerical simulations with an advanced material model and a detailed description of the thermal conductance and temperature distribution are performed during the development phase. Real samples were formed to demonstrate the potential for the use in modern façades and automotive applications.

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Introduction Glass is a fascinating material which plays an important role in architecture. Due to its characteristics, being transparent or translucent it controls the incidence of light into the building. Besides it is also reflective, may be colored, has gloss, so it lends buildings to an extraordinary aesthetics from the outside.

There is still potential to increase the combination of design and functionality through individual and special glass designs. Architects and builder-owners go in for high optical quality demanding glass with low waviness and without defects like imprints. Ideally the glass products are manufactured ready for installation, have precise geometrical fittings, are free from interruptions and provide high and constant level of thermal insulation to make sure that the heat transition along the window front has little variations.

Glazing around the building’s corner up to now uses glued or post and beam constructions. These solutions have nontransparent areas caused by non-glass elements such as spacers or beams at the corners, see figure 1. Apart from the visual impression with interrupted transparency, controlling of the heat flux in the corner areas is technically challenging. High gradients of thermal conductivity hold the risk of condensation, which can cause mould formation, especially problematical at glued lines. A full glass corner could be an elegant way to avoid these problems.

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Figure 1. At the top: cross sections of different insulation glazing configurations, schematically.

At the bottom: View through the above glazing, modeled in CAD. Configuration a. and b. represent common glued corner insulation glazing taken from [1]; configuration c. represents the insulation glazing demonstrator from Fraunhofer IWM.

Bending process At Fraunhofer IWM, glass bending processes have been developed for forming sheet glass especially with application of local heating. These processes have several advantages compared to conventional bending processes. Nonisothermal processing of the glass with “hot” and “cold” areas within the glass sheet enables handling, fixation and supporting of the glass body at the “cold spots” far away from the “hot spots” of the softened glass material which is to be bent and remodeled. As a result the quality of the bent and the flat areas are at a very high level.

Shapes with flat areas retain the very high surface quality of the origin float glass concerning flatness and waviness

as the flat areas will not be deformed at all during the glass bending process. Besides, applying precise, concentrated and well-defined local heating enables pronounced shapes with very small bending radii, whereby shapes can be realized that have never been formed in glass before – some examples are shown in Fig. 3 and Fig. 5. Glass sheets up to 1m x 1m can be processed inside the research glass bending machine at the Fraunhofer IWM in Freiburg.

Local heat is applied by a high power laser in combination with a laser scanner enabling any path to be scribed on the glass. During the process local heating is controlled by laser energy and laser path kinetics imposed by the laser scanner program. This yields to an enormous flexibility

Figure 2. Left: Scheme of a bending set-up to perform a 90° shape with different bending radii according to the width of the heat zones b1 and b2, from [2]; right: simulation of bending process, colored is the temperature field.

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD concerning process guiding. For example, bending a glass sheet to a 90 degree corner, the width of the heated zone and the intensity along the heat zone can be adjusted to customized requirements, figure 2. By these parameters, laser power and laser duration, the bending radius and the bending angle can be controlled precisely.

The laboratory bending machine is additionally equipped with an infrared-camera, allowing the researchers to have a look onto the glass sheet inside the furnace and to measure and register transient local temperature distribution. These data are used to improve the bending process.

However, to optimize such bending processes is a multi-parameter challenge. State-of-the art procedure to cope with these challenges is to rely on the experience of glass specialists. At Fraunhofer IWM we also make use of numerical simulations based on finite elements method to simulate glass material behavior throughout the heating cycle and the bending process [2], figure 2. In

current projects we are working on advanced automated and intelligent workflows to support the optimization by using simulation methods and machine learning tools and algorithms.

Expressive shaped glass products, examples and demonstrators Several different shapes have been formed by using this method. The examples shown below, demonstrate the feasibility to form geometric outstanding shapes, figure 3, and also show possibilities to apply the formed glass to products or complete systems made of bent glass.

Shapes like the round plate and the semi-circle in figure 3 have inspired design students to create a building façade with functional “bubbles”, figure 4. The virtual building created by the design students of the Hochschule München has a vertical flat and translucent façade which lets sun light pass dazzle-free but prevents people standing outside of the building to look inside it. People

Figure 3. Experimental examples from laser-enhanced sheet glass bending.

Figure 4. Virtual building with functional glass façade.

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD from inside of the building can look through the translucent glass. The “bubbles” have two functional areas: the flat transparent areas allow people from the inside of the building to have a clear look to the outside, and allows indirect light from the environment to come in. The curved areas are nontransparent and prevent direct sun light to shine into the building. This ensures a pleasant atmosphere and helps to regulate the temperature inside.

The second example uses sharp bent glasses as basic elements. Using the above described technology glasses can be sharply bent to defined radii. Figure 5 shows three glasses of thickness 3 mm, each bent to 90° angle but with different radii, i.e. 5, 10 and 20 mm radius respectively.

Such glasses can be used to build full glass corner insulation glazing like the one shown in fig. 6. Sharp edged bent glass insulation glazing have the potential to substitute glued corner insulation glazing which is used up to now.

Furthermore, from single bent glasses with compatible radii, i.e. the inner radius of the outer glass is equal to the outer radius of the inner glass plus film thickness, laminated safety glass can be manufactured for various implementations.

