7 minute read
Nature's Invention
John Roycroft
If all the greatest architects, scientists and engineers that ever lived were assembled and tasked with the brief of creating a material with the protean engineering properties and beauty of wood it is highly probable that they would fail. Wood is extremely advanced in terms of its material science and it is the ultimate composite, with a superb mix of structural properties and remarkably complex chemistry. Trees can grow beyond 100m, as tall as a tower, constantly adapting to alter their internal stresses of tension and compression. Trees don’t require any temporary works to achieve their cathedral-like form and they are primarily composed of the element carbon; they are nature’s greatest invention. As stone, bronze, iron, steel and new composites have evolved there has always been an important role for timber. Of all the materials we use there is not one that comes close to timber for versatility and, in its natural form, it is a fundamental part of our ecosystem that keeps the planet healthy. As a structural engineer I am fascinated by how a tree represents the living embodiment of a (well almost always) balanced structural system. Design teams often ask how we can create a tree like structure for a project, but it is difficult to replicate that efficiency and beauty that nature does all on her own. The Body Language of Trees, although a technical guide for tree surgeons, is a fantastically informative read for anyone who seeks to understand how trees work from a structural perspective. Just like a structural engineer, the understanding of tension and compression forces are extremely important for a tree surgeon. Trees are even more complex than building structures and a tree surgeon doesn’t have the luxury of carrying out a Finite Element Model (FEA) before working on a tree. Timber has facilitated the movement of people and goods since prehistoric times through the inventive design of water borne craft. The scale and ingenuity of an 18th century 74-gun ship, or a streamlined tea clipper such as the Cutty Sark are testament to what timber can achieve when used creatively. The scale of these ships is hard to envisage until you consider that each 74-gun ship used up to 3,400 fully matured oak trees, each carefully selected and hand processed - without BIM or complex analysis! Slow growing oak trees are clearly not a sustainable source when one considers the impact of harvesting thousands of mature trees for a single ship. It is only in the last 60 years that large scale timber composite components such as glulam beams, similar in scale to those utilised in ship building, have become more viable for construction purposes. Engineering history often overlooks Brunel’s timber viaducts in Cornwall and his laminated timber bridge over the River Avon in Bath. He also led the development of prefabricated timber hospitals that were used in the Crimean War at Renkioi. Brunel was adept at using materials where they were most suited; he understood that every material has specific properties and advantages and when used in combination can transform a system of components. A long bow is one of the finest examples of this, and the adaptability of wood. Different types of wood combine beautifully within a yew tree to work to their full potential – the heartwood takes care of compression and the sap wood where tension exists. Among heartwood’s unique properties is a resistance to rot: if timber is to be used externally on a building could it be argued that heartwood is a more sustainable choice than impregnating with preservative?
The timber gridshell roof for the National Football Centre was designed to accommodate the trajectory of David Seaman’s goal kick
Laminated timber used to create the 'egg' at Edinburgh Napier University
Timber has featured in many of our projects, such as the National Football Centre at Burton-on-Trent in Staffordshire. The design included a full size football pitch completely covered with a timber gridshell. The column free structure was 74m x 114m and the curve of the roof designed to accommodate the parabolic path of a goal kick by then England goalkeeper David Seaman. We were tantalisingly close to seeing this progressive vision achieved; foundations were constructed before the project was sadly halted and emphasis moved to a new Wembley. At Edinburgh Napier University we designed an auditorium known fondly as the ‘egg’. Here, engineers and architects worked collaboratively to realise the development of laminated timber lumber (LVL) beam sections, using our industry leading CAD modelling expertise and a prefabrication methodology.
With the advantage of low embodied energy, we began to explore the use of timber as a replacement for steel and concrete typically used for the structural frame. Wellington Academy in Wiltshire demonstrated that timber was economic and cost neutral if designed intelligently. The timber structure of columns and beams remains one of my personal favourites. We also designed the boarding houses employing hybrid construction – using cross laminated timber panels, glulam beams and occasional steel beams for long spans. Hybrid structures are a logical way to unlock the potential of timber and some offer glue-laminated timber beams where glass fibre strands are embedded within the glue interlayers. At the multi-award winning Enterprise Centre for the University of East Anglia we used local knowledge, skills and materials, helping to source local timber from Thetford forest that would typically have been sold for fencing posts. We continue to explore environmentally progressive ways of using timber. Our patented design for the zero-carbon Gap House is entirely constructed from prefabricated LVL for rapid onsite assembly of beautiful and affordable new homes. At 80 Atlantic in Toronto, Quadrangle has designed a new workplace with a ‘beam and post’ timber frame, a wonderful example of how to design a sustainable timber frame building with low embodied energy. Canadians use wood with real expertise and innovation; the proximity of 347 million hectares of forest (9% of the world’s forest) is a huge resource, therefore timber is viewed differently by the construction industry. The Richmond Olympic Oval is another great example of using timber in a hybrid form, along with material cut down due to disease; a classic case study of how to unlock timber in a sustainable and creative way. Progressive use of timber in construction during the last 60 years has much to do with using adhesives to create larger structural (composite) components from smaller timber elements from managed forests of faster growing trees. The production of adhesive and how it impacts on the environment needs further consideration and research as its method of manufacture is proving to be the weak link. It is worth noting that while adhesives offer a very effective way of joining timber elements, other methods such as mechanical fixings offer better legacy reuse as elements can be dismantled, although this may be at the expense of material given that mechanical joints are generally less efficient than adhesive. As we need to build higher, timber undoubtedly offers a sustainable solution. Brunel’s ability to utilise materials that work best for each unique situation is just as relevant today. Timber has been used throughout human history, often as a part of a system of components. Early biplanes such as the Sopwith Camel wouldn’t have worked without tensile steel wires; similarly tall buildings need to be considered carefully using a combination of materials to achieve a harmonious and efficient structure; for example at 80 Atlantic the lift cores are reinforced concrete. As cities become increasingly dense it is exciting to imagine a utopian version of Blade Runner where timber towers reach for the sky like a tree breaking through the canopy of a dense forest. We must all work together to challenge conventional thinking on timber and work towards a legacy of low embodied carbon. By emulating the beauty, structural efficiency and positive carbon impact of a 100m tall Redwood, steel and concrete could be consigned to history as the materials of an energy hungry past.
John Roycroft's sketch compares the impressive structural strength of wood
Is it possible to build with timber without a single mechanical connector or adhesive? I urge you all to find a copy of The Art of Japanese Joinery by Kiyosi Seike to learn how craftsmanship, skill and natural materials used with ingenuity can achieve anything. The tools at our disposal, from analysis of structural systems through to robotic production of shapes, are only progressive if we think big, work collaboratively and look to the future - with a respectful nod to the past.
80 Atlantic, Toronto; the first timber framed six storey workplace in the city for over one hundred years
Gap House; prefabricated LVL, flat-packed affordable homes
Continuing the regeneration of Liberty Village
