“TallWood Project” Testing Confirms Mass Timber’s Impressive Seismic Resilience

After three months of testing and more than 100 simulated earthquakes, the 10-story “Tallwood Project” building has demonstrated the impressive seismic resilience of mass timber buildings, according to a review of the results by temblor (2-14-24), a catastrophe modeling company specializing in seismic hazard and risk assessment.

As building codes change to include multistory mass timber structures, people living in seismically active regions may be wondering how these new mass timber structures will hold up in an earthquake event. Now they have an answer.

Background

The TallWood Project building was designed and constructed by a team led by Colorado School of Mines associate professor Shiling Pei and dubbed the Natural Hazards Engineering Research Infrastructure (NHERI) TallWood Project. The National Science Foundation-funded project is managed by the University of California, San Diego (UCSD) where the tower was built. At 112 feet (34 meters) in height, the mass timber tower is the tallest full-scale building structure to ever be tested on a shake table.

The UCSD-operated shake table is the largest outdoor earthquake simulator in the world. Thanks to a recent upgrade, it can carry 4.5-million-pound structures through realistic, three-dimensional earthquake simulations with six ground motion components. “Basically, earthquakes on demand,” Pei told temblor.

This allowed Pei and his team to test their design through a variety of simulated earthquakes equivalent to between magnitude 4 and magnitude 8 events. They started slowly, testing quakes smaller than those the building was designed to withstand based on design codes. They ramped up the magnitude until reaching several ground motions equivalent to earthquakes with a 2,500-year return period, a monster seen “every three to five centuries,” Pei says. In each case, more than 750 sensors interspersed throughout the building captured its movement.

The tower was built to withstand Seattle’s earthquake hazards. It features four mass timber rocking walls. Rocking walls, which are a type of self-centering design, are constructed to prevent significant damage during a quake. Each 10-foot-wide panel spans the height of the tower and is anchored to the shake table with steel rods. These rods control the motion of the walls, allowing them to lift on one edge and compress on the other while rocking. When the shaking stops, the rods bring the wall’s edge back to being flush with the shake table—equivalent to the foundation. Thus, the building returns to its original vertical position.

Results

Although self-centering designs are not new, incorporating rocking walls into mass timber structures is fairly novel, according to temblor. In 2017, Pei led a previous project that tested rocking walls in a wooden two-story building on the same shake table. However, in addition to being the tallest wooden building ever tested on a shake table, TallWood is the tallest to test such walls. “Theoretically you can always say ‘I think that idea will work,’ but this is the first time to actually see it work in [a] 10-story wood building,” Pei told temblor.

A second round of testing at UCSD in collaboration with the Japanese company Sumitomo Forestry Co., Ltd. saw the same results with regard to seismic damage despite slight structural modifications to accommodate Japanese building codes. Those codes require stiffer walls compared to codes in the United States, Pei explains. Ultimately, he says the lateral rocking wall system proved to be “adaptive to different code requirements.”