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The Smile

The Smile showcased the extraordinary qualities of American tulipwood and superb design expertise and creativity of its makers and Arup engineers. With a concept inspired by Architect Alison Brooks, this was the first ever mega tube made of timber that you can inhabit and explore; and the most ambitious structure ever made of CLT.


Project Feature
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Design Process
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This project set out to test American tulipwood CLT and showcase it in a series of construction products. Exploiting the properties of tulipwood CLT, Architect Alison Brooks came up with the concept of a beam that curves up at both ends. The CLT tube is an inherently strong shape, in the same way that a steel tube is. The curve means that it cantilevers from, effectively, a single point in the centre.

Although she has worked with Glulam, Brooks has never had the opportunity to work with CLT before – she has tried to specify it but because for example of acoustic constraints it has never been possible to use it without a great number of additional layers.’ ‘Tulipwood itself is not heavy which is helpful; and it has character and a tight grain’, Brooks says.

Andrew Lawrence, Arup’s global timber specialist sees great potential for tulipwood CLT. ‘The reason that timber construction has really taken off, in addition to the sustainability argument, is down to three factors,’ Lawrence says. These are CNC fabrication, the invention of CLT and the introduction of cheap modern self-tapping screws. 

‘The thing about this project,’ he says,’is that it actually combines all three innovations. It is all CLT. Nearly all the connections are modern self-tapping screws, and it completely relies on CNC manufacture.’ Softwood will always be the workhorse of timber construction, but where improved strength and appearance are needed, then he believes hardwood CLT is the answer.

Environmental Profile
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Andrew Lawrence, Arup’s global timber specialist says ‘This is by far the most complex CLT structure that has ever been made. It was a massive challenge in terms of scale and engineering as well as a demonstration of just how exciting and beautiful a building using CLT can be’.

Not only does it have a double cantilever, but the entrance door in the centre of the structure is placed exactly where the stresses are highest. Solving these challenges has useful lessons not only for this structure but also for all future CLT buildings. 

‘Although it is a sculpture,’ he says, ‘you are effectively looking at a 20m cantilever that is like the core we use to stabilise a building. The weight of 60 people at one end of the cantilever is equivalent to the wind load on a five-storey building. Nobody has done a core that slender in wood.’ 

One of the first challenges for Lawrence was determining the properties of the American tulipwood that the project is using. The strength of the CLT is derived from testing undertaken on 100 full size planks of tulipwood 15 years ago. 

The design had to take some very demanding circumstances into account. The shape and the loadings mean that it is in tension at the top over the door and in compression through the floor under the door.  In addition to the position of the door, there was the way that The Smile sits on its wooden foundation. This is partly buried in the ground, to minimise the visual impact and, for the same reason, is as small as possible, while not allowing it to be so small that the structure could roll over, lifting the foundation which is weighted by the use of steel weights within the wooded box. 

Another consideration relates to the behaviour of visitors. The designers had to allow for the fact that all the visitors could be at one end of the structure at one time – another design consideration was that everybody might stand to one side, tending to turn The Smile on its side.

The structure also had to be strong enough to resist ‘lozenging’, the tendency to distort from a square cross section to a rhomboid when the wind blows from one side with a force equivalent to 10 tonnes. Therefore stiff moment connections have been introduced at the roof to wall junction to limit the amount of lozenging. All the connections were achieved with self-tapping screws, about 400 mm long and very carefully positioned. 

Another challenge comes from the sheer size of the elements. CLT lends itself to being made in large pieces and in this case it is essential, as there could not be a join in the centre, where the structure is most highly stressed. 

After all this work and effort, assembly was relatively simple, ‘like a piece of IKEA furniture but on a much larger scale,’ said Lawrence.

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For further press information about AHEC and The Smile please contact: 

Sabine Zetteler / Emily Ward, Zetteler:

ahec [at] zetteler.co.uk

For further information about Alison Brooks Architects please contact: 

Diane Hutchinson / Miriam Mandel, Caro Communications
diane [at] carocommunications.com  
miriam [at] carocommunications.com   
+ 44 (0)20 7713 9388

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The Smile, effectively a beam curving up at both ends, was designed by Alison Brooks Architects and engineered by Arup. It is the first ever mega tube made of timber that you can inhabit and explore; and the most ambitious structure ever made of CLT. Made from American tulipwood, engineered into a pure and efficient structural form, this was an innovative and ground-breaking Landmark project for the London Design Festival 2016: installed in the courtyard of Chelsea College of Art, almost opposite Tate Britain.

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For over 25 years the American Hardwood Export Council (AHEC) has been at the forefront of international wood promotion, successfully building a distinctive and creative brand for U.S. hardwoods. AHEC’s global programme of activities secure a future for American hardwoods by demonstrating the performance and aesthetic potential of these sustainable materials, while providing valuable creative inspiration and technical advice.



Founded in 1996, Alison Brooks Architects has developed an international reputation for delivering design excellence in projects ranging from urban regeneration, master planning, public buildings for the arts, higher education and housing. ABA’s award-winning architecture is born from intensive research into the cultural, social and environmental contexts of each project. This approach enables them to develop authentic, responsive solutions for our buildings and urban schemes, each with a distinct identity. Combining formal invention with rigorous attention to detail, ABA’s buildings have proved to satisfy our client’s expectations and positively impact the urban realm. Alison Brooks Architects is the only UK practice to have won the RIBA’s three most prestigious awards for architecture - the 2008 Stirling Prize for Accordia Cambridge, the Manser Medal and the Stephen Lawrence Prize. ABA numerous national and international awards include the 2012 Architect of the Year and Housing Architect of the Year.



Arup is the creative force at the heart of many of the world’s most prominent projects in the built environment and across industry. From 90 offices in 35 countries 11,000 planners, designers, engineers and consultants deliver innovative projects across the world with creativity and passion.



The London Design Festival is a key constituent of London’s Autumn creative season, alongside London Fashion Week, Frieze Art Fair and the London Film Festival. Established in 2003 its role is to celebrate and promote London as the world’s design capital and gateway to the to the international design community and it has now established a reputation as one of the largest and most exciting design events in the world. 



ZÜBLIN Timber are a single-source provider for the development, production, delivery, and execution of construction systems, from timber construction projects to timber engineering to turnkey project execution.



University  of  the  Arts  London  (UAL)  is  Europe's  largest  university  for  art,  design,  fashion,  communication and the performing arts. It is a federation of six internationally renowned colleges:  Camberwell College of Arts, Central Saint Martins, Chelsea College of Arts, London College of Communication, London College of Fashion and Wimbledon College of Arts. UAL was recently ranked one of the world's top 5 universities for art and design 2016/17 in QS World University Rankings.

Chelsea College of Arts, UAL, is one of the world’s leading art and design institutions specialising in Fine Art, Graphic Design and Interior and Textile Design. Alumni include Turner Prize winning artists Anish Kapoor and Chris Ofili, Oscar winner Steve McQueen and actor Alan Rickman. Chelsea is one of the six Colleges of University of the Arts London (UAL). 



Middle Tennessee Lumber

Blue Ridge Lumber

Robert Coleman Lumber

Beard Hardwoods, Inc

Allegheny Wood Products

The Turman Group

W.M Cramer Lumber Co.

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American tulipwood

Commercially American tulipwood, known domestically as yellow poplar, is one of the most prolific hardwood species from the U.S. hardwood forests and is unique to North America. Forest Inventory Analysis (FIA) data shows U.S. tulipwood makes up 7.7% of total U.S. hardwood growing stock and while 12.8 million m3 are harvested each year, more than 32 million m3 of American tulipwood grows naturally in the hardwood forests during the same period. Tulipwood has less strong grain characteristic than species such as ash and oak and exhibits a marked difference between the sapwood and heartwood. The sapwood is creamy white whereas the heartwood can vary from pale yellow or brown to green and purple in extreme cases. The wood darkens on exposure to light. Tulipwood has extraordinary overall strength properties relative to weight, making it highly suitable for structural applications, such as glue-laminated beams and cross laminated timber (CLT).

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The Smile was to be an urban installation aimed at transforming the way architects and engineers approach timber construction. 

David Venables, AHEC’s European director and initiator of the project, said ‘This project is meant to represent the challenges of a building… American tulipwood is an abundant, lightweight but strong hardwood; and The Smile is the culmination of an effort by AHEC to show that it can have a structural use in buildings’.

While CLT is becoming a widely accepted means of building around the world, it has been done exclusively in softwood so far. In contrast to previous AHEC experiments with hardwood CLT, this installation would be made using a real manufacturing process rather than the hand-crafted approach. AHEC’s vision was to showcase a product that industry can embrace and present as a solution for architects and engineers: whether in public buildings or in lower cost affordable housing.


Design Process




Environmental Profile