This summer, a seven-story, 17,000-square-foot wood-framed condo tower will be placed on the world’s largest earthquake shake plate, in Miki City, Japan, to test the resilience of taller wood buildings under seismic conditions. The NEESWood Capstone tests, as the project is known, will culminate a four-year-long research effort that involves five universities; the governments of the U.S., Canada, and Japan; and several manufacturers. Hawaii’s Maui Homes is the builder.
The goal is to uncover evidence about the safety of higher mid-rise wood structures in seismic areas. The National Science Foundation, which provided a $1.4 million grant for this project, estimates that 75 million Americans live in places at risk from earthquakes. John van der Lindt, a professor of engineering at Colorado State University and the project’s director, thinks the tests could prove the feasibility of using wood for buildings as tall as seven stories.
Wood-framed buildings are going higher in North America, Japan, and especially Europe. California’s codes allow for a Type 3 building constructed from treated wood up to five stories, typically sitting atop a garage or concrete slab. On April 1, British Columbia raised the allowable height of wood-framed buildings to six stories, from four. And Japan just started allowing wood buildings up to five stories, from three.
In late February, tenants and owners started moving into what’s being touted as the world’s tallest wood building, a nine-story apartment tower in London’s East End. The construction of that building—29 units within eight stories over one story of concrete—features layers of cross-laminated panels joined together, Tetris-like, with metal fittings.
The tower’s architect, Andrew Waugh, says his company is planning a 17-story wood building and will experiment with a 25-story structure. That would be unheard of in the U.S., where the International Code Council (ICC) limits wood-framed buildings to four stories or six using “heavy timber,” says Gary Nelson, ICC’s senior staff engineer for architectural and engineering services.
Wood presents challenges, like shrinkage that causes structures to shift in ways that become more exaggerated as buildings get taller. Waugh acknowledges that humidity in many parts of the U.S. limits using wood for higher structures. But neither he nor other experts think existing fire codes in America pose insurmountable obstacles to building taller.
Wood construction has its benefