Wood buildings withstand earthquakes
Wood structures can withstand earthquakes, wind and fire. In the aftermath of an unfortunate disaster, wood is a versatile and resilient building material well-suited to repairing and rebuilding structures.
Wood’s proven track record of seismic performance
Wood’s natural elasticity, strength and lighter weight give it an advantage during an earthquake. The natural ability for wood buildings to flex and return to their original shape (external link) in the event of an earthquake has made them a popular choice for centuries in regions prone to seismic activity. In some instances, historic centuries-old wooden buildings have remained nearly intact after strong earthquakes, while modern reinforced concrete buildings have endured significant damage, or even collapse.
Following earthquakes in Asia, reports indicate that wood structures best maintained their structural integrity and contributed least to injury and loss of life. And recent testing is showing that mid-rise light-frame wooden buildings up to six stories can endure a 7.5 magnitude seismic test with little damage.
Brock Commons Tallwood House | Photo credit: KK Law
Wood’s lightweight advantage
Damaging forces in an earthquake are proportional to a structure’s weight. Wood is substantially lighter than other building materials, giving it an advantage when paired with good seismic design. The fact that wood buildings tend to have numerous nail- or other metal-connections means they have more pathways to dissipate the load (something known as load paths), so there is less chance the structure will collapse should some fail. This is what is referred to as ductility—a building’s ability to undergo large deformations without failing.
What is ductility and how does it boost wood’s resilience?
Ductility is the ability of a material to be deformed without fracture. A building with more ductility can flex and resist collapse. The numerous nails and other connections commonly used in wood construction gives the building more ductility. Many connections mean more load paths to dissipate the forces of an earthquake or high-wind event. Ductility boosts wood building’s resilience.
UBC Forest Sciences Centre | Photo credit: Don Erhardt
Designing for resilience in mass timber and taller wood structures
Tall wood hybrid structures meet, and in some cases, exceed the seismic performance of comparable steel and concrete buildings. Research shows with the right design, wood-steel composite buildings can achieve sufficient stiffness, strength and ductility to resist strong winds and earthquakes. In the case of Brock Commons Tallwood House, the hybrid mass timber structure is significantly lighter than a comparably sized concrete structure. This lighter structure reduces resistance to swaying and uplifting forces during an earthquake, while allowing the building to flex. The building’s concrete core serves as a counterbalance, dissipating seismic forces and minimizing damage to the structure (PDF).
When it comes to high-rise wood construction something called a rocking wall—made from cross-laminated timber (CLT) and designed with post-tensioned cables—can deliver resilient seismic performance.
With this design, the building’s core rocks and then re–centres itself in the event of an earthquake while inflicting no damage to the primary structure. Such an approach to tall timber seismic design goes beyond basic life safety—avoiding the need to tear the building down after an earthquake and making it more easily repaired.
Wood buildings perform in high winds
Strong winds have an inevitable impact on buildings. Wood buildings can withstand substantial loads for short periods, often characteristic of gusty winds. Light-frame construction combined with numerous fasteners and connectors provides multiple and often redundant load paths that can help reduce the impact of high winds. When structural panels such as plywood or oriented strand board (OSB) are fastened to lumber framing, they form some of the most solid and stable roof, floor and wall systems available (external link).
When it comes to taller timber buildings, research is demonstrating that a timber composite system can enhance safety and is a viable option to improve wind resistance (external link). A number of things can be done to boost their resilience in the face of high winds and uplift forces. Examples include steel anchor rods, lateral storey-height trusses, the selective use of precast concrete floors and the use of mass timber panels anchored to the concrete foundation.
RockRidge Canyon Clubhouse | Photo credit: Bob Matheson, courtesy of HDR Architecture Associates Inc.
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