Discussion and outlook The combination of experimental tooling for laserassisted sheet glass bending and numerical modeling of the heating and bending process leads to new horizons for glass façade design in architecture and other fields.

Research work has created an enabling technology for producing high optical and geometrical quality at high production rate suitable for mass production as well as for manufacturing individually customized shapes at single piece batch size.

This bending process was designed in the first place for processing of soda-lime silicate glass, i.e. conventional float glass, of various thicknesses and various coloring. As preliminary experimental tests have shown, this process may also be applied to glasses of different compositions like borosilicate glasses (e.g. Borofloat®), aluminosilicate glasses (e.g. Gorilla®), glassceramics (e.g. Robax®). Results from such experimental studies are described elsewhere [3].

Acknowledgments The authors thank Johanna Duebener and Teresa Naujokat for performing the design project, including the creation of the 3D-models of the virtual building.

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References [1] Siebert, B.: Glasecken mit tragender Verklebung. In: Weller, B.; Tasche, S. (eds.): Glasbau 2019, Dresden 2019. Berlin: Wilhelm Ernst & Sohn, Verlag für Architektur und technische Wissenschaften GmbH & Co. KG 2019, p. 33-43; https://doi. org/10.1002/cepa.997 [2] Rist, T.; Gremmelspacher, M.; Baab, A.: Feasibility of bent glasses with small bending radii. In: Weller, B.; Schneider, J. (eds.): Engineered Tranparency; glasstec 2018, Düsseldorf 2018. Berlin: Wilhelm Ernst & Sohn, Verlag für Architektur und technische Wissenschaften GmbH & Co. KG 2018, p. 235241; https://doi.org/10.1002/cepa.921 [3] Rist, T.; Gremmelspacher, M.; Baab, A.; Manns, P.: Sheet glass bending enhanced by IR-laser radiation. Glass Struct. Eng. 4 (2019) to be published; http://www.springer.com/40940

Figure 5. Bent glasses with 90° angle and bending radii 5, 10, 20 mm.

Figure 6. Demonstrator of a 90° full glass corner insulation glazing (left) and stateof the art glued glazing (right).

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Essential - Inspection of Glass Facades Barbara Siebert Dr. Siebert Consulting Engineers, Munich, Germany Abstract Modern architecture continues to produce ever more attractive and higher quality façade constructions. In previous years façade design and construction was predominantly based on experience. In leu of the complexities of modern-day facades, sophisticated structural analysis is often a necessity when it comes to design. However, structural design is often negated due to inadequate knowledge in this field. At present, we see damage to old facades but also to new constructions. These problems are proliferating and sometimes culminate in collapsing façade elements.

These concerns also apply to high rise buildings in which the requirement of precise structural façade design is paramount. Firstly, this paper will present several problems that facades are typically subject to. These complications are evident in several facets of the façade process, including analysis, design, execution and regulations. It was also found that inspection of hidden parts (brackets or gluing) becomes more essential. The fundamental aspiration of this paper is to present a framework for monitoring façade design and construction in order to invalidate the atypical problems that will be outlined. The first results are presented in this paper.

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Introduction There are a large number of facade variants with regard to material, design and fastening. Aluminium, glass and plastics are used in ever-increasing element sizes.

Single facades, double skin facades, element-facades are common. In addition, variants in fixings: linear, in points, glued with specialized silicone or hidden on the back of elements, are prominent in façade construction. Glass as a transparent building material allows the natural lighting of rooms. Essentially, this reduces lighting energy costs while also conferring additional benefits to workplace productivity and well-being. In light of ever more complex façade construction – there is increased risk of complications in the lifespan of a building. Subsequently the monitoring of defects, at all stages, including its renovation, has become more important.

Regulations for Inspection After a significant number of tragic building collapses in Europe at the start of 2006, a new guideline was introduced in Germany. With the publication of “VDI 6200: Structural safety of buildings – Regular Inspections”, a succinct framework for the inspections of buildings was made available. VDI 6200 contains assessment, evaluation criteria and practical instructions for the regular inspection of structural safety as well as recommendations for the maintenance of a multitude of building types (with the exception of traffic structures). Building constructions are classified according to the possible consequences in the event of global or partial failure and their structural design. However, it is not commonly known that the guideline should also be applied to facades. According to the guideline, facades are classified in damage-impact class CC2, the same class as high-rise and public buildings. Class CC2 pertains to medium consequences, that may result in damage to the life and health of many people and serious environmental damage. Furthermore, robust classes RC1 – RC4 are described in the guideline. These damage-impact classes form the basis of Eurocode 1.

Depending on the Consequences class, intervals for periodic inspections are given as orientation values (see table

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Intervals for periodic inspections according guideline VDI 6200

Consequences Class

Surveillance [years]

Inspection [years]

Thorough examination [years]

CC3

1 to 2

2 to 3

6 to 9

CC2

2 to 3

4 to 5

12 to 15

CC1

3 to 5

As required

As required

1). Regarding class CC2, the owner or authorized representatives should perform surveillance of the building every 2 to 3 years to look for obvious defects or damages and produce a report thereafter. In addition, every 4 to 5 years, inspection by an expert should be completed and every 12 to 15 years a thorough examination. This includes parts of the structure that are difficult to access. It may be necessary to take material samples to determine the remaining strengths and rigidities. Furthermore, any defects or damages found must be assessed in terms of their significance to the overall structural safety of the building. Complications arise when attempting to apply this framework of inspection to façade construction; specifically with regards to the “examination of parts of the structure, which are difficult to access”. The examination of fixing points of an element façade often means the complete dismantling of the façade.

