Good Wood! Using Wood to Transform Multi-Storey ConstructionPosted: October 16, 2016
The Brock Commons building at the University of British Columbia is well on its way to completion in the Fall of 2017. The 18-storey student residence is part of a growing list of tall structures built primarily of wood. A 14-storey building in Bergen Norway is currently the tallest; in 2017 construction starts on a 21-storey building in Amsterdam. A 40-floor condo in Stockholm is on the drawing boards.
Ingrained habits and thinking have placed blinders on both builders and customers as to the massive changes in wood-based materials technologies. This blog has been stunned by the waste and inefficiency of current building practices; as lean practitioners these building projects are a welcome development.
In The Economist’s coverage they wrote:
The five-storey pagoda of the Temple of the Flourishing Law in the Nara prefecture of Japan is one of the world’s oldest wooden buildings. It has withstood wind, rain, fire and earthquakes for 1,400 years. Analysis of the rings in the central pillar supporting the 32-metre structure suggests the wood that it is made from was felled in 594, and construction is thought to have taken place soon after.
In an age of steel and concrete, the pagoda is a reminder of wood’s long history as a construction material. New techniques mean that wood can now be used for much taller buildings.
In recent years there have been big advances in “engineered” wood, such as cross-laminated timber (CLT) made from layers of timber sections glued together with their grains at right angles to one another. In much the same way that aligning carbon-fibre composites creates stronger racing cars, aircraft and golf clubs, CLT imparts greater rigidity and strength to wooden structures.
A recent experiment by Skidmore, Owings & Merrill, a firm of architects, and Oregon State University, shows how strong engineered wood can be. The researchers used CLT in a hybrid form known as concrete-jointed timber. This featured an 11-metre wide CLT floor section with a thin layer of reinforced concrete spread across the surface. Thicker sections of concrete were added where the floor was supported by pillars. It was put into a giant test rig where a powerful hydraulic press pushed with increasing force onto the surface. The researchers wanted to see how the structure moved under load, but kept pressing in order to find its limits. The floor finally began to crack when the load reached a massive 82,000 pounds (37,200 kg), around eight times what it was designed to support.
In general, a large mass of wood, such as a CLT floor, is difficult to burn without a sustained heat source—for the same reason that it is hard to light a camp fire when all you have is logs. Once the outside of the timber chars it can prevent the wood inside from igniting. The big urban fires of the past, such as the Great Fire of London, which occurred 350 years ago this month, were mostly fuelled by smaller sections of timber acting as kindling. Prospective tenants would doubtless need lots of reassurance. But with other fire-resistant layers and modern sprinkler systems, tall wooden buildings can exceed existing fire standards, reckons Benton Johnson, a project leader with Skidmore, Owings & Merrill.
He says the test showed that not only can wood be made strong enough for tall buildings but that “it makes sense to use it”. Although a cubic metre of concrete is cheaper than an equivalent volume of timber, wooden buildings can be built faster. Mr Johnson thinks the appeal of wood, both visually and as a sustainable material, will make it commercially attractive to property developers.
What about wood worm and rot? “If you don’t look after it, steel and concrete will fail just as quickly as timber,” says Michael Ramage, head of the Centre for Natural Material Innovation at the University of Cambridge in Britain.