Tall Wood Buildings. Design, Construction and Performance. Second and expanded edition

This publication provides a systematic introduction to the tech­ nology and explains typical Tall Wood constructions such as panel systems, frame and hybrid systems. An international selection of 18 best-practice case studies is documented in detail with many specially prepared construction drawings, demonstrating the range of the technology.

Both authors are experienced specialists for timber construction: Michael Green (MGA | Michael Green Architecture), Vancouver, and Director of the non-for-profit school DBR | Design Build Research, is a researcher and practitioner in the field of timber structures. His 2013 TED talk, viewed over 1.3 million times, made a large audience aware of Tall Wood buildings.

Jim Taggart, Vancouver, is an architect, publicist and editor of Sustainable Architecture and Building Magazine. He has taught architecture at the British Columbia Institute of Technology in Vancouver since 2004. He is also the author of the awardwinning books Toward a Culture of Wood Architecture (2004) and The Architecture of Engagement (2019).

TALL WOOD BUILDINGS

Over the last decade, Tall Wood buildings have been at the forefront of innovative building practice in urban contexts. In many cities around the globe, these timber high-rises have emerged as a new urban element. Mass timber buildings of up to 20 storeys and a height of 85 meters have been built, are under construction or being considered. This dynamic shift has been enabled by the emergence of new engineered wood products, prefabrication and more flexibility in fire regulations. The low carbon dioxide footprint of wood – often regionally sourced – make it a responsible choice for today’s buildings.

MICHAEL GREEN JIM TAGGART

www.birkhauser.com

MICHAEL GREEN JIM TAGGART

TALL WOOD BUILDINGS DESIGN, CONSTRUCTION AND PERFORMANCE

SECOND AND EXPANDED EDITION

TALL WOOD BUILDINGS DESIGN, CONSTRUCTION AND PERFORMANCE MICHAEL GREEN JIM TAGGART

Second and expanded edition

Birkhäuser Basel

MATERIALS The barriers to building taller with wood have been both legislative and perceptual. Even as prescriptive building codes give way to objective-based ones, concerns about the strength and durability of wood remain – if not with architects and engineers, then with approving authorities, developers and the public. After all, the wood with which they are familiar is a soft, ­organic material, susceptible both to physical damage by fire and to decay if allowed to remain wet for a prolonged period of time.

While this may be true for solid sawn material in its natural state, the properties and performance of wood can be modified to a significant degree by modern processing methods. Engineered massive wood products, such as cross-laminated timber (CLT), laminated veneer lumber (LVL), laminated strand lumber (LSL)

and parallel strand lumber (PSL), are now available alongside glue-laminated timber (glulam), and are stronger, more consistent and more dimensionally stable than traditional solid sawn material. However, even with these modified properties, an understanding of the intrinsic characteristics of wood remains critical to the successful design of Tall Wood buildings.

PROPERTIES OF WOOD

Most important among the properties of wood is the fact that, as an organic material with a cellular structure, its strength and stability vary with orientation of grain and moisture content. Controlling these two ­variables is key to creating components and structures that are precise, dimensionally stable, strong and ultimately more durable.

3 Materials | 27

Glue-laminated timber (glulam) is fabricated by

Glue-laminated timber panels have the appearance of glulam

gluing individual pieces of dimensional lumber

beams laid flat. These panels provide a strong and economi-

together to form columns, beams and headers.

cal flooring option with one-way spanning capability.

out failure. The different types of load to which a structural component may be subjected are: compression, tension, bending, shear and torsion. The strength of wood varies according to the direction in which a force is applied to it. The material is strongest in tension and compression parallel to grain (that is when the force is applied along the fibres), and much weaker (typically by a factor of ten) when the force is applied perpendicular or tangential to grain.

