Wood science leads to better construction

Materials World magazine
,
2 Mar 2016

Peter Wilson looks at how technical analysis of timber can lead to improved construction and engineering techniques.

Timber research has led to some of the most innovative product developments to be found in the construction industry in recent years, with new ideas and manufacturing opportunities rapidly transferring themselves between countries around the globe and stimulating previously unconsidered areas of investigation. But using the term ‘timber research’ is perhaps too general for a field that embraces disciplines as distinct as silviculture, wood science and timber modification, product development, construction technology as well as more recent thinking about the nano-technological possibilities inherent in the molecular structure of the trees grown in different parts of the world and their very different characteristics.

Certainly, we are familiar with the travels and researches of the likes of David Douglas who brought seeds of unusual species from North America to Europe where, on replanting, they grew to form the fir trees that now carry his name in the UK and France – where its proponents have lobbied to trademark the locally grown material as ‘le Douglas’. Similarly, the Sitka spruce introduced from the Pacific west coast of Canada to the UK after the First World War as a relatively disease-resistant, fast growing, straight softwood replacement for the massive volumes of timber that had been felled to provide material for trench linings and pit props during the fighting is now our predominant production species in the UK. We have copious volumes of larch too, with the European and Japanese versions dominating in different parts of the UK. 

But just as we have imported the seeds of many different species, so too have we immigrated a range of diseases affecting not only timber quality but also the very existence of a several important species. Dutch elm disease virtually eradicated one of the finest trees in the UK landscape, while today ash, oak, larch and Scots pine are all under threat from pathogens. The potentially catastrophic impact of this on our forest sector has opened up whole new areas of research, not only into ways of combating the respective viruses involved, but also into identifying new uses for the felled timber that maintain some, if not all, of the raw material’s value rather than simply seeing it burned as a means of eradicating the infections.

Finding answers

While we continue to search for solutions, an international example of original thinking about what is possible can be found in Canada's Richmond Oval, the ice skating arena built for the Winter Olympic Games in Vancouver in 2010. The mayor of Richmond wished the building to highlight the area’s landscape and economy to the world, which, in British Columbia, means trees. A significant problem in realising this ambition, however, was the fact that the region’s pine trees were blighted with a beetle infection that was ravaging the entire resource. Engineer’s Paul Fast and Gerry Epp (Fast+Epp) developed an ingenious response to this challenge, the result being glulam beams that span the 90-metre arena with intermediate ‘wood wave’ beams manufactured from standard sawmill sections to provide astonishing acoustic control to a building with hard, reflective surfaces. The overall result is a quiet and, paradoxically, warm-feeling space that uses wood from 6,000 diseased trees, with the added benefit of a huge volume of atmospheric carbon dioxide being locked up in the material. In this example, understanding the properties of the native species, the nature of the disease and its possible effect on the structural capacity of the timber (it remained structurally sound) allowed the engineers to analyse, develop and test their proposition at full size and in doing so to fulfil a brief that required them to demonstrate the potential to construct large scale, modern buildings from the local, albeit infected, resource.

The potential to engineer our way out of problems brought by disease or to find new and better ways to raise the value and the construction potential of low-quality timber has, in recent years, brought different areas of research into closer proximity, with innovative new solutions continuing to emerge as a result. Where once different disciplines worked in glorious isolation with research results being disseminated primarily to consenting adults in the same field, there is nowadays convincing evidence of creative crossover. The way in which wood lamination has developed over the past 30 years is a good example of this – searching for ways to deal with the twin challenges of low quality timber and overproduction in the Swiss timber industry in the late 1980s, Professor Julius Natterer conceived the idea of a nailed solid wood system in which standard planks were nailed together in stacks to produce solid floor and wall panels.

This low technology solution to a forest sector problem led on to a dowelled option in which hardwood rods are inserted into holes continuously drilled through stacks of softwood, with the two different timbers tightly connecting the panels as the differing moisture content of each reaches equilibrium. The concept is not much different to that of traditional timber frame structures in which timber pegs tighten joints as the green (unkilned) structural timber slowly dries out.

Subsequent innovation based in both wood science and in the ongoing improvements in precision manufacturing machinery has led to the idea of ‘wood welding’, in which wooden rods are rotationally inserted at high speed into the receiving holes in the stacked planks, resulting in the lignins in both species melding to form extremely tight, natural (i.e. non-glued) bonds. This nascent technology has attracted widespread interest, with a range of wood science and engineering specialists in universities and research centres across Europe and north America now actively looking to work together with manufacturers to improve and test the process towards commercial production.

New thinking, new techniques

The big area of technical development in recent years has, however, been in glued laminated timber systems, with cross laminated timber emerging in our modern age of environmental concern and drive for low energy use as a significant driver of new thinking in building design and construction. This manifests itself in new thinking about the thermal performance of wood and the ways in which this might be optimised in hybrid construction. Similarly, the hygroscopic nature of wood is being used to deliver better internal air quality in buildings through the surface exposure of solid panels, rather than concealing them beneath gypsum wall linings. 

At the other extreme, much analysis, development and testing is being invested in ultra lightweight timber solutions, the objective being not to focus on the carbon storage benefits of wood but instead to explore ways in which microscopically thin veneers can be laminated to form credit card-thin panels that, in combination, can be fabricated into immensely strong structures. Such ideas would not have been feasible 25 years ago, but advanced computer hardware and form-finding software systems now allow engineers to conceive and manufacture new building solutions founded upon better understanding of the molecular structure of wood and the characteristics and performance qualities of different species, individually and in conjunction.

An example of this is the ‘Voussoir Cloud’, developed by the San Francisco office of structural engineer Buro Happold in collaboration with Iwamoto and Scott Architecture and assisted by students from the Southern California Institute of Architecture (SCI-Arc), USA, where the first manifestation of this experimental structural system was exhibited. The name itself is intentionally challenging, voussoirs being heavy wedge-shaped masonry blocks that bear on each other to form arches – in this version, the voussoirs, or ‘petals’, are made from paper-thin wood laminates folded along curved seams to provide both strength and geometric form. The folds give the petals a wedge shape, enabling them to act in compression. The ‘Cloud’ refers to the very evident lightness of form and the ethereal glow from the light passing through the wood laminate.

Experimental structures such as this are transformative and ably demonstrate some of the ways in which traditional perceptions of how we build with wood are being radically altered in response to 21st century environmental imperatives and available natural resources. Research of this sort can be lengthy and expensive and much of the funding these days is catalysed by European Union grants designed to encourage academic establishments and research institutes to work together with SMEs in new cross-disciplinary networks aimed at identifying and testing new solutions. Knowledge transfer is a vital part of this process and is especially important for researchers and manufacturers in the UK where investment in forest and wood science research as well as in processing technology is severely constrained. Yet the forest and timber processing sector as well as the wood construction industry has a huge financial value – in Scotland alone a recent assessment of the forest sector’s annual worth to the national economy was put at £1bln, with potential growth in the private sector suggesting this could be doubled within the next few years. As we move away from materials derived from petrochemical sources to more bio-based possibilities, can we afford any longer to view wood products as really only suited to small domestic construction or can we aim much higher – to the clouds, even? 

Peter Wilson is an architect and managing director of Timber Design Initiatives Ltd. His raison d’etre is to deliver new Europe-wide approaches to education, innovation and demonstration of best practice in the use of wood in architecture design and construction.