Better buildings
October 18, 2021

Is mass timber a good choice for seismic zones?

For some, it may be terrifying to think that we inhabit a sphere orbiting the Sun, whose core has temperatures of up to 6,000°C and all human activities are located on the Earth’s crust, the smallest layer in thickness, in the so-called tectonic plates. These plates float on the mantle, more precisely in the asthenosphere, and sometimes collide, causing earthquakes.

Brock Commons Tallwood House construction | Photo credit: KK Law

By Eduardo Souza, ArchDaily

As we can see in this interactive map, earthquakes are much more frequent than we imagine, with dozens occurring daily around the world, many of them unnoticed. But some are extremely potent, and when they occur near urban areas, they are one of the most destructive forces on Earth, causing death and damage to the built environment.

With the advancement of research, tests, and experiments in engineering, countries, and regions with tectonic activities already have the knowledge to reduce the danger of death and damage caused by these events. Some solutions and materials work better in the event of an earthquake. Wood is one of them.

An earthquake emits shock waves at short, rapid intervals, like an extremely severe horizontal charge. Buildings generally support vertical loads well (both dead loads such as the weight of the structural materials, and live loads such as building occupants, furniture, and other equipment). In the case of an earthquake, the lateral forces transmitted by the waves of the earthquake make the entire structure vibrate, which can cause anything from superficial damage to the total collapse of the structure.

High degrees of ductility

Wood withstanding lateral loads

In regions where there is seismic activity, flexible foundation systems, counterweights, and even pendulums are used in tall buildings to avoid or counterbalance the structure as it sways. But in addition to structural reinforcements, the materials that make up the building can play a key role. Wood as a structural material works particularly well in the case of earthquakes, as wood lateral force resisting systems tend to have high degrees of ductility. This means that it is a material that supports a great deal of deformation until the moment of its fracture. That is, it bends before breaking. Just think about the behavior of a tree in a windstorm. This is possible because wood is composed of long, thin, strong cells and the elongated shape of the cell walls gives the wood its high strength parallel to the grain. Wood products can withstand very high loads, particularly when compression and tension forces are exerted parallel to the wood fibres.

Bayview Elementary School seismic replacement | Photo credit: Wade Comer Photography

Mass timber erection of the Bayview Elementary School
Reducing seismic forces

Wood's lightweight advantage

Another positive trait of wood in these situations is that it is a lightweight material. The less mass the building has, the less inertial force will be created with seismic waves. Cristiano Loss, assistant professor of wood engineering at The University of British Columbia, specializes in the resilience of high-performance wood-based systems and structures against earthquakes. Involved in experimental testing of wood assemblies, he points out the inherent benefits of such systems. “One of the things that makes wood stronger by far is its lighter weight. You might think this is a downside, but it’s actually a big advantage,” he explains. “Wood is five times lighter than concrete, considerably reducing the seismic forces in a building.”

wək̓ʷan̓əs tə syaqʷəm Elementary School seismic replacement | Photo credit: Bright Photography

sir matthew begbie elementary construction dec3 2020 photos 003 credit bright photography courtesy