Wood construction offers a huge advantage in terms of sustainability. With its renewability, low required energy, and low carbon footprint, it’s a naturally attractive material. However, some people are not convinced that wood can add to resiliency features.
Here, Mary Uher, regional manager of field services division of APA - The Engineered Wood Association, promotes the use of wood, but says designers need to be aware of the risk factors in the area of construction regardless of what materials they specify.
Uher urges designers to collaborate with all parties involved in the project to pay special attention to every step in the load path. But, by using wood, the project can be resilient and maintain all the sustainability benefits. Jennifer Cover, PE, president and CEO at WoodWorks, Wood Products Council agrees.
“Disasters happen,” Cover says. “It makes sense from an environmental perspective to anticipate adverse situations and minimize, however much that’s possible, the amount of rebuilding that needs to be done. Wood construction provides the resilience expected and needed in today’s cities. Take earthquakes for example, wood projects have a lower mass than projects built with other materials so the forces generated within the structure are less compared to other materials and the ductile and redundant nature of the connections in wood structures allows buildings to accommodate seismic movement without brittle failure.”
Tests highlighted in the U.S. Cross Laminated Timber (CLT) Handbook quantify that feature. CLT-designed buildings that were actually exposed to seismic activity were shown to have the potential to offer more disaster resilience than those built with other heavy construction materials.
Another resilient wood design involves “rocking” mass timber shear walls, which also had impressive results under simulated seismic activity. The tests showed these walls being able to self-correct even after being displaced by 18 inches. This innovative design is being tested in a 12-story Framework project designed by Lever Architecture in Oregon that is expected to break ground soon. Not only will the design be able to self-center after being displaced by earthquake activity, the design also has connectors that can be easily swapped out after a seismic event without major retrofit work.
Another impressive quality of wood is that it can withstand much greater maximum loads for shorter time periods than for longer periods of time, which would occur during high winds or during seismic activity. The repetitive framing with connectors is one factor that helps achieve this strength. The Federal Emergency Management Agency reported that new wood-frame houses built to the 2001 Florida Building Code standards performed well structurally during the 2004 hurricane season, including those that experienced winds of 150 miles per hour in a three-second gust.
As sustainability becomes more of a factor in design, encouraged by code or for capital sourcing, more projects are looking at the option of wood. As it becomes more popular, wood design and construction best practices are being incorporated into the building code.
“The IBC includes many provisions and guidelines for designing buildings to better withstand disasters—and it continues to evolve to improve building performance,” says Cover. “For wood buildings, the code is supported by referenced standards such as the American Wood Council’s National Design Specification for Wood Construction and Special Design Provisions for Wind and Seismic that help people design buildings to meet loadings associated with naturally occurring threats.”
And, although no single building material can provide all the answers to resiliency, wood is finding its place in the discussion.