The strength of wood varies between species: western red cedar may have a compressive strength of around 1100kPa (kilo Pascals), Douglas fir a strength of around 1800kPa and mahogany a strength of around 3600kPa. In addition, the natural variability of wood (which may include tighter or more open grain, as well as the presence of minor defects such as splits, checks and knots) means that for solid sawn wood products there can be considerable variation in these figures. Since this inconsistency of natural wood makes the predictability of performance difficult, wood industry researchers around the world have spent decades on the development of engineered wood products (EWPs), with the aim of increasing the strength of wood and reducing variation.

centage of the tree to be used than would be possible with solid sawn lumber. In addition, because the wood or wood fibre used in the manufacturing process is kilndried, engineered wood products, are dimensionally stable and can be fabricated to precise specifications.

The two most familiar EWPs are plywood and glulam, both of which have been in common use since the ­early 1900s. In the last three decades, they have been joined by a range of new massive wood products, which (like glulams) lend themselves to the construction of Tall Wood buildings.

Accordingly, the descriptions that follow relate to the massive panel and beam products used in Tall Wood construction. Because these products are manufactured under controlled conditions using a variety of bonding and pressing techniques, they can typically be produced in a range of standard thicknesses, in widths up to 2.5 or 3.0 metres, and in lengths limited only by the constraints of road transportation.

ENGINEERED WOOD PRODUCTS

EWPs are manufactured by bonding together wood strands, veneers, small sections of solid lumber or other forms of wood fibre to produce a larger and integral composite unit that is stronger and stiffer than the sum of its parts.

The material that makes up engineered wood products can generally be obtained from smaller trees, and the manufacturing process enables a much greater per-

Glue-Laminated Timber Glulam [ill. p. 29) is manufactured by gluing together

individual pieces of dimension lumber under controlled conditions to form larger linear elements. In Tall Wood buildings glulam is used for columns, beams, headers, and in the cases of Treet [pp. 182– 187] and Mjøstårnet [pp. 150–157] structural trusses were fabricated from glulam.

While the process of glulam fabrication remains fundamentally the same as when first introduced in ­Germany in 1906, the lumber used today is a select high-strength grade, known as ‘lamstock’. Lamstock is available in three grades, the highest being L1 and the lowest being L3.

3 Materials | 29

Laminated veneer lumber (LVL) is fabricated by laminating and gluing multiple veneers together in the same orientation. This enables long elements to be produced that have high strength in one direction.

Laminated strand lumber (LSL) is fabricated from flaked wood strands glued together in large billets. The length is limited only by standard shipping and trucking dimensions. LSL can be used for floors, walls and vertical members where large floor-to-floor heights are required.

Parallel strand lumber (PSL) is fabricated from long strands of veneer pressed and glued into standard dimensions and lengths. It has very consistent properties and high strength.

30 | PRINCIPLES OF TALL WOOD BUILDINGS

In North America, glulam has traditionally been made from Douglas fir, SPF (spruce/pine/fir), larch (Larix decidua) or southern yellow pine. However for exterior applications it is now possible to obtain glulam made from Alaskan yellow cedar. In Northern Europe and Russia, red pine (Pinus resinosa) and white spruce are the most common species used for the manufacture of glulam.

Lamstock is typically supplied in nominal thicknesses of 25 or 34mm and (according to species and country of origin) widths of 80 to 170mm. Lengths are typically 3 metres or longer, with pieces being finger-jointed­ and glued together as necessary. The lamstock is kilndried to a moisture content of between 10 and 14%, then end-glued together to attain the required length.

The multiple laminations are then face-glued together under pressure in a jig that (if required) gives the final product the desired camber, curvature or taper.

Glulams can be fabricated to any length, enabling them to be used for long free spans, or continuous spans over multiple points of support. They can also be used for columns that extend over multiple floors.

Glulam beams are normally laid up so that they are in the vertical orientation when loaded (i.e. the load is applied perpendicular to the long face of the laminations).­In such cases, the upper and lower laminations may be specified to have a higher strength class than the centre laminations, as these are the parts of the beam where compressive and tensile forces are greatest.

Nordic, an engineered wood products manufacturer in northern Quebec makes glue-laminated products using small-dimension square sections cut from the tips of black spruce trees. The sections are then glued ­together both horizontally and vertically to make ­glulam beams, columns and panels that have a distinctive checkerboard cross section. This material was used for the columns, beams and floor panels of the six-storey FondAction CSN Building in Quebec City, designed­by GHA – Gilles Huot Architecte and completed in 2010 [ill. p. 36]. Glulam can be supplied in a variety of appearance grades for concealed or exposed

FRAME SYSTEMS Frame systems, in which vertical loads are carried by an interconnected system of beams and columns, lend themselves naturally to building programs that require larger and more flexible interior spaces, typically commercial, institutional and assembly occupancies.

Frame systems provide the opportunity for larger areas of glazing and therefore a different architectural expression than that associated with residential buildings. They also require additional measures, such as cross bracing or shear walls, to address issues of lateral stability.

Different approaches to the design of frame systems are illustrated in the following portfolio of projects:

closely resembles that of late 19th and early 20th century commercial buildings.

– At the Wood Innovation and Design Centre lateral stability for the glulam post-and-beam frame is provided by the CLT elevator shaft and stair cores.

– With glulam frame and NLT panel construction, T3 Minneapolis has similarities with the Bullitt Center.

Where it differs is in its response to its historic warehouse context and its strategy for minimizing the visual impact of exposed services.

– In Brisbane, 25 King Street Office Building employs a glulam frame to resist vertical loads, with CLT floor diaphragms and diagonal glulam cross bracing to resist lateral forces. Visible through the glazed cur-

– The Earth Sciences Building combines a traditional post-and-beam frame with contemporary approaches to connection design and wood/concrete composite construction.

– The Tamedia Head Office exploits the potential of

tain wall, the cross bracing adds a dynamic quality to the building.

– The 85.4-metre tall Mjøstårnet building in Norway combines a perimeter structure of vertical glulam trusses, with an interior structure of glulam posts

digital fabrication to create a structure inspired by

and prefabricated glulam and LVL floor panels.

traditional Japanese joinery techniques.

­Concrete floors on the upper levels improve the

– The Bullitt Center has a glulam post-and-beam structure and nail-laminated floor panel construction that

102 | CASE STUDIES: 9 FRAME SYSTEMS

­dynamic performance of the building.

| 103

MJØSTÅRNET Brumunddal, Norway

[Voll Arkitekter] 2019 Year AB Invest A/S Client Sweco Structural Engineer Moelven Limtre Engineered Wood Fabricator/Installer HENT Contractor Moelven Limtre Glulam Supplier Stora Enso CLT Supplier

Overlooking a lake in rural Norway, the world’s tallest wood building in 2019 was conceived and constructed using local design expertise, manufacturing technology, labour and materials.

150 | CASE STUDIES: 9 FRAME SYSTEMS

Metsä Wood LVL Supplier Mixed Residential/Commercial Program

Measuring 85.4 metres to the top of the pergola, Mjøstårnet is considered the tallest timber building in the world to date.

This 18-storey, 85.4-metre mixed-use tower is located in the small town of Brumunddal, about 140 kilometres north of Oslo. The building, which includes offices, 32 apartments, 72 hotel rooms, a restaurant and a rooftop terrace, stands on the shore of Lake Mjøsa, with panoramic views of the surrounding farmland, forests and hills. The economic drivers for the region are tourism, agriculture and forestry.

The inspiration and impetus for Mjøstårnet came from local investor Arthur Buchardt, who wanted to build the world’s tallest timber building using local resour­ ces, local suppliers, local expertise and sustainable wood products. Buchardt’s dream was realized in March 2019 with the opening of Mjøstårnet, whose primary glulam structure was fabricated by Moelven Limtre, just 15 kilometres from the site, using locally harvested, sustainably managed Norway spruce.

CONCEPT

With both buildings being engineered by Sweco, there are similarities between the structural concept for Mjøstårnet and that of Norway’s other notable Tall Wood building, Treet in Bergen (pp. 182–187). However, there are also significant differences as a result of Mjøstårnet’s much greater height and its mixed program.

Both buildings have large vertically oriented glulam trusses around the perimeter that resist both lateral and uplift forces. They also have secondary load-bearing CLT elevator and stair shafts, but these do not form part of the lateral system. Whereas Treet uses stacked volumetric apartment modules supported on intermediate ‘power floors’, Mjøstårnet has a more conventional interior structure of glulam columns and beams supporting prefabricated concrete and LVL/glulam

Mjøstårnet | 151

Glulam brace and beam meeting corner column

Finished hotel suite interior

2

2

3

4

4

5

6

5

4

1

Fifth floor plan (office space)

1 Office space 2 Stair 3 Elevator core

8

2

4 Services

2

7

5 Washrooms

3

6 Storage

7

7

7 Apartment vestibules

7

8 Apartment unit

7

7

9 Balconies

8

8

9

12th floor plan (residential)

152 | CASE STUDIES: 9 FRAME SYSTEMS

9

8

9

8

8

9

9

View of the ground floor dining area

floor panels. The column and beam system provides the longer spans and spatial flexibility required for the offices and the larger spaces in the hotel.

The façade consists of prefabricated, high-performance sandwich panels that were supplied with both interior and exterior finishes and secured to the outside of the glulam truss structure. Like the interior CLT walls, these panels do not form part of the building’s lateral system.

CONSTRUCTION

The building footprint is approximately 17 x 37 metres, taking the form of a concrete ground slab sup-

ported on piles driven to bedrock. The glulam superstructure was constructed on this solid platform.

Unlike at Treet, where glulam trusses were prefabri­ cated off-site, the individual truss members for Mjøstårnet were coded, bundled together and shipped to site, without any trial assembly. Given the complexity of the joinery, the uniqueness of each piece and the precision required, this represented a considerable risk. However, only one out of several hundred glulams needed to be re-machined, so the anticipated savings in transportation costs, fabrication and erection time were successfully realized.

Mjøstårnet | 153

1 2 2 3

4

5 6 7 8

9

9 10

Typical floor plate to wall connection 1 Thermally and fire-retardant treated pine cladding and back-up support 2 Mineral

wool insulation 3 Exterior sheathing 4 Flashing on support as part of the prefabricated wall panel 5 Steel angle 6 Concrete topping 7 Floor panel LVL top plate 8 Glulam edge beam 9 Floor panel glulam joists and flanges 10 Gypsum plasterboard

During construction, the top of the CLT panels and the end grain of glulam columns and diagonal braces were temporarily protected from the weather with plastic. When installation of the exterior wall panels was completed, moisture metres were used to ensure that the wood components had dried sufficiently before being covered or enclosed.

However, the majority of the structure remains exposed to view. The required two-hour fire resistance for the glulam structure is achieved through the charring method, with members being oversized by approximately 80mm in each dimension. The largest columns are at the corners of the building (where axial forces are greatest) – these being 1485mm × 625 mm.

Interior columns are 725mm × 810mm and 625mm × 630mm.

All glulam elements are connected using slotted-in steel plates and dowels, a high-capacity system commonly used in bridges. With the exception of the rooftop pergola, all the structural timber is inside the façade, visible in places from the outside, but protected from the weather.

154 | CASE STUDIES: 9 FRAME SYSTEMS

The wooden floor elements were fabricated by Moelven, which refers to this as its ‘Trä8’ system. They ­consist of glulam beams with LVL panels glued to the top. The voids are filled with Rockwool® and have a 90-minute fire resistance rating. At Mjøstårnet the maximum span is 7.5 metres, although the system is capable of spanning up to 10 metres. Most of the panels have a 50mm thick concrete topping to improve acoustic performance.

On levels 12–18, these prefabricated wood floors are replaced with 300mm thick concrete slabs. The concrete increases the weight of the building (and hence its mass of inertia). This limits the horizontal accelerations at the top of the building under wind load to the recommended comfort criteria for building occupants. The horizontal deflection at the top under maximum wind load is 140mm.

Originally, the project was designed with an overall height of 81 metres, however, well into the design process and after the foundations had been completed, the client challenged the design team to increase the size and height of the rooftop pergola. With both the

Detail of glulam beam and column during construction, forming

Detail of chevron bracing system during construction. Metal

a hidden connection

knife plates extend into the glulam beams to provide an angled connection.

2 7

1 2 3

4 7

4

5

7

Pre-assembled truss system

6

The four-storey tall pre-assembled truss comprises the following components: 1 Glulam column 2 Glulam beam 3 Steel

angle 4 Glulam cross bracing 5 Dowels 6 Truss below 7 Slotted-in steel plates

Mjøstårnet | 155

1

2

3

4

Construction sequence 1 Depending on its location, the pre-assembled truss may include the glulam brace and beam. The truss is placed and connected to the truss

below starting on the front side of the core. 2 More trusses are placed and the cross bracing is extended as each truss is added. Remaining beams continue to be installed between the trusses. 3 Trusses installed on the side and back of the cores 4 The trusses for the building‘s two short sides are installed last.

Lifting, picking and installation of the prefabricated truss

156 | CASE STUDIES: 9 FRAME SYSTEMS

View of the building from across the lake

foundations and superstructure optimized for the 81 metre height, resisting the increased lateral loads imposed on a taller structure was problematic. The solution was to round the edges of glulam beams for the pergola in order to minimize wind resistance. By this means, an overall height of 85.4 metres was attainable. The exposed glulams used for the pergola are made of preservative-impregnated Scots pine.

CONCLUSION

The successful completion of the Mjøstårnet project further proves the viability of the vertical truss concept pioneered at Treet, to overcome many of the challenges of building tall in wood. These include achieving two-hour fire resistance while allowing the

structure to be exposed to view; the comparative lightness of wood structures and their consequent vulnerability to uplift and lateral drift; and the market acceptance across a variety of sectors, that mass wood structures are as safe as traditional steel and concrete equivalents.

The pre-sale of all the apartments in the building and the immediate popularity of the ‘Wood Hotel’ speak emphatically to this last point. Hotel guests are granted access to the rooftop terrace and most other areas of interest within the hotel. On completion Mjøstårnet became the tallest timber building in the world.

Mjøstårnet | 157

HOHO WIEN Vienna, Austria

[RLP Rüdiger Lainer + Partner] 2019 Year cetus baudevelopment Client Woschitz Group Structural Engineer MMK Mayr-Melnhof/Kirchdorfer Composite Floor Panel Fabricator Hasslacher Norica Timber Glulam and CLT Fabricator Handler Bau GmbH Contractor Commercial/Residential Program

The search for balance between ecology and economy has resulted in a cost-effective and flexible structure that will maximize environmental benefits through a prolonged service life.

196 | CASE STUDIES: 10 HYBRID SYSTEMS

Interior with exposed CLT floor as ceiling finish, concrete ring beam and spruce wall panels

Located in Seestadt Aspern, a new community under construction at the northeast edge of the city of ­Vienna, this 24-storey, 84 metre tall mixed-use project achieves a balance between ecology and economy, confirming the viability of hybrid mass wood and concrete construction even in large urban developments.

In addition to offices, the project includes a hotel, gym, restaurants and apartments.

HoHo, short for Holzhochhaus (German for timber high-rise), is the centrepiece project for the Seepark Quarter, the new business district surrounding the ­underground station that links Seestadt Aspern to the city centre. When all phases are completed, the new community will provide living, working and recre­ ational facilities for approximately 20,000 people.

CONCEPT

HoHo Wien represents the latest phase in the Austrian construction industry’s decade long search for a more environmentally friendly yet cost-effective alternative

to traditional concrete and steel high-rise buildings.

While different in detail, it builds on the principles of simplicity, practicality and speed of erection that were established in LCT One, Austria’s first contemporary Tall Wood building (pp. 166–175) Like LCT One, which was completed in 2010, HoHo Wien is a hybrid wood and concrete structure, comprising a kit of standard prefabricated components.

HoHo Wien also represents a programmatic departure from traditional office design. As the nature of work changes from a highly structured and location-based activity to a more flexible and individualized one, HoHo Wien offers not only a healthy and inspiring environment for workers, but ready access to a broad range of other amenities, through the integration of commercial, recreational and hospitality program elements. The focus on occupant well-being is underscored by the use of exposed timber components throughout the building.

HoHo Wien | 197

Floor panel with pre-installed mechanical services element

Concrete ring beam placed on top of the prefabricated column and wall panels below

HoHo Wien  |  199

ABOUT THE AUTHORS

MICHAEL GREEN

JIM TAGGART

Michael founded his architecture firm MGA | Michael Green Architecture, not for profit school DBR | Design Build Research and research platform TOE | Timber Online Education, to focus on progressive architecture, research, education and innovation. From Vancouver, British Columbia, he and his team work on international projects that are diverse in their scale, building type and location.

Since leaving architectural practice in 1992, Jim has written and lectured extensively on the use of wood in contemporary architecture to audiences throughout North America and across the world. He is also the author of the award-winning books Toward a Culture of Wood Architecture (2011) and The Architecture of ­Engagement (2019).

A Fellow of the Royal Architectural Institute of Canada, Michael is vested in helping build healthier communities through innovative architecture, interiors, landscape and urban design. He is particularly known for his research, leadership and advocacy in promoting the use of wood in the built environment with extensive international talks on the subject, including his 2013 TED talk which has been translated into 31 different languages and viewed over 1.3 million times.

Jim has taught architecture at the British Columbia Institute of Technology in Vancouver since 2004, and has been editor of Sustainable Architecture and Building Magazine (SABMag) since its inception in 2006. He is a Fellow of the Royal Architectural Institute of Canada, Executive Director of the Royal Architectural Institute of Canada Foundation and was the recipient of the 2012 Premier of British Columbia’s ‘Wood Champion’ award.

ANDREW WAUGH

Andrew is a founding director of Waugh Thistleton ­Architects, London. Andrew has led the practice on award-winning schemes from cinemas to synagogues; social housing to offices and was responsible for the design and delivery of Murray Grove, 2009, the project which spearheaded the international movement in tall timber construction, and Bushey Cemetery which was shortlisted for the prestigious Stirling Prize in 2018.

About the Authors | 213

This publication provides a systematic introduction to the tech­ nology and explains typical Tall Wood constructions such as panel systems, frame and hybrid systems. An international selection of 18 best-practice case studies is documented in detail with many specially prepared construction drawings, demonstrating the range of the technology.

Both authors are experienced specialists for timber construction: Michael Green (MGA | Michael Green Architecture), Vancouver, and Director of the non-for-profit school DBR | Design Build Research, is a researcher and practitioner in the field of timber structures. His 2013 TED talk, viewed over 1.3 million times, made a large audience aware of Tall Wood buildings.

Jim Taggart, Vancouver, is an architect, publicist and editor of Sustainable Architecture and Building Magazine. He has taught architecture at the British Columbia Institute of Technology in Vancouver since 2004. He is also the author of the awardwinning books Toward a Culture of Wood Architecture (2004) and The Architecture of Engagement (2019).

TALL WOOD BUILDINGS

Over the last decade, Tall Wood buildings have been at the forefront of innovative building practice in urban contexts. In many cities around the globe, these timber high-rises have emerged as a new urban element. Mass timber buildings of up to 20 storeys and a height of 85 meters have been built, are under construction or being considered. This dynamic shift has been enabled by the emergence of new engineered wood products, prefabrication and more flexibility in fire regulations. The low carbon dioxide footprint of wood – often regionally sourced – make it a responsible choice for today’s buildings.

MICHAEL GREEN JIM TAGGART

www.birkhauser.com

MICHAEL GREEN JIM TAGGART

TALL WOOD BUILDINGS DESIGN, CONSTRUCTION AND PERFORMANCE

SECOND AND EXPANDED EDITION