Wood has many attractions as a construction material, apart from its aesthetic qualities. A wooden building is about a quarter of the weight of an equivalent reinforced-concrete structure, which means foundations can be smaller. Timber is a sustainable material and a natural “sink” for CO2, as trees lock in carbon from the atmosphere. Tall steel-and-concrete buildings tend to have a large carbon footprint, in part because of the amount of material required to support them. Using wood could reduce their carbon footprint by 60-75%, according to some studies.
There are two main concerns about using wood to build high. The first is whether wood is strong enough. 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 (37,200kg), around eight times what it was designed to support.
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