Common faults and methods of examination and monitoring Glass In case of Glass facades, it is relatively simple to check glass-thickness with specialized measuring equipment.

In cases where the mandatory “stamp” on the glass cannot be found, it is possible to check the type of glass (float glass / fully tempered glass / heat strengthened glass) during inspection with a “Scattered Light Polariscope”. However, it is very hard to determine hidden damages in gluing or concealed problems in the constraint areas (e.g. in the area of point fixings).

Shelling defects are often hidden behind the clamping profiles (Figure 1) and may require a partial dismantling of the structure.

Figure 1. Shelling on a glass edge.

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Figure 2. Example for analysis of a bracket of an element façade

Figure 3. Typical detail with a missing screw and near edge mounting

Figure 4. Damaged box after impact of façade element Glass support

Structural Analysis There are significant problems regarding missing or incorrect structural analysis of glass and façade systems. As in the case of structural components of a building, a structural analysis is also necessary for a facade. This is often very complex and sophisticated. For example, finite-element analysis of the glass pane must cover all areas with stress peaks. Complexities also arise analysing the area of the bore in point-fixed glass panes. Façade elements are every expanding in size, transparency and filigree.

Construction of these delicate and intricate mountings are often ‘borderline’- and thus require stringent analysis before their adoption into a building design and construction. Miscalculation in structural analysis is one of several reasons that subject a façade to a high risk of damage and/or failure.

hidden screws are forgotten (Figure 3) or the wrong type is used where the distance to the edges is too small, ultimately resulting in the failure to fulfil their principal function as either an “anchor” or “expansion” point. An examination of screws often means dismantling the elements. Figure 4 shows a damaged box after the impact of a façade element fixed with incorrect screws.

Regarding glass support, rules concerning design and arrangement already exist. For example, the distance from the glass support to the edges should be a standard length. Moreover, the glass support must reinforce the full thickness of the glass pane. However, in reality, these rules are subject to external effects that complicate the fruition of them in practice (see Figure 5).

Screws Drilling screws and self-tapping screws are great products that can be used in the fixing of façade-elements.

However, these must also be subjected to rigorous structural analysis and design. It is not uncommon that

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Longitudinal expansion The length of thermal expansion of a façade must be considered in design. One solution is to design the connection to the substructure with fixed-points and moving points. In actual practice the moving points often do not exist, are either seized or flush with the end-stop.

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Figure 5. Too short glass support Leakage Leaking facades are a major point of concern, especially in attics or buildings with flat sloping roofs. In these cases, channels under the cover strips are often filled with silicone (Figure 6), which is detrimental. The moisture cannot run or dry off, resulting in standing water that shreds the edge seal, penetrating the cavity between the panes or sometimes into the rooms below.

Impact In addition to the structural analysis of glass, proof of impact is also necessary in the design and construction of facades. The requisite anti-drop device can then be utilized to secure the façade and elements. Frequently, glass thickness is specified according to past experience values or through calculations. In addition, a third method of laboratory testing or direct on-site testing can be used.

The standard testing method is the pendulum impact test which is used to determine the impact resistance, strength and breakage characteristics to ensure that the glass is fit for its intended purpose (see Figure 7). It is possible to configure and perform the test within an existing construction during inspection – however this is subject to the risk of glass breakage.

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Figure 6. Chanel filled with silicone

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD Research project: Development of a Mobile Device for the Evaluation of the Current in Situ Stress Condition in Glass Together with TU Ilmenau, RWTH Aachen and Verrotec GmbH Mainz, the consulting engineer’s office of the author is currently working on a research project. This project is funded by the German Federal Ministry of Economics and Energy (ZF4075115AG6) within the framework of the Central Innovation Program “Mittelstand” (ZIM) and deals with the development of a mobile device for the the evaluation of the current in situ stress condition in glass.

The primary aim is to produce a mobile device that can analyse facades that are already mechanically fixed and/or glued. A concept and functional model for the application of a mobile device for measuring qualitative flat stresses in glass components based on photoelasticity including application software is currently being developed. (Schaaf 2018). Photoelasticity is based on the visualization of the birefringence of optically isotropic or polarized light in transparent materials like glass with the aid of a circular polariscope. Unloaded glass is not subject to birefringent, but loaded glass exhibits the properties of birefringence due to the stress state in the glass. The polarized load vector splits into two perpendicular components when passing the loaded glass element (Figure 8).

The directions of this vectors are the same with regard to the principle stresses σ1 and σ2. The aptly named “main equation of photoelasticity” is shown in eqn (1) (Schaaf 2018, Hildebrand 2010)

C: photoelastic constant, σ1 and σ2: principle stress, λ: wavelength, δ: phase shift, D: thickness

Figure 7. Pendulum impact test

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In the Context of the research project, several experimental setups are being investigated. One of them with a bonding is shown in Figure 10. Within the scope of the investigations, both homogeneous bonds and faulty bonds were examined. The glass is loaded with 2000N. The higher the load, the brighter the areas around the adhesive (Figure 11). With the method of stress optics, the state of stress in the glass of bonded joints can be examined.

Refurbishment of facades Refurbishment of facades is often caused by progressions in technology and available products. For example the move away from monolithic layers to triple IGU’s or due to improvements in architectural aspects of design. The function of facades has changed in recent years. In high rise buildings, the façade is the main point of refurbishment.

Double Skin facades help to safeguard the well-being of users and improve the CO2-balance by providing cooling and air conditioning systems. There are a number of variations in design and functions that double skin facades serve.

The two layers of the façade serve two main purposes: While the outer layer protects users from external conditions like the weather, the inner layer functions as an insulation element (typically using insulation glass).

The outer layer is often static and unopenable, usually constructed using monolithic glass. The gap between the inner and outer layer is ventilated, with few openings in the outer façade to ensure sufficient ventilation. It is usually possible to open the inner layer, for the user to regulate the climatic surroundings inside the building. In the gap between the layers an exterior sun protection can be installed to safeguard against the weather and wind.

The strengthening of a facade may be necessary caused by: • Problems with the ultimate limit state caused by mistakes in design • Mistakes in execution • Problems with ultimate limit state caused by energetic renovation with thicker, heavier IGU’s

Figure 8. Schematic setup of circular polariscope (Schaaf 2017)

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD Possible Solutions include: • Strengthening of metal construction • Use of special glass products (e.g. stiff interlayers) to reduce the weight of glass • Complete new façades that adopt new technologies

Conclusions Façade construction is getting more and more complex. In addition to more stringent structural design, the inspection and monitoring of the structural integrity of a façade after several years is very important. New measurement methods based on photoelasticity may help to find hidden problems and serves as a positive progression in the field of façade safety. In addition, the refurbishment of facades may be necessary due to damage or in leu of advancements in technology, engineering knowledge and available products.

References (1) VDI Richtlinie 6200, Structural safety of buildings – Regular inspections, 2010.

(2) Siebert B., Maniatis I. A new Façade Concept for an Existing Office building. Challenging Glass 2 Delft 2010.

Figure 9. Experimental (a), simulated phase image (b), stress plot of a FE simulation (c) (Deuschle 2005)

(3) Siebert B. Modern Facades made of Glass. IABSE Chicago 2008.

(4) Siebert B. Modern Facades of tall building. GPD Tampere 2009.

(5) Siebert B. Refurbishment of facades. GlassCon Global 2018 Chicago (6) DIN 18008-1: 2010-12: Glas im Bauwesen – Bemessungsund Konstruktionsregeln – Teil 1: Begriffe und allgemeine Grundlagen.

(7) DIN 18008-2: 2010-12: Glas im Bauwesen – Bemessungsund Konstruktionsregeln – Teil 2: Linienförmig gelagerte Verglasungen.

(8) DIN 18008-2: 2011-04: Glas im Bauwesen - Bemessungsund Konstruktionsregeln - Teil 2: Linienförmig gelagerte Verglasungen, Berichtigung zu DIN 18008-2: 2010-12.

(9) DIN 18008-3: 2013-07:Glas im Bauwesen – Bemessungsund Konstruktionsregeln – Teil 3: Punktförmig gelagerte Verglasungen.

(10) DIN 18008-4: 2013-07:Glas im Bauwesen – Bemessungsund Konstruktionsregeln – Teil 4: Zusatzanforderungen an absturzsichernde Verglasungen.

Figure 10. Test specimen

(11) DIN 18008-5: 2013-07:Glas im Bauwesen – Bemessungsund Konstruktionsregeln – Teil 5: Zusatzanforderungen an begehbare Verglasungen.

(12) SIEBERT B., HERRMANN T., „Energetische Sanierung Hypo Hochhaus – Gebogene 3-fach Isolierverglasung der neuen Doppelfassade“ , Glasbau 2014, Ernst und Sohn Verlag Berlin, 2014.

(13) Schaaf, B., Abeln, B., Richter, C., Feldmann, M., Glaser, M., Hildebrand, J., Bergmann, J.-P. Development of a Mobile Device for the Evaluation of the Current in Situ Stress Condition in Glass. Challenging Glass Delft, Netherland 2018.

(14) Deuschle, H.M., Wittel, F.K., Kröplin, B.-H.: Simulation von Spannungsoptik im Rahmen der FEM, 17. Deutschsprachige ABAQUS Benutzerkonferenz, Nürnberg (2005)

Figure 11. Experimental phase image and 3-D plot of phase shift

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(15) Schaaf, B., Di Biase, P.,Feldmann, M., Schuler, C., Dix, S. Fullsurface and non-destructive quality control and evaluation by using photoelastic methods, Glass Performance Days 2017, Proceedings, Tampere, Finland, (2017)

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Glass Coatings Useful for the Prevention of Bird Collisions E. A. Axtell, III, J. Walker, G. Sakoske, A. Urmann, J. Henrish, D. Stotka and E. Porat Ferro Corporation, 7500 East Pleasant Valley RD, Independence, OH 44131, USA Abstract It is estimated that 100 million to 1 billion birds a year perish due to collisions with glass.1-2 In North America, some communities have enacted legislation aimed at protecting birds by calling for the design and installation of bird-safe glazing. Such glazing can be produced by printing human-visible, first-surface coatings on glass, in specific patterns. Another option is to print a UV-reflective coating on the glass to make use of the unique vision characteristics of birds. Such coatings have a lower visual impact on the human viewer. Candidate coatings have been tested at the Powdermill Avian Research Center in Rector, Pennsylvania, USA. Avoidance scores of 70 to 92% have been observed for the candidate coatings. The testing conditions and a description of the avoidance score will be discussed.

Introduction The transparency, strength and formability of glass makes it a material of choice for the exterior surfaces of buildings. The ability to make vacuum insulated glass (VIG) units, to decorate with enamels and functionalize the surfaces of the glass with reflective and electrochromic coatings further cements glass as a material for the future. While glass can be used to create awe-inspiring exterior surfaces for buildings, its use comes at a price. It is estimated that by the American Bird Conservancy that 100 million to 1 billion birds a year are killed by collisions with glass. Here, permanent glass coatings useful for the prevention of bird strikes will be discussed.

Materials Annealed soda-lime glass sheets with a thickness of 3.5 to 4 mm were cut to 1 meter by 0.5 meters and the edges of the panes were seamed. The glass was then washed in an industrial washer, dried and stacked for use. First surface enamels in four colors were obtained from Ferro Corporation of Washington, PA, USA. The colors of Blue, Green, Sweatshirt Gray and Etch were chosen due to the demand for these colors in architecture. TC1557-31B Paste and TC1557-31N Paste were obtained from the Ferro Corporation Technical Center of Independence, OH, USA. Nylon screens with a mesh sizes 110.80 and 305.40 (each denoting mesh/inch and thread size in microns, respectively) were obtained from Schilling Graphics of Galion, OH, USA. Tempering line time was obtained from Paragon Tempered Glass of Antwerp, OH, USA and Laurier Glass of Quebec City, QC, Canada. Digital printing and tempering of a 1 meter x 0.5 meter pane was arranged by DipTech, A Ferro Company of

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Smithfield, RI, USA. Wild song birds were netted at the Powdermill Avian Research Center in Rector, PA, USA. UV-Vis-NIR spectra were obtained on a Perkin-Elmer Lambda 950 UV-Vis-NIR Spectrophotometer and a Perkin-Elmer Lambda 1050 UV-VisNIR Spectrophotometer. UV Photography was accomplished using a UV-SYS-01, available from Oculus Photonics of Santa Barbara, CA, USA. Experimental First Surface Enamels. The first surface enamels obtained from Ferro Corporation in Washington, PA were printed onto the soda-lime glass panes with 110.80 Mesh nylon screens. One screen possessed vertical stripes with a width of 1” (2.5 cm), which were spaced apart by 2” (5 cm). This screen was used to print the Etch enamel only. Another screen possessed a diagonal array of ½” (12.5 mm) dots, with their centers spaced 2” (5 cm) apart. This second screen was used to print all four colors.

After printing, the panes were passed through a drying oven to remove the screen print solvent from the prints. The glass was then tempered, using a furnace temperature of 710°C and push rates and quenching parameters usual for the 4 mm glass upon which the prints were made. After cooling, the panes were packaged for shipping.

Digital-Ceramic-Printed Pane. A pattern of random triangles of different colors was designed by Dr. C. Shepperd of the American Bird Conservancy and was submitted to Dip-Tech, A Ferro Company for digital ceramic printing. A 1 meter x 0.5 meter pane of glass was printed with the pattern and tempered in a similar manner to what was described above.

Multi-Layer Coatings. An automatic screen printer was set up with a 305.40 Mesh screen in the stripe pattern. TC1557-31B Paste was then applied to the screen for printing. Prints were made and the glass was passed through a drying oven and fired with a tempering fire. This print deposits a relatively high indexof-refraction oxide coating on the glass after firing. The excess paste was removed from the screen and it was washed with de-natured alcohol. After the screen was dry, it was set up with TC1557-31N Paste. The previously fired panes were then printed a second time. The paste was applied to the glass over the previously fired layer. The glass was again placed in a drying oven to remove the solvent from the print. The pane was then sent through a tempering fire a second time. The TC1557-31N

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD Paste fires to provide an oxide layer with a relatively low index of refraction. To complete the three-layer coating, the screen was set up with the TC1557-31B Paste again and panes with two fired layers already applied were printed a third time. In a similar manner, the five-layer coating was completed by adding print/dry/fire cycles for the TC1557-31N Paste and the TC155731B Paste to panes already printed with three layers. The glass was packaged to ship.

Flight Tunnel Testing. The flight tunnel test has been described in detail elsewhere.3-4 In summary, wild song birds are netted at the Powdermill Avian Research Center. The birds are examined for species, sex and health before being banded. If the bird appears to be “bright,” meaning that it was not too stressed from the capture and banding process, it is placed in a dark cloth bag. Meanwhile, the flight tunnel is set up. The apparatus consists of rectangular structure with approximate inside dimensions of 1 meter by 1.5 meter by 10 meter. The interior of the structure is lined with black felt. On one side, mirrors are used to cast light on a blue and white, cloud and sky scene, which is spaced away from the end of the tunnel. Two panes of glass are mounted at the end of the tunnel. One pane is a blank of untreated glass. The other pane is the treated pane. Inside the tunnel, near the glass, a thin safety net is located. This net prevents birds from actually contacting the glass during testing. The tunnel can be rotated to catch the sun in the best manner. At the opposite end of the tunnel from the installed glass, a small port allows for the bird, contained in the felt bag, to be inserted into the tunnel and released. The bird choses a pane of glass at which to fly, bounces off the safety net and is then free to go through as small opening to the side of the safety net. The flights are videotaped so that investigators can determine at which pane the bird flies. The goal is for the bird to see the coated glass and to choose to fly at the blank glass every time. The statistics generated result in the formulation of an avoidance index or AI. An AI near 50% indicates random behavior, where the coating does not give the bird any queue. The American Bird Conservancy gives a rating of “Preferred” to any coating that gives an AI of 70% and a rating of Most Preferred to any coating that achieves an AI of 80% or more.

Optical Characterization. UV-Vis-NIR spectra were obtained on a Perkin-Elmer Lambda 950 and a Perkin-Elmer Lambda 1050. Both instruments were equipped with a Spectralon-lined integrating sphere, which allows data collection from 250 nm to 2500 nm. Both % Transmission and % Reflectance spectra were obtained. % Reflectance are of more importance to this discussion. The substrate glass usually reflects about 5% of the UV light. Since it is known that birds need a contrast of 20% or to see and avoid the glass, engineering coatings with good reflectance values allows for the best chance to create a useful coating.

UV Images. UV images were obtained with a camera obtained from Oculus Photonics. The camera was equipped with a band-

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Figure 1. (Upper Left) A UV Image of an imitation etch first surface coating, printed in a stripe pattern and illuminated with conventional fluorescent light. (Upper Right) A conventional, interior photograph of the etch-printed glass. (Lower Left) UV Image of the etch-printed glass illuminated with 395 nm light. (Lower Right) A conventional, exterior photograph of the etch-printed glass.

Figure 2. (Upper Left) A UV Image of a green first surface coating, printed in a dot pattern and illuminated with conventional fluorescent light. (Upper Right) A conventional, interior photograph of the green-printed glass. (Lower Left) UV Image of the greenprinted glass illuminated with 395 nm light. (Lower Right) A conventional, exterior photograph of the green-printed glass.

Figure 3. (Upper Left) A UV Image of a blue first surface coating, printed in a dot pattern and illuminated with conventional fluorescent light. (Upper Right) A conventional, interior photograph of the blue-printed glass. (Lower Left) UV Image of the blue-printed glass illuminated with 395 nm light. (Lower Right) A conventional, exterior photograph of the blue-printed glass.

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD pass filter with a transmission band from 335 nm to 510 nm.

This range was chosen in an attempt mimic the wavelengths visible to bird through two of their four cones. The detector of the camera therefore measures the amount of reflected or emitted light in the range of 335 to 510 nm from the object, theoretically giving humans an idea of what a bird would be capable of seeing. Illuminators at wavelengths of 365 nm and 395 nm were used to light the panes. The panes were set up against a black background for UV photographs.

Discussion Several strategies exist for reducing bird collisions with glass, according to “Bird-Friendly Building Design,” published by the American Bird Conservancy. A major initiative is to request that the lights be turned off in high-rise buildings at night. Other, semi-permanent strategies are also possible. Parachute cord can be hung in front of windows to make Acopian Blinds. Stickers or tape can also be applied to glass to help the birds to see and avoid it. These strategies suffer because they are not permanent, weather-durable solutions. Permanent, weatherdurable options exist. The glass can be acid-etched in birdfriendly patterns to give glass with some utility for reducing strikes. A detriment to this technique is that the color is basically restricted to variants of the etch appearance. Another option is to laminate a plastic sheet containing UV-absorbing material printed in a bird-friendly pattern between two panes of glass. This strategy was examined in reference 1. The goal of the present work is to supply permanent, bird-friendly coatings for glass that can possess vivid colors or be nearly transparent to humans.

Based on discussions with ornithologists Dr. Christine Sheppard of the American Bird Conservancy and Prof. Daniel Klem, Jr. of Muhlenberg College, Dept. of Biology, bold patterns of stripes and dots were designed for the testing of the first surface enamels and multi-layer coatings. The goal of the research was to prove that the materials printed on the glass are suitable for the prevention of bird strikes and not what patterns are useful. The dimensions of the features of these coatings

Table 1. Flight Tunnel Test Results.

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were chosen based on the results described references 5-11. Basically, this is the 2” x 4” (5 cm x 10 cm) rule. Horizontal lines or rows of dots should be placed 2 inches (5 cm) apart and vertical lines or rows of dots should be spaced 4 inches (10 cm) apart.

Such dimensions give the bird the impression that it cannot fit between the markings and thus it should divert from the approaching barrier. If the goal is to prevent hummingbird strikes, it has been found useful to reduce the spacing of the vertical features to 2 inches (5 cm) as well.

The first aim in this work was the design of the transparent, multi-layer coatings seen in Figure 6 and the last two entries of Table 1. The goal was to make use of the fourth type of cone that birds possess in their eyes compared to humans, please see Figure 7. It should theoretically be possible to manufacture coatings that are UV reflective, with a peak at 370 nm, that are also nearly invisible to human beings. So called ¼ Wave Stacks were chosen as a strategy for producing these coatings. Two pastes were designed, one with a relatively high index of refraction and the second with a relatively low index of refraction.

When the pastes are printed with the correct film depth and fired, they give oxide layers with thicknesses on the scale of ¼ of the wavelength of the light that is desired to be reflected, here meaning 50 to 80 nm thick. When the coatings were submitted for tunnel testing, it was found that birds can in fact see the coatings and divert from them, as noted by the avoidance indices of 80% and 71%, respectively, for the three-layer and five-layer coatings.

In order to visualize the coating as a bird could, a camera optimized to collect UV light was procured. Filters for the camera were chosen so that light with wavelengths of 350 to 510 nm were allowed to strike the detector. This is the closest mimic possible the UV and violet-centered cones that birds possess, as seen in Figure 7. The UV images in fact show good reflection of the UV light, especially for the image taken with 395 nm illumination, please see Figure 6, Upper Left and Lower Left.

Due to the physics of the oxide layers applied during the manufacture of the coatings, there is some human-visible component to the multi-layer coatings. In the interior view of Figure 6 Upper Right, an orange color exists when the coating is viewed from the inside. Upon viewing the coating from the outside, a mirror-like appearance is seen, please see Figure 6 Lower Right. It is possible that the visual impact of this coating could be minimized by reducing the size of the printed features. Another problem with these multi-layer coatings is the intensive processing needed to manufacture them. Three to five cycles of printing, drying and firing are needed to apply the coatings. Glass fabricators are also loath to firing the glass multiple times, fearing that there could be breakage issues during the second and higher firing cycles.

With these concerns in mind, the strategy next turned to submitting first surface coatings to tunnel testing. These coatings are designed to be applied to the exposed surface of the glass.

The coatings therefore need to be weather durable and should not cause undue stress related weakness to the substrate glass. The imitation Etch coating was printed in two different

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD patterns, a broad stripe pattern and in a dot pattern. The Etch enamel is shown printed in the stripe pattern in Figure 1. In addition, three other colors of architectural interest were chosen for the study: Green, Blue and Sweatshirt Gray, as seen in Figures 2-4. As can be seen in Table 1, all of the coatings show significant activity toward diverting birds from strikes, due to the avoidance indices in the range of 76 to 87%. The Etch print in the stripe pattern attained a rating of “Preferred” by the American Bird Conservancy, since it possesses an AI>70%. The four trials printed in the dot pattern attained the “Most Preferred” rating from the American Bird Conservancy due to AI’s>80%.

The highest score for the first surface coatings was attained by the Green coating. Possibly, the good contrast it has from blue sky and clouds is responsible for this behavior.

A digitally printed sample was also submitted for testing at the flight tunnel, please see Figure 5 and Table 1. This print gave the best performance of all of the trials, with an AI of 92%.

It is interesting to consider the reasons why this coating performs so well. The outdoor image of the coating shows that there is good color contrast between the coating and the blue sky and clouds reflected from the glass, even to humans. The coating also shows various shades of gray in the UV images, so it is possible that all four types of cones in the birds’ eyes are seeing contrast. The pattern shapes are also “unnatural.” The triangles do not resemble trees, animals, rocks or even buildings. This could be a powerful queue to the birds to divert form the glass.

Conclusions It is possible to provide permanent coatings for glass that can help birds to see the glass and avoid it. This conclusion is based on the results of flight tunnel testing of various coatings at the Powdermill Avian Research Center in Rector, PA, USA, which is under the direction of the Carnegie Museum of Natural History in Pittsburgh, PA, USA. The Avoidance Indices (AI’s) of 71 to 92% indicate that 71 to 92% of birds chose to fly at the blank glass set up beside the test pane because they can see the pattern on test pane. These behaviors allow the American Bird Conservancy to give ratings of “Preferred” for coatings with AI>70% and “Most Preferred” for coatings with AI>80%.

The optical reasons such coatings work well were examined with the use of a UV Camera, a conventional camera and a UVVisible-NIR spectrometer. Coatings such as the 3-Layer and 5-Layer Coatings with relatively low visible impact to humans can be quite visible to birds. This can be seen by examining the large peaks in the % Reflectance (%R) spectra of Figure 7 and comparing them to the UV Camera images and the humanvisible images seen in Figure 6. Human-visible colors also work to deter bird strikes. The variable colors of the digitally printed triangles gave the best results with an AI of 92%.

Future Work The work of preventing bird strikes has just barely begun. It is necessary to begin building an approved list of patterns and colors that prevent bird strikes. The use of digital printing will

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Figure 4. (Upper Left) A UV Image of a gray first surface coating, printed in a dot pattern and illuminated with conventional fluorescent light. (Upper Right) A conventional, interior photograph of the gray-printed glass. (Lower Left) UV Image of the gray-printed glass illuminated with 395 nm light. (Lower Right) A conventional, exterior photograph of the gray-printed glass.

Figure 5. (Upper Left) A UV Image of the digitally printed coating, printed in a randomly colored triangle pattern and illuminated with conventional fluorescent light. (Upper Right) A conventional, interior photograph of the digitally-printed glass. (Lower Left) UV Image of the digitally-printed glass illuminated with 395 nm light. (Lower Right) A conventional, exterior photograph of the digitally-printed glass.

Figure 6. (Upper Left) A UV Image of a 5-Layer Coating, printed in a stripe pattern and illuminated with 365 nm light. (Upper Right) A conventional, interior photograph of the 5-Layer Coating. (Lower Left) UV Image of the 5-Layer Coating illuminated with 395 nm light.

(Lower Right) A conventional, exterior photograph of the 5-Layer Coating.

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GPD FINLAND 2019 – SHARING KNOWLEDGE AROUND THE WORLD be of great assistance in this endeavor, since both the patterns and the colors can be infinitely varied. At a certain point, it should be theoretically possible to certify a material for bird safe glazing if it is printed in a “bird friendly pattern,” so that the testing costs will be reduced. Work should be undertaken to expand the color palate for first surface coatings, giving architects and clients a wider array of colors and appearances from which to choose.

The flight tunnel test is an interesting and reproducible method for obtaining data on what birds can and cannot see during flight and currently is the method by which coatings are certified. However, a second method exists that may be more realistic. Klem and co-workers at Muhlenberg College in Allentown, PA, USA have developed a competing method. A bird feeder is set up in the middle of a meadow surrounded by forest. At the edges of the clearing, frames are set up for the 3’ x 4’ (approximately 1 meter x 1.3 meter) test panes. The frames are set so that the birds can fly above, below or to the sides of the pane. Two panes of each pattern are needed for the test. One pane is placed in a frame with no backing, to mimic a window in a greenhouse or breezeway. One pane is set in a frame and

is backed by a black curtain to mimic a window in a dark house.

Each day, the panes are monitored early in the morning and in the evening to determine the number of strikes and specimens that occur for each pane. This test goes on for six months and so is quite labor intensive and expensive. But a coating that could pass both types of testing should be considered as stateof-the-art.

Acknowledgements This work would not have been possible without a lot of assistance and previous research. Groups such as Chicago Bird Collision Monitors, FLAP Canada and BirdSafe Pittsburgh, to name just a few, monitor buildings for dead and injured birds. It is the statistics that these groups generate that have brought this issue to light. Dr. Christine Sheppard is thanked for her support, training and her design of the randomly colored, triangle pattern that scored so well in flight tunnel testing. Prof. Daniel Klem, Jr. is thanked for interesting discussions during a pleasant dinner in Allentown, PA. The glass cutting, press room, drying line and tempering line crews at Paragon Tempered Glass of Antwerp, OH, USA and Laurier Glass of Quebec City, QC, Canada are thanked for the glass fabrication of the first surface and multi-layer trials used in this work, respectively. Dip-Tech, A Ferro Company, is thanked for arranging for the digital printing and tempering of the multi-colored triangle pattern designed

by Dr. Sheppard. The technicians and scientists at the Powdermill Avian Research Center in Rector, PA, USA are thanked for the testing that they conducted on the glass trials.

References 1. “Evaluating the Effectiveness of Select Visual Signals to Prevent Bird-Window Collisions.” D. Klem, Jr. and P. G. Saenger. The Wilson Journal of Ornithology, 125(2): 406-411, 2013.

2. “Bird-Building Collisions in the United States: Estimates of Annual Mortality and Species Vulnerability.” S. R. Loss, T. Will, S. S. Loss, and P. P. Marra. The Condor, Vol. 116, 8-23, 2014.

Figure 7. UV-Vis-NIR Spectroscopy of the blank glass, the 3-Layer Coating and the 5-Layer Coating.

3. “Farben-Glasdekorfolie-Getöntes Plexiglas 12 Weitere Experimente im Flugtunnel II.” M. Rössler and W. Laube. Vermeidung von Vogelanprall am Glasflächen, 1-36, 2008.

4. “Glass Pane Markings to Prevent Bird-Window Collisions: Less Can Be More.” M. Rössler, E. Nemeth and A. Bruckner. Biologia, Vol. 70/4, 535-541, 2015.

5. US Patent 8,114,488 B2. “Window for Preventing Bird Collisions.” J. Alvarez. Feb. 14, 2012.

6. US Patent 8,114,503 B2. “Method and Apparatus for Preventing Birds from Colliding with or Striking Flat Clear and Tinted Glass and Plastic Surfaces.” D. Klem, Jr. Feb. 14, 2012.

7. US Patent 8,389,077 B2. “Window for Preventing Bird Collisions.”

J. Alvarez. Mar. 5, 2013.

8. US Patent 8,506,089 B2. “Avian Deterrent for Glass Using Projected UV Light.” K. W. Kayser. Aug. 13, 2013.

9. US Patent 8,869,480 B2. “Method and Apparatus for Preventing Birds from Colliding with or Striking Flat Clear and Tinted Glass and Plastic Surfaces.” D. Klem, Jr. Oct. 28, 2014.

Figure 8. Human Vision versus Avian Vision, as seen in “BirdFriendly Building Design,” published by the American Bird Conservancy.

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10. US Patent 9,650,290 B2. “IG Window Unit for Preventing Bird Collisions.” G. Vikor and B. Disteldorf. May 16, 2017.

11. US Patent 9,862,835 B2. “Window Coating.” P. Thottathill, P. Kesavan, J. Ryan and S. Mukherjee. Jan. 9, 2018.

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