Construction and architecture of high rise buildings and skyscrapers

Elvijs Josts 30.09.2016

SEPTEMBER 30, 2 016

CONSTRUCTION AND ARCHITECTURE OF HIGH-RISE BUILDINGS AND SKYSCRAPERS BACHELOR DISSERTATION

ELVIJS JOSTS VIA UNIVERSITY COLLEGE CAMPUS HORSENS

Elvijs Josts 30.09.2016

TITLE PAGE Architectural Technology and Construction Management BATCoM

TITLE of DISSERTATION: Construction and architecture of high-rise buildings and skyscrapers

CONSULTANT: Erik Toft AUTHOR: Elvijs Josts

Student number: 144070 Date: 30.09.2016 Number of copies: 1 Number of pages: Dissertation only: 31 (2400 characters per page) All: 37 pages Number of characters: Dissertation only: 61 642 All: 68 248 Font: Calibri 12

All rights reserved – no part of this publication may be reproduced without the prior permission of the author.

NOTE: This dissertation was completed as part of a Bachelor of Architectural Technology and Construction Management degree course – no responsibility is taken for any advice, instruction or conclusion given within.

Elvijs Josts 30.09.2016

Preface This is a final dissertation for Architectural Technology and Construction Management Bachelor degree in VIA University College Campus Horsens with an elective subject on highrise buildings and skyscrapers.

This report has been written on my research of tall buildings and skyscrapers in literature, dissertations, articles and books. Illustrations and figures used in this dissertation are taken from different sources on the internet. The list of bibliography used in writing this dissertation can be found at the very end of the report.

Acknowledgements Firstly, I would like to thank VIA University and all my teachers who helped me to get through this education by expanding my knowledge and interest in this constructing architecture field.

Also I would like to thank my dissertations supervisor Erik Toft, for being patient and helpful towards me and I am thankful for all the advices he gave me to make this dissertation what it is.

Secondly, I would like to give special thanks to Gabija Kaltenyte, for giving me some good advices and helping me to improve myself and this paper. Also thanking all my colleagues and friends in VIA University College and BIM Training Studio.

Also I cannot thank enough my father and mother for always believing in me, supporting me and encouraging me to get where I am now.

Abstract This dissertation tries to explain how we have developed in building tall buildings and structures and why should we build such buildings.

The paper starts with a history of tall structures, dated back B.C. and how we got till where we are now, regarding tall buildings, by giving some examples of tallest buildings today and their specifications. Next this report goes into history of development of structural systems for tall buildings and explains all structural systems being used nowadays. It continues with reasons and arguments why we should be building and developing such structures, and advantages and disadvantages of them. This paper also will look into future of tall buildings and envisioned structures which most likely will not get constructed any time soon.

In the end this paper I will answer and conclude all my research on the chosen topic.

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Key words High-rise buildings, skyscrapers, tower blocks, history, pyramids, world wonders, wooden high-rise buildings, tall buildings, sustainability, structural systems,

List of Illustrations Image 1. Great Pyramid of Giza. ................................................................................................. 8 Image 2. Temple of Neptune in Rome........................................................................................ 9 Image 3. 3D model of Byzantine Ziggurat. ............................................................................... 10 Image 4. El Castillo – Temple of Kulkan. ................................................................................... 11 Image 5. The Flaxmill, Ditherington, England........................................................................... 12 Image 6. Burj Khalifa in Dubai .................................................................................................. 14 Image 7. Shanghai tower in China ............................................................................................ 15 Image 8. Radio and TV tower in Riga ........................................................................................ 16 Image 9. Z Towers in Riga, Latvia. ............................................................................................ 17 Image 10. Exterior structure ..................................................................................................... 19 Image 11. Interior structure ..................................................................................................... 19 Image 12. Tuned mass damper in Taipei 101 in Taipei, Taiwan .............................................. 28 Image 13. Jeddah Tower in Jeddah, Saudi Arabia ................................................................... 32 Image 14. Tallest buildings ever proposed. .............................................................................. 33

List of Figures Figure 1. Countries Ranked by Total Number of Completed Buildings .................................... 13 Figure 2. Tallest completed buildings ....................................................................................... 13 Figure 3. Interior structures...................................................................................................... 19 Figure 4. Exterior structures ..................................................................................................... 22

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Elvijs Josts 30.09.2016

Contents Preface ........................................................................................................................................ 2 Acknowledgements .................................................................................................................... 2 Abstract ...................................................................................................................................... 2 Key words ................................................................................................................................... 3 List of Illustrations ...................................................................................................................... 3 List of Figures .............................................................................................................................. 3 1. Introduction ........................................................................................................................ 5 1.1. Background information .............................................................................................. 5 1.2. Professional relevance and aims ................................................................................. 6 1.3. Problem formulation ................................................................................................... 6 1.4. Delimitation ................................................................................................................. 6 1.5. Theoretical basis and sources of empirical data ......................................................... 6 1.6. Choice of methodology and empirical data................................................................. 7 1.7. Overall structure and rationalization of the dissertation ............................................ 7 2. History and tall buildings now ............................................................................................ 8 2.1. History of tall buildings ................................................................................................ 8 2.2. Tallest buildings now ................................................................................................. 12 2.2.1. Burj Khalifa.......................................................................................................... 13 2.2.2. Shanghai tower ................................................................................................... 14 2.3. Tall buildings in Latvia ................................................................................................ 15 3. Construction and design ................................................................................................... 17 3.1. Development of structural systems ........................................................................... 17 3.2. Design of tall buildings ............................................................................................... 18 3.3. Structural systems of tall buildings ............................................................................ 18 3.4. Issues and concerns in tall buildings .......................................................................... 25 4. Reasoning behind tall buildings and skyscrapers ............................................................. 29 4.1. Advantages and disadvantages of tall buildings ........................................................ 30 5. Sustainability in tall buildings ........................................................................................... 30 6. Future of tall buildings ...................................................................................................... 32 6.1. Under construction .................................................................................................... 32 6.2. Envisioned tall buildings ............................................................................................ 33 7. Conclusion ........................................................................................................................ 34 Bibliography .............................................................................................................................. 36

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1. Introduction This dissertation is written as a compulsory 7th semester dissertation in Architectural Technology and Construction Management program at VIA University College Campus Horsens in Denmark, and covers history of high-rise buildings, construction and materials used in building them, sustainability and future of tall buildings.

Throughout my studies I have not worked with high-rise buildings or skyscrapers, so I decided to write my dissertation about this topic as I find it very interesting, also more and more cities build tall buildings because of their development as economic center, increase of people and need for accommodation and workplaces. I will not try to come up with a new or innovative construction methods regarding high-rise buildings, I will research and analyze history and construction of such buildings, and include sustainable solutions.

1.1.

Background information

A tower block, high-rise, apartment tower, residential tower, apartment block, block of flats, or office tower is a tall building or structure used as a residential and/or office building. In some areas it may be referred to as an "MDU", standing for "Multi Dwelling Unit". A skyscraper is a tall, continuously habitable building of over 40 stories, mostly designed for office, commercial and residential uses. A skyscraper can also be called a high-rise, but the term skyscraper is often used for buildings higher than 150m. For buildings above a height of 300m, the term Supertall can be used, while skyscrapers reaching beyond 600m are classified as Megatall.

Different classifications of high-rise buildings: Emporis standards – “A multi-story structure between 35-100 meters tall, or a building of unknown height from 12-39 floors is termed as high rise.

Building code of Hyderabad, India – A high-rise building is one with four floors or more, or one 15 meters or more in height.

The International Conference on Fire Safety – "any structure where the height can have a serious impact on evacuation “ Massachusetts, United States General Laws – A high-rise is being higher than 70 feet (21 m).

Building such tall buildings is big engineering and architectural challenge, which pushes our limits and technology to improve. Such buildings are results of increasing demand of residential and business space and overall economic growth.

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1.2.

Professional relevance and aims

High-rise buildings and skyscrapers are becoming more and more popular. Cities are becoming overpopulated and there is bigger need for accommodation and workplaces. A high-rise building helps to save so valuable space and yet helps the city to expand vertically. Also the endless competition to build the tallest building, pushes technology, materials and constructions to develop and improve. In my opinion, as a construction architect, I find skyscrapers and high-rise buildings very relevant to all building industry. Even though skyscrapers are not so popular in Europe, which is slowly changing, development of these constructions influence and helps architectural technology all over the world.

1.3.

Problem formulation

I am writing this dissertation as a research paper.

Main research question is: 

How have we and technology developed in building high rise buildings and skyscrapers?

Where I am going into depth and look at these secondary questions:     

History of tall buildings?

What are different construction and structural system types of tall buildings?

Issues and concerns in tall buildings / skyscrapers?

What sustainable solutions are being used in tall buildings?

What is the future of tall buildings?

Also I am going to look a little into Latvia’s tallest buildings, as this is my home country.

1.4.

Delimitation

This dissertation will not focus on one or few countries. I will not research costs of skyscrapers and high-rise buildings. Time of construction and management of construction and building sites will also not be part of my dissertation. I will not look at construction and types of foundation used in tall buildings.

1.5.

Theoretical basis and sources of empirical data

All the data used in writing this dissertation will be collected from literature found in library, journal articles, other specialist researches, interviews and websites. Most of the information will be based on Europe, although in some parts of dissertation I will go further and research topics worldwide.

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1.6.

Choice of methodology and empirical data

In this dissertation I will mostly focus on using secondary research and relevant data from literature (books and articles) and information found on internet. As well I will include my own observations. This dissertation will mostly contain qualitative data.

1.7.

Overall structure and rationalization of the dissertation

The dissertation is based on an overall 3-part structure, which includes: 1. Introduction with problem formulation 2. Main section containing analysis, argumentations and part conclusions.

3. Conclusion answering the questions defined in problem formulation.

In order to conclude this dissertation, I will use my knowledge as well as solutions and opinions found in literature and articles, but mostly in conclusion I will include my own views and opinions about this topic.

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2. History and tall buildings now In this section I will research and go through history of tall buildings. Also I will look into tallest buildings built at the moment.

2.1.

History of tall buildings

The tallest buildings on earth are being called Skyscrapers, but this term was only introduced in the late 19th century in United States of America, it was applied to buildings of steel framed construction taller than 10 stories. How these tall buildings were called before this? Pyramids, churches, towers and/or Seven World Wonders. Then, when these seven famous buildings stood in all their beauty, people traveled, walked and sailed just to see them, just like in nowadays, although now these “miracles” are hundreds and thousands all over the world.

In ancient times the tallest building was The Great Pyramid of Giza, which is 146 meters tall. It was not surpassed in height for 3,800 thousands of years and is still standing proudly in Egypt.

Back in these days, old Egypt – in Africa, Greece and Rome – in Europe, Byzantine – in Asia and old Aztec and Mayan cultures in America people were building surprisingly big and tall buildings. Mostly they were religious buildings, to impress and satisfy their leaders and gods and to show their superiority. As I mentioned before, in old Egypt they were pyramids.

Image 1. Great Pyramid of Giza.

Pyramids in Egypt are still surrounded by a lot of controversy, about how and who has built them and nevertheless they are still one of the most visited tourism objects in the world. They were constructed 2580–2560 BC. Probably with our technology and prefabrication we could replicate and built one of these wonders, but it would cost way too much and take way too much time as well as too much manpower. The Great Pyramid is constructed of an estimated 2.3 million blocks, there are few theories how they could have built such a construction at that period of time.

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Elvijs Josts 30.09.2016 In old Greece and Rome, they were temples.

Image 2. Temple of Neptune in Rome.

Greek temples are a rectangular building, and were almost always approximately twice as long as they were wide. There are also some surviving circular structure temples, which are being referred to as tholos. Construction of these temples consists of naos(cella) – chamber in the middle of temple surrounded by windowless walls, inside housing statue of the god. Naos is usually surrounded by massive columns. They were constructed between 700 BC and 200 BC. Examples:

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Distyle in antis describes a small temple with two columns at the front, which are set between the projecting walls of the pronaos or porch, like the Temple of Nemesis at Rhamnus. (Fletcher, 2001) Amphiprostyle tetrastyle describes a small temple that has columns at both ends which stand clear of the naos. Tetrastyle indicates that the columns are four in number, like those of the Temple on the Ilissus in Athens. (Fletcher, 2001) Peripteral hexastyle describes a temple with a single row of peripheral columns around the naos, with six columns across the front, like the Theseion in Athens. (Fletcher, 2001) Peripteral octastyle describes a temple with a single row of columns around the naos, with eight columns across the front, like the Parthenon, Athens. (Fletcher, 2001) Dipteral decastyle describes the huge temple of Apollo at Didyma, with the naos surrounded by a double row of columns, with ten columns across the entrance front. (Fletcher, 2001) The Temple of the Olympian Zeus, Agrigento, is termed Pseudo-periteral heptastyle, because its encircling colonnade has pseudo columns that are attached to the walls of 9

Elvijs Josts 30.09.2016 the naos. Heptastyle means that it has seven columns across the entrance front.

(Fletcher, 2001) In Byzantine – Ziggurat.

Image 3. 3D model of Byzantine Ziggurat.

Ziggurats are part of the temple complex which included other buildings. They were constructed between 3000 BC and 2000 BC. Ziggurats were a form of temple common to the Sumerians, Babylonians and Assyrians of ancient Mesopotamia. The earliest examples of the ziggurat date from the end of the third millennium BCE and the latest date from the 6th century BCE. Built in receding tiers upon a rectangular, oval, or square platform, the ziggurat was a pyramidal structure. Sun-baked bricks made up the core of the ziggurat with facings of fired bricks on the outside. The facings were often glazed in different colors and may have had astrological significance.

The number of tiers ranged from two to seven, with a shrine or temple at the summit. Access to the shrine was provided by a series of ramps on one side of the ziggurat or by a spiral ramp from base to summit.1

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http://www.crystalinks.com/ziggurat.html

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Elvijs Josts 30.09.2016 And in old American culture – Mesoamerican pyramids.

Image 4. El Castillo – Temple of Kulkan.

Mesoamerican pyramids are more similar to Ziggurats than to the Ancient pyramids of Egypt, they are step pyramids with temples on top. A lot of cultures were building these kind of pyramids. Mayans built them between 200 and 900 AD. Aztecs built them between 12 th and 16th century in order to house and honor their deities.

In Europe tall buildings were mostly churches for Christianity, which had tall towers.

Tall buildings were also build in Yemen in 16th century, five to nine stories high buildings, to have a protection from Bedouin attacks. In 17th century in Edinburgh, Scotland, they started to construct tall stone buildings, it is because the territory of the city was limited of its protection walls, but as the city was growing fast, they needed to expand vertically. These houses were usually 11 stories tall, some even 14 stories high.

In 1797 in Ditherington, England, the first iron-framed building in the world was born. It is seen as a world’s first skyscraper described as “the grandfather of skyscrapers”, despite only being as tall as five-story building nowadays. The construction of the mill ran from 1796 till 1798.

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Image 5. The Flaxmill, Ditherington, England.

In late 19th century tall building development was mostly based on economical point of view – building vertically, expanding office space and maximizing rent income. So new technologies were pursued, changing the conventional load-bearing masonry walls with relatively small openings to iron/steel frame, which minimized the size of building perimeters. Because of this new iron/steel frame the openings were quite larger and there was need to fill them up, these openings were filled up with transparent glass, while the iron/steel structure were clad with other materials such as brick or terra cotta (a type of earthenware, is a clay-based unglazed or glazed ceramic, where the fired body is porous). Because of this new steel structure, new cladding system was developed – curtain wall. Which is used specifically a lot in building skyscrapers. From this point on high rise buildings became quite popular and were built mostly in United States of America, mostly for office spaces. Also different structural systems were developed which opened new possibilities and new heights to reach. I will talk more about history of structural systems in Chapter 3.

2.2.

Tallest buildings now

In this subsection I will look at top 5 highest buildings built nowadays. In the list bellow you can see the top 5 ranked by total number of completed tall buildings (Counts on buildings under 150 m may be incomplete).

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Figure 1. Countries Ranked by Total Number of Completed Buildings2

Figure 2. Tallest completed buildings

There are also 2 other skyscrapers which are almost completed (topped out but not completed), it means its external structure is built, but building itself, interior is not finished.

Ping An Finance Centre, which will be 4th tallest building after its completion – 600 m in height, Lotte World Tower, which will take 5th tallest building after its completion – 555 m.

2.2.1. Burj Khalifa Burj Khalifa (formerly known Burj Dubai) is the tallest building in the world, its standing at 829.8 m to its tip and 828 m architectural height, it is made out of steel and concrete. Burj Khalifa has redefined what is possible in the design and engineering of supertall buildings. By combining cutting-edge technologies and cultural influences, the building serves as a global icon that is both a model for future urban centers and speaks to the global movement towards compact, livable urban areas.

This skyscraper was designed by Skidmore, Owings & Merrill LLP, it was proposed on 2003, and its construction started on 2004 and it was completed by year 2010 in Dubai.

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http://skyscrapercenter.com/countries?list=buildings

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Elvijs Josts 30.09.2016 Image 6. Burj Khalifa in Dubai

The exterior cladding was designed to withstand Dubai’s extreme temperatures during hot months of summer, it’s made of comprised of aluminum and textured stainless steel spandrel panels and using a Low-E glass for enhanced thermal insulation. They have added polished stainless steel fins, to accentuate buildings height and slenderness.

Burj Khalifa has one of the largest condensate recovery systems in the world. Collecting water from air conditioning condensate discharge prevents it from entering the wastewater stream and reduces the need for municipal potable water.

The structural system, termed a “buttressed core,” is designed to efficiently support a supertall building utilizing a strong central core, buttressed by its three wings. The vertical structure is tied together at the mechanical floors through outrigger walls in order to maximize the building’s stiffness. The result is an efficient system where all of the building’s vertical structure is used to support both gravity and lateral loads.3 2.2.2. Shanghai tower This tower is second tallest building in the world, its height is 632 meters.

Shanghai Tower is one of the most sustainably advanced tall buildings in the world. A central aspect of its design is the transparent second skin that wraps around the entire building. The ventilated atriums it encloses conserve energy by modulating the temperature within the void.

The space acts as a buffer between the inside and outside, warming up the cool outside air in the winter and dissipating heat from the interior in the summer. The tower also notably employs, a grey water/rainwater system and several renewable energy sources

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http://skyscrapercenter.com/building/burj-khalifa/3

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Elvijs Josts 30.09.2016 Image 7. Shanghai tower in China

Engineers were faced with a lot of challenges – active earthquake zone, a clay based soil and a windy climate. In the center of the building and the heart of the structural system is a concrete core, about 30 meters square. This core is combined together and acts as one with outrigger and supercolumn system. There are four paired supercolumns – two at each end of each orthonormal axis. In addition, four diagonal supercolumns along each 45-degree axis are required by the long distances at the base between the main orthonormal 4 supercolumns . The tower is divided vertically into nine zones, each with 12 to 15 floors. An inner cylindrical tower steps in at each zone, similar to a wedding cake. At the interface of the adjacent zones, a two-story, full floor area is created to house mechanical, electrical and plumbing equipment and also serve as that zone’s life safety refuge area. This full-floor platform creates a base for the atrium spaces directly above.

The skyscraper was designed by Thornton Tomasetti and proposed on 2008, its construction started on 2009 and it was completed by year 2015 in Shanghai, China.

2.3.

Tall buildings in Latvia

In Latvia there are not so many so called skyscrapers, we have some high rise buildings which are at around 120 m tall. Tallest construction in Latvia is our Rīgas radio un televīzijas tornis (Riga`s radio and TV tower), which is a radio and TV tower, its 368.50 m tall and it was completed on 1986. It is not only the tallest tower in Baltic countries, but also the tallest one in Europe, and 13th tallest in the world.

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http://www.ctbuh.org

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Elvijs Josts 30.09.2016 Making this towers foundation, under each of three legs, started by pushing and forcing 20 reinforced concrete pipes till they touch and bases on layer of dolomite. Afterwards these pipes were cleaned out of soil and filled with concrete. Tower is made out of metal elements, which were made in Russia, Chelyabinsk and transported to Latvia by train. These elements were welded together by three, welding was checked very carefully with ultrasound and even x-ray. Afterwards these elements were lifted up with crane and mounted together. Interesting part is that the tip of the tower was made first and was on top all the time, lifted together with the new elements added. The main part of antenna – body – was made on the ground too and lifted up 88 m above and welded to the legs.

Construction took longer than expected and was divided in two parts. Construction started in 1979 and was finished by 1986.

Image 8. Radio and TV tower in Riga

High-rise buildings were not and still being not that popular in Latvia, its most likely because of economic reasons, development and financial problems. But lately, there are some projects being built, of course they are standing nowhere near skyscrapers in United States of America or China. For example, in 2015 project of 2 tall buildings was finished, so called Z Towers, which consists of South and North building, South building being the tallest, reaching 123 meters and North building reaching 117,50 meters. Both towers are for residential use with 341 apartments. Tower is made out of prefabricated concrete elements and cast-in-situ elements.

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Image 9. Z Towers in Riga, Latvia.

3. Construction and design In this section I will mostly research the technical side of tall buildings. Look into history and what are the structural systems of tall buildings. Also I will look and talk about issues and concerns that architects and engineers have to work when designing and constructing tall buildings.

3.1.

Development of structural systems

We can divide the development in three generations: First generation 1780 – 1850: These buildings were constructed out of cast iron columns, often unprotected, for the beams – it was steel and wrought iron being used. Floor partitions were made out of wood. The exterior of such buildings mostly consisted of stone or brick wall, but sometimes for decorative purposes cast iron was added to enrich the design.

Second generation 1850 – 1940: In this period of time, high-rise buildings were constructed using frame structures, where throughout the whole building runs a skeleton of welded or 17

Elvijs Josts 30.09.2016 riveted steel columns and beams, usually covered in concrete. Because of this steel skeleton building has an extremely strong structure, but as this structure goes through out the whole building, interior is not that attractive anymore, its full of heavy load-bearing columns and walls. Their enormous heights at that time were accomplished not through notable technological evolution, but through excessive use of structural materials. Due to the absence of advanced structural analysis techniques, they were quite over-designed.

Third generation 1940 – now: Within this generation there are those of steel-framed construction (core construction and tube construction), reinforced concrete construction (shear wall), and steel-framed reinforced concrete construction. Also hybrid solutions are being used, where it makes use of more than one type of structural system in a building.

Nowadays the development of structural system and construction technologies are developing quite rapid, as there is bigger need and demand for skyscrapers.

3.2.

Design of tall buildings

Visual design very depends on structural system being used in the tall building. Architects have to think how to implement beams, columns or diagonal elements of steel in the buildings design. Nowadays almost always curtain wall is being used in skyscrapers, as it is the best solution to cover steel frame and use this structural frame for as curtain walls frame.

3.3.

Structural systems of tall buildings

Structural systems can be divided in two broad categories: 1. Interior structures 2. Exterior structures The classification is based on where the major part of the lateral load-resisting system is located in the building. In interior structure the major part of lateral load resisting system is located within the interior part of building and vice versa if the major lateral load resisting system is located at the buildings perimeter – exterior structures. However, any interior structure will have some minor components of the lateral load resisting system at the building perimeter, and any exterior structure will have some components within interior of the building.

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Elvijs Josts 30.09.2016 In some skyscrapers engineers have moved the columns and beams from the core of the building to tis perimeter, creating a hollow rigid tube, it’s the same strength as the core design, but weights much less.

Image 10. Exterior structure

Placing steel columns and beams in the core of the building makes a very strong and stiff backbone that can resist strong lateral loads. Also the inner core is used as an elevator shaft, this designs gives a lot of open space in each floor.

Image 11. Interior structure

Interior structures

Figure 3. Interior structures

Braced hinged frames: Braced frames are a very common form of construction, being economic to construct and simple to analyze. Economy comes from the inexpensive, nominally 19

Elvijs Josts 30.09.2016 pinned connections between beams and columns - steel shear trusses + steel hinged frames.

Bracing, which provides stability and resists lateral loads, may be from diagonal steel members or, from a concrete 'core'. In braced construction, beams and columns are designed under vertical load only, assuming the bracing system carries all lateral loads. Braced hinged frames allows shallower beams compared with the rigid frames without diagonals. This system has some disadvantages like interior planning due to diagonals in the sheer trusses and those diagonal connections are expensive. It is efficient for buildings up to 10 stories.

Rigid frames: consists of horizontal (girder) and vertical (column) members rigidly connected together in a planar grid form by moment resistant connections - concrete shear wall plus steel hinged frame. Its members can take bending moment, shear, and axial loads. The size of the columns is mainly controlled by the gravity loads that accumulate towards the base of the building giving rise to progressively larger column sizes towards the base from the roof. The size of the girders, on the other hand, is controlled by stiffness of the frame in order to ensure acceptable lateral sway of the building.5 The advantages of using steel with this structure are that it provides flexibility in floor planning and a fast construction. Efficient height limit is up to 30 stories (but can be higher). Disadvantages are expensive moment connections and expensive fire proofing. Using concrete, the efficient height limit is up to 20 stories, and also provides good flexibility in floor planning and easily moldable although by using concrete you will have to deal with an expensive framework and relatively slow construction. Example: Lake Shore Drive Apartments (Chicago, USA, 26 stories, 82 m).

Shear wall/hinged frames: This structural system has been one of the most popular in being used in tall buildings, as it can very well resist lateral forces like wind and earthquakes with its reinforced concrete shear walls or coupled shear walls. They are treated as vertical cantilevers fixed at the base. When two or more shear walls in the same plane are interconnected by beams or slabs, as is the case with shear walls with door or window openings, the total stiffness of the system exceeds the sum of the individual wall stiffness’s. This is so because the connecting beam forces the walls to act as a single unit by restraining their individual cantilever actions.5 These are known as coupled shear walls. These shear walls are usually located around elevator cores or service shafts, in a lot of buildings, the core walls that are around shafts and building services can be used to stabilize and stiffen the building against lateral loads.

Regarding buildings core location, number, arrangement and shape, there are a lot of possibilities to resist lateral forces and design the building. Materials and configuration are concrete shear wall plus steel hinged frame in this system and building can be efficiently built up to 50 stories. Example: Casselden Place (Melbourne, Australia, 43 stories, 160 m).

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(Moon M. M., 2007)

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Elvijs Josts 30.09.2016 Shear wall (or shear truss) - frame interaction system: This structural system can be divided in two subcategories – braced rigid frames and shear wall / rigid frames. They are both combinations of previous structural systems.

In braced rigid frames they have combined steel shear trusses plus steel rigid frames. It effectively resists lateral loads by producing shear truss - frame interacting system. This effect produces increased lateral rigidity of the building. Efficient height limit – 40 stories. Example: Seagram Building, 17th to 29th floor (New York, USA, 38 stories, 157 m).

In shear wall / rigid frames it can be concrete shear wall plus steel rigid frame or concrete shear wall plus concrete frame. Effectively resists lateral loads by producing shear wall - frame interacting system. Example: Seagram Building, up to the 17th floor (New York, USA, 38 stories, 157 m).

All of these types of systems has wide applications for buildings up to about 40 to 70 stories in height. Yet again the disadvantage of these systems is interior planning limitation due to shear trusses or shear walls. Example: 311 South Wacker Drive (Chicago, USA, 75 stories, 284 m).

Outrigger structures: Outrigger systems are rigid horizontal structures designed to improve a buildings stability and strength by connecting the building core or spine to distant columns. In these structures the core is centrally located in the building with outriggers extending on both sides or in some cases it may be located on one side of the building with outriggers extending to the building columns on the other side. The outriggers are generally in the form of trusses in steel structures, or walls in concrete structures, that effectively act as stiff headers inducing a tension-compression couple in the outer columns. There can be belt trusses provided to distribute these tensile and compressive forces to a large number of exterior frame columns.

This system effectively resists bending by exterior columns connected to outriggers extended from the core. This structural system can contain shear cores (steel trusses or concrete shear walls) plus outriggers (steel trusses or concrete walls) plus (belt trusses) plus steel or concrete composite (super) columns. It is efficient to construct buildings with this system up to 150 stories. Example: Taipei 101 (Taipei, Taiwan, 101 stories, 509 m), Jin Mao Building (Shanghai, China, 88 stories, 421 m).

Exterior structures Exterior structures are much more reliable and has more significance in taller buildings as they are much taller and are more vulnerable to lateral forces, especially wind loads. So to increase the resistance to lateral loads it is much better to concentrate as much lateral load resisting components on the perimeter of building.

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Figure 4. Exterior structures

Tube: The tube system concept is based on the idea that a building can be designed to resist lateral loads by designing it as a hollow cantilever perpendicular to the ground. In simple words, building’s exterior perimeter consists of closely spaced columns that are tied together with deep spandrel beams. This provides a strong structural wall on the perimeter od building, made out of columns and beams.

There are different types of tubular systems.

Framed tube: this is the basic tubular system, where there are closely placed columns and deep spandrel beams rigidly connected together around the perimeter of the building. The columns usually are placed between 1.5 meter to 4.5 meters between each other. This solution also can reduce or completely eliminate need for mullions of the curtain wall, which can significantly reduce the costs of the building. Although the columns narrow column spacing obstructs the view. With concrete famed tube structural system, it is efficient to build up to 60 floors and with steel – up to 80 stories. Example steel construction: Aon Center (Chicago, USA, 83 stories, 346 m). Example concrete construction: Water Tower Place (Chicago, USA, 74 stories, 262 m).

Braced tube: this is a variation of framed tube system; the idea is that instead of using closely placed columns, it is possible to increase the distance and stiffen those more widely placed columns with diagonal braces, also allowing for larger window openings than in the framed tubes. The braces also collect gravity loads from floors and act as inclined columns. It efficiently resists lateral shear by axial forces in the diagonal members. Disadvantages are that the 22

Elvijs Josts 30.09.2016 diagonal bracing obstructs the view from the building. With this system building can be built up till 100 floor high (with interior columns) – 150 (without interior columns) with steel construction and up to 100 floors with concrete construction. Example steel construction: John Hancock Center (Chicago, USA, 100 stories 344 m). Example concrete construction: Onterie Center (Chicago, 58 stories, 174 m).

Bundled tube: it is a group or cluster of individual tubes connected together, so they act as one single unit. Using a single tube for very tall buildings would not be so effective, because of the height-to-width ratio, the base of the building should be quite large so the building would not too much flexible and does not sway too much from lateral loads. The bundled tube concept also allowed for wider column spacing in the tubular walls, which made it possible to place interior frame lines without seriously compromising interior space planning of the building. The bundled tube system thus offers great freedom in the architectural planning by creating a powerful vocabulary for a variety of existing building forms. Steel or concrete buildings can be made using this system, and is efficient to build up to 110 stories high.

Example steel construction: Sears Tower (Chicago, USA, 108 stories, 442 m). Example concrete construction: Carnegie Hall Tower (New York, USA, 62 stories, 230.7 m).

Tube-in-tube: this system works where the framed tube, which is around the buildings perimeter are being enhanced with another tube in the core of the building, this core tube could be made out of a solid tube, a braced tube or a framed tube. It is also possible to add more than one tube inside the building. The inner tubes can be used as a service shafts or elevator shafts. These elements both act in resisting gravity and lateral loads. This second tube, or inner tube, acts as a second line of defense in the building, as if something happens with the perimeter tube, and it fails, the inner tube can still take lateral loads and hold the building up. This system can be made up from external framed tube (steel or concrete) plus internal core tube (steel or concrete) and should be efficient for buildings up to 80 stories. Example: 181 West Madison Street (Chicago, USA, 50 stories, 207 m).

Diagrid system: the name comes from diagonal grid system, where comparing to exteriorbraced frame structures, almost all the vertical columns have been eliminated, making only the diagonal members of diagrid structure around buildings perimeter to carry gravity loads and lateral loads. Compared with conventional framed tubular structures without diagonals, diagrid structures are much more effective in minimizing shear deformation because they carry shear by axial action of the diagonal members, while conventional tubular structures carry shear by the bending of the vertical columns and horizontal spandrels (Moon K. , 2005).

The diagrid structure provides both bending and shear rigidity, comparing to outrigger structures it does not need it does not need high shear rigidly cores, because shear is carried by diagonal elements located around the buildings perimeter. It is possible, for taller buildings 23

Elvijs Josts 30.09.2016 with diagrid system, to add an inner core to strengthen and stiffen the building, making similar system to a tube-in-tube. Advantages of this system is that it efficiently resists lateral loads by axial forces in the diagonal members. Buildings can be constructed from steel up to 100 stories.

Small disadvantage is that there are complicated joints between these diagonal elements.

Using concrete, building can be made up to 60 stories, although it has quite expensive frame work and slow construction compared to steel. Example steel construction: Swiss Re Building (London, UK, 41 stories, 181 m). Example concrete construction: O-14 Building (Dubai, 23 stories, 102 m).

Space truss structures: this space truss structure basically is modified braced tubes system with diagonals connecting the exterior to interior. So as we know in a simple braced tubes structure all the diagonals, which connects the columns are located on the façade of the building, however, in space trusses, some or most of the diagonal elements penetrate the interior of the building. Steel is being used in this structural system as a main material. This system efficiently resists lateral shear by axial forces in the space truss members. Again the disadvantages might be that those diagonals obstruct the view. With such system it is possible to construct buildings up to 150 stories. Example: Bank of China (Hong Kong, China, 72 stories, 367 m).

Superframes: a superframe is composed of megacolumns comprising braced frames of large dimensions at building corners, linked by multistory trusses at about every 15 to 20 stories.

Since the vertical elements (megacolumns) are concentrated in the corner areas of the building, maximum efficiency is obtained for resisting wind as exterior tubular structure.

Superframe structures can create ultra-high-rise buildings up to 160 stories from steel and up 100 stories from concrete. The main advantage of this structural system is the amazing heights it can provide for buildings. Example steel construction: Chicago World Trade Center (Chicago, USA, 168 stories, Unbuilt). Example of concrete construction: Parque Central Tower (Caracas, Venezuela, 56 stories, 221 m).

Exoskeleton: structural system which takes lateral loads is placed outside the building, meaning away from building’s façade. As the system is placed outside the building, there is no serious issue of fire proofing it. Main advantage of such structure is that the interior of building is never obstructed by perimeter columns and if designed properly, the exoskeleton can give a nice aesthetic look for the building. The main disadvantage is thermal expansion and contraction of the exoskeleton, which can be affected by weather changes, so this should be carefully taken into consideration when designing such building. This structure is being built with steel and can raise a building up to 100 stories. Example: Hotel de las Artes (Barcelona, Spain, 43 stories, 137 m).

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Elvijs Josts 30.09.2016 For the tallest building now – Burj Khalifa, there was a unique structural system developed, which they called Butressed core. In this system the lateral loads and gravity loads are shared equally between the interior core and perimeter structural systems linked by the link beam which makes the structure super strong. It consists of high performance concrete wall construction. Each of the wings buttress the others via a six-sided central core, or hexagonal hub. This central core provides the torsional resistance of the structure, similar to a closed pipe or axle. Corridor walls extend from the central core to near the end of each wing, terminating in thickened hammer head walls. These corridor walls and hammerhead walls behave similar to the webs and flanges of a beam to resist the wind shears and moments.

Perimeter columns and flat plate floor construction complete the system. At mechanical floors, outrigger walls are provided to link the perimeter columns to the interior wall system, allowing the perimeter columns to participate in the lateral load resistance of the structure; hence, all of the vertical concrete is utilized to support both gravity and lateral loads. The result is a tower that is extremely stiff laterally and torsionally. It is also a very efficient structure in that the gravity load resisting system has been utilized so as to maximize its use in resisting lateral loads.6

3.4.

Issues and concerns in tall buildings

Stability of a tall building is one of the main concerns a tall buildings skeleton can be seen as a vertical beam; which base is fixed in the ground. The buildings structure has to be able to carry vertical gravity loads, earthquake loads and lateral wind. Gravity loads are divided in dead and live loads. The dead load includes the weight of building itself, immovable structures such as walls and roof. Dead loads are also known as static or permanent loads. Live loads or imposed loads are temporary loads, like workers or residents and goods in the building, also a snow load or impact load. Lateral loads tend to snap the building or topple it (wind load, earthquake). The building must therefore have adequate shear and bending resistance and must not lose its vertical load-carrying capability. So it is very important to use a proper and tested materials in tall building construction as well as proper and tested structural system, which can provide stability for the building. I have researched and talked about structural systems in previous paragraphs.

Gravity In normal buildings made of bricks and mortar, you have to keep thickening the lower walls as you build new upper floors. After you reach a certain height, this is highly impractical. If there's almost no room on the lower floors, what's the point in making a tall building? Using this technology, people didn't construct many buildings more than 10 stories -- it just wasn't 6

http://www.burjkhalifa.ae/en/the-tower/structures.aspx

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Elvijs Josts 30.09.2016 feasible. But in the late 1800s, a number of advancements and circumstances converged, and engineers were able to break the upper limit.

Steel an iron development in constructing buildings was the main technological advancement.

In beginning there were mostly used long beams of solid iron, which gave architects some new possibilities. These new, relatively lightweight metal beams could support much more weight than old brick and mortar walls in old buildings and at the same time taking up a fraction of space the old walls did. Steel, which is even lighter and stronger than iron, made it possible to build even taller buildings.

Wind Skyscrapers also have to deal with the horizontal force of wind. Most of the skyscrapers can move up to half meter in each direction. What we have to think now is how it affects occupants, as the occupants of the building would feel this much horizontal movement.

To control this horizontal sway, the most basic method is being used, where the structure of building is simply tightening up. At the point where the horizontal girders attach to the vertical column, the construction crew bolts and welds them on the top and bottom, as well as the side. This makes the entire steel super structure move more as one unit, like a pole, as opposed to a flexible skeleton.

For taller skyscrapers, tighter connections don't really do the trick. To keep these buildings from swaying heavily, engineers have to construct especially strong cores through the center of the building. In the Empire State Building, the Chrysler Building and other skyscrapers from that era, the area around the central elevator shafts is fortified by a sturdy steel truss, braced with diagonal beams. Most recent buildings have one or more concrete cores built into the center of the building.

Some buildings already use advanced wind-compensating dampers. Oil hydraulic systems push a 400-ton concrete weight back and forth on one of the top floors, shifting the weight of the entire building from side to side. A sophisticated computer system carefully monitors how the wind is shifting the building and moves the weight accordingly. Some similar systems shift the building's weight based on the movement of giant pendulums. These solutions are also being used in case of earthquakes.

The effects of wind can also be minimized by aerodynamic shaping of the building. Wind tunnel testing considers appropriate loading for overall lateral system design and cladding design, and predicts motion perception and pedestrian level effects.

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Elvijs Josts 30.09.2016 Earthquakes Depending on which region or country the tall building is being built, engineers have to consider the possibilities of earthquakes and other natures disasters, and be sure that these tall buildings can withstand them. As I described before, earthquakes put a lateral, or sideways, load to the building structure that is a bit more complicated to account for. One way to make a simple structure more resistant to these lateral forces is to tie the walls, floor, roof, and foundations into a rigid box that holds together when shaken by a quake, so it is a solid strong box. As the buildings get bigger and taller other techniques are employed such as “base isolation.” During the past 30 years, engineers have constructed skyscrapers that float on systems of ball bearings, springs and padded cylinders. Acting like shock absorbers in a car, these systems allow the building to be decoupled from the shaking of the ground. Another technique to dampen the swaying of a tall building is to build in a large (several tons) mass that can sway at the top of the building in opposition to the building sway. Known as “tuned mass dampers”, these devices can reduce the sway of a building up to 30 to 40 percent. The Taipei 101, formerly known as the Taipei World Financial Center, has just such a giant pendulum mounted between the 88th and 92nd floors. Weighing in at 730 tons and capable of moving 1.5 meters in any direction, it takes the prize as the world’s largest and heaviest building damper. In fact, it is so heavy that it had to be constructed on site since it is too heavy to be lifted by a crane.

Terrorism Terrorism is a big problem an issue for tall buildings, as they are great targets for attacks filled with people. Engineers and architects have to make a building that can withstand blast load and impact load. Buildings have to be made much stronger as well as there has to be a fast and good evacuation plan and possibilities planned. Tube-in-tube structural system is a good solution, because if the external perimeter tube is being compromised, the inner (core) tube can still hold the building up and give so much valuable time for people to evacuate.

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Image 12. Tuned mass damper in Taipei 101 in Taipei, Taiwan

Elevators Elevators are an important part of a skyscraper, and it is understandable why, as most people, including me, wouldn’t want to climb up more than 10 flights of stairs at the time, not even thinking stairs up to 160th floor. But there is an elevator conundrum. As the buildings get taller and provides apartments and with more floors you increase buildings occupancy. When there are more people you obviously need more elevators to service additional people and floors.

But the elevator shafts take up a lot of room, so you lose floor space for every elevator you add. To make more room for people, you have to add more floors. Deciding on the right number of floors and elevators is one of the most important parts of designing a building.

One way how architects and engineers deal with this is to put elevator shafts on top of each other in order to save that crucial space. In some buildings there are so called sky lobbies, where express elevators bring people up to upper floors. So there is a main elevator bringing people up to sky lobby from where people can get up to the upper floors with express elevator.

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Elvijs Josts 30.09.2016 Fire Fire safety is a very important issue and skyscrapers wouldn’t have worked so great without the advent of new fire-resistant building materials in 1800s. If fire breaks loose in skyscrapers the most obvious problem is that fire man’s water hoses are often unable to reach the fire, their fire hoses can spray water up to maximum 30 meters. Therefor fire-fighters have to enter the building and reach the area with the fire, which takes time and in this time fire could spread more.

To combat this, engineers and architects design the buildings so that fires are contained, limiting the spread of flames, gas or smoke in a process known as “fire compartmentation”.

The main idea behind this is that any fire that outbreaks in the building should be able to burn itself out without any external intervention, and without the building collapsing and at the same time residents could safely evacuate the building. Also these days, skyscrapers are equipped with sophisticated sprinklers that puts out most fires before they can spread very far.

4. Reasoning behind tall buildings and skyscrapers Up to the Industrial Revolution people all over the world lived mainly in the countryside. In 1800, only 3 % of the world’s population lived in cities. During industrial revolution, millions of villagers moved from a village to a city, in hope to find a work. In 1900 only 12 cities had more than 1 million people. Small and cheap housing was the solution to this migration.

Engineers and architects realize that it is important to save so valuable space in the city and started to build up vertically. In late 19th century tall building development was mostly based on economical point of view – building vertically, expanding office space and maximizing rent income. But later they also started to build residential housing.

In 1995, there were 22 large cities, and 14 megacities globally; by 2015, both categories of cities had doubled, with 22, or 79 per cent of the megacities located in Latin America, Asia and Africa. The fastest growing urban centers are the medium and small cities with less than one million inhabitants, which account for 59 per cent of the world’s urban population.

Urbanization has become an increasingly critical issue as 59 percent of the world population lives in urban areas and is predicted to continue growing to 70 percent by 2050 (UN study, 2014). This means there will be need for more workplaces and housings, tall buildings are a good solution to this problem – expanding city vertically and also making a beautiful skyline.

Denser cities with megastructures are more efficient in terms of energy consumption and land use. So it is important to develop better and cheaper ways to build tall structures and help the cities to accommodate all the people.

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Elvijs Josts 30.09.2016 Tall building development also involves various complex factors such as economics, architectural style, technology, municipal regulations, and politics. Among these, economics has been the primary governing factor since the emergence of the skyscrapers in the late 19"t century.

4.1.

Advantages and disadvantages of tall buildings

The main advantages of tall buildings:   

Helps city to expand vertically, saving so much valuable space and can accommodate more residents, compared to shorter buildings Living in higher floors will be more isolated and provide more peaceful and uninterrupted living Building tall buildings pushes our limits and pushes us to improve technologies and ways to build, which helps to develop constructions and structures

The main disadvantages of tall buildings:      

Constructing tall buildings require highly skilled engineers and architects to design the building, which drastically increases the total cost of building.

High costs of repair and maintenance High power consumption (although nowadays tall buildings are becoming more selfsustainable) Shading effects on adjacent buildings In crisis of total power outage, taking stairs can be a big issue Terrorists most likely to target tall buildings.

5. Sustainability in tall buildings When talking about Skyscrapers, one of the main issues many architects talk about are sustainability. Compared to the beginnings of tall buildings, we can see that sustainability has become a big factor in designing such buildings. Technologies and sustainable solutions also have developed and increased. People are demanding greener and sustainable buildings therefore architects and engineers are trying to deliver. In a perfect world, skyscraper would be able to generating enough energy to serve its own needs and also pumping enough back into the grid to make up for the carbon that was emitted to build it, at the moment that is not possible, but that is where we are trying to get. There are already a lot of good sustainable solutions out there, that are being used all over the world. Also a lot of issues and problems that have not been solved yet.

One of the biggest issue in skyscrapers from sustainable point of view is consumption of concrete and steel. Constructing such buildings uses a lot energy. Concrete and steel have a 30

Elvijs Josts 30.09.2016 large carbon footprint and are highly energy intensive materials to produce. Around 5% of world carbon dioxide emissions are from producing concrete. Nevertheless, these materials are somewhat reusable. Steel is more sustainable in this way, as it can be reused if the building is being demolished. With concrete its more difficult and reusing it uses much more energy and is not worth it. One solution for this problem could be using timber in construction. This method has been proven and already used in some projects – making structural system out of wooden elements. Timber can remove CO2 from our atmosphere, storing the carbon and giving us in return oxygen. For this structural sustainability it is important to also try to use recycled materials, use local manufacturers as less travel distance for materials to building site equals less pollution.

There is a lot of energy spent in maintaining tall buildings, to cool, ventilate and to light them up. So sustainable solutions have to be implemented. Such solutions as photovoltaic panels, natural ventilation, and a biogas generation plant. Some tall buildings even use wind power and have a wind turbine, although it is a hard task to implement this in the design of the building so this solution is not quite popular. But using photovoltaic panels or PV panels is a very common and popular sustainable solution, as they can be easily implemented in design.

Technology has developed so far that there is even a see through PV panels, which may not yet be completely clear as glass, but still can let through enough light and also produce energy for the building. To help the ventilation – natural ventilation is introduced, with opened atriums and green walls to increase bio-diversity, which also decreases the carbon footprint of a skyscraper. A lot of the building are collect rainwater and integrate a grey-water system for both plant irrigation and toilet flushing.

Sewer and MEP. One of the biggest extra costs are sewers, ventilation system and piping.

Extra-long piping and ventilation system brings extra weight to the structure, increases shaft area, increases ceiling height which all in the end increase consumption of building materials.

“Skyscrapers create high-density environments for living and working in, which facilitates sustainable transport and sustainable urban planning, they create a scale of development which can make things like more energy-efficient technologies, like district cooling, more feasible. So, it’s definitely possible to have skyscrapers which are sustainable and costeffective.” Mr Alabbar – designer of Abu Dhabi`s Al Bahar Towers.7 As we can see there are already a lot of sustainable solutions and advantages in tall buildings, but of course there is still a long way till completely self-sustainable building and a building that can produce more than it uses, but we are on the right track.

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6. Future of tall buildings Seeing how fast technology is developing and demand of tall buildings are growing, because of migration in populations from rural areas to urban, has resulted in high-density mega cities.

We can only imagine what kind of structural wonders awaits us in the future. But we can for sure say that the race continues, Burj Khalifa might be the highest structure built, reaching 829.8 meters, but for how long will it be the tallest. There are some envisioned projects, that most likely will not be built any time soon or built at all.

6.1.

Under construction Image 13. Jeddah Tower in Jeddah, Saudi Arabia

There are quite a lot of skyscrapers that are under construction at the moment, but I will only talk about one. Its name is going to be Jeddah Tower (Kingdom Tower), and it is located in Jeddah city, Saudi Arabia.

Why exactly is this one worth mentioning? It is because this will be the tallest building built in year 2019, of course of the construction goes as planned and building is finished on time. This building is planned to be 1000+ meters tall, which is an amazing height and will overtake Burj Khalifa by 170 meters. This building was proposed on 2011, and its construction started on 2013. It is designed to have around 439 apartments, 200 hotel rooms and 2205 parking places.

Structural system for this tower is very similar to Burj Khalifa, the multivariate form of the tower is rationalized by a “Y�-shaped plan and a continuously smooth taper, which will significantly reduce structural loads by obviating the need for the complicated outrigger transfers and belt trusses required in a setback approach.

Furthermore, each wing of the tower will terminate at different heights, allowing them to taper at different rates and establish a distinct three-part spire. The supporting structure for the building is comprised entirely of cast-in-place reinforced concrete walls, coupling beams, and conventionally reinforced plate concrete floor framing. Due to the continuous and uninterrupted vertical nature of the walls, a highly efficient jump form system is utilized that will permit a continuous and uninterrupted construction process.8

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6.2.

Envisioned tall buildings

Image 14. Tallest buildings ever proposed.

In the image above you can see highest buildings built in comparison of some envisioned projects. Which most likely will not be built any time soon, because of lack of technology and resources. But that does not stop architects and engineers to dream and envision such structures. That is what keeps us pushing, keeps us to develop technology and structural systems The X-Seed 4000 is the tallest building ever fully envisioned, meaning that the designs for the building have been finished. It is proposed to be 4000 meters high and 6000 meters wide sea base with 800 stories, and could accommodate up to 1 000 000 people. It was designed in Tokyo, Japan in 1995. The structure would be built of over 3 000 000 tons of steel. Of course there are a lot of unsolved issues and problems with such a structure, for example to maintain suitable indoor climate and environmental conditions for people and to protect people from considerable air pressure because of its massive height. Some estimate that it could cost $587 billion–$1.06 trillion, which is a ridiculous amount of money.

Similar project is Ultima Tower, which is envision to be 3218 meters tall and would have 500 stories. The shape of the building draws inspiration from the nests of termites, a 1-mile wide funnel shape with gently curved sides. A criss-crossing network of double-helix cables distributes tension across the outer covering in such a way as to allow the entire building to absorb stresses instead of single areas. The design is extremely aerodynamically efficient, and resistant to earthquake shock waves. The structure is cooled in a similar way to a termite nest - the lower levels are cooled by water flow (in this case, a series of ground-floor waterfalls)

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Elvijs Josts 30.09.2016 and the cool air rises through the building, taking heat energy with it, and exits at the upper floors into the atmosphere.9 As we can all the envisioned projects have somewhat similar shape, pyramidal shape, as here comes in the height-to-width ratio, for the structure to be able to be stable and stiff and carry its own weight, the base has to be much thicker. But as population pressure increases, it's pioneering ideas like these that will form the inspiration for real-world solutions.

7. Conclusion We have come a long way since the beginning of building, our unstoppable will to build better, build taller, build bigger has lead us here where we are. If in the beginning these big structural wonders were built to show power and superiority, or to impress and satisfy our leaders and gods – Great Pyramids of Giza, now it is the need of housing, need of workplaces and to save so much valuable space in cities by expanding vertically as well as endless competition between architects and engineers to build the tallest building. But we had a long way till where we are.

A structural revolution – the steel skeletal structure – as well as consequent glass curtain wall systems, which occurred in Chicago, has led to the present state-of-the-art skyscraper. I like to think these were two of the most important steps towards constructing tall buildings. Of course before these concepts there were tall buildings made out of stone (even up to 10 stories high), but people fast realized that this is not a good solution for constructing taller buildings, as the walls at the base of the building had to be very thick to support the weight of the upper walls and building itself. When iron, and later steel, were started to be used in construction and building tall buildings, it changed everything, as they could build much stronger and lighter structures, with less material. The beginning of these braced frame structures, which were firstly used to produce more rentable office spaces in United States of America, developed and took their evolutionary path up to the present towards more efficient and even taller structures. Tall buildings, which began from with 10-story office towers in the late nineteenth century, have evolved to megastructures like the Burj Dubai. But to get there we also had to develop different kinds of structural systems, for the buildings to be so tall and be able to withstand both gravity loads and lateral loads. With stronger and better quality materials and the knowledge of previous buildings and some failures, we are able to develop and make much stronger and reliable structural systems. We have developed from braced hinged frames and rigid frames where we could build up to 30 stories tall buildings, to space

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Elvijs Josts 30.09.2016 truss structures and superframe structures where we can build up to 160 stories tall buildings.

But what exactly pushes us to make these wonderful buildings?

The need to build upwards are increasing because populations worldwide are growing rapidly and migration to urban areas from rural areas are increasing, UN predicts that by year 2050 70% of world’s population will live in cities or megacities. As I mentioned before tall buildings helps city to expand vertically, saving so much valuable space and can accommodate more residents, compared to shorter buildings. We can also say that it makes cities more sustainable. These denser cities with megastructures – skyscrapers – are more efficient in terms of energy being consumed and land used. The power grid becomes smaller which makes the transfer of electrical energy more efficient (we lose a lot of electrical energy just by transferring it through the grid, up to 15%). Also It helps to reduce loads on traffic, as the need for automobile transportation declines, which declines pollution. By creating denser cities with skyscrapers we can save more natural green areas globally.

There is a big future and a lot of possibilities regarding tall structures and skyscrapers, as technology keeps developing and will of architects and engineers to build the tallest building and compete in never-ending competition, will keep them busy and us impressed with the future wonders of these megastructures.

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Bibliography Ali, M. M. (2001). Art of the Skyscraper: the Genius of Fazlur Khan. New York: Rizzoli.

Archengine. (n.d.). http://www.archengine.com. Retrieved from http://www.archengine.com/book/sustainable-skyscrapers/ Burj, K. (n.d.). Retrieved from http://www.burjkhalifa.ae/en/the-tower/structures.aspx Crystalinks. (n.d.). Retrieved from http://www.crystalinks.com/ziggurat.html Fletcher, B. (2001). A History of Architecture on the Comparative method. Elsevier Science & Technology. http://skyscrapercenter.com/building/burj-khalifa/3. (n.d.). Retrieved from http://skyscrapercenter.com/building/burj-khalifa/3 Khan, F. R. (1965). Design of high-rise buildings. Chicago, Illinois: Universitu of Chicago.

Moon, K. (2005). Dynamic Interrelationship between Technology and Architecture in Tall Buildings.

Moon, M. M. (2007, June 13). Structural Developments in Tall Buildings: Current Trends and Future Prospects. Retrieved from http://sydney.edu.au/architecture/documents/publications/ASR/Structural%20Devel opments%20in%20Tall%20Buildings.pdf newatlas. (n.d.). http://newatlas.com. Retrieved from http://newatlas.com/ultima-towereugene-tsui-population-challenge/9262/ Rasels, E. (2000). Lielie Pasaules BrÄŤnumi. Riga: Zvaigzne ABC. Skyscraper Center. (n.d.). Retrieved from http://skyscrapercenter.com/ thenational. (n.d.). http://www.thenational.ae. Retrieved from http://www.thenational.ae/business/industry-insights/property/uae-sustainableskyscrapers-understanding-abu-dhabis-al-bahar-towers#page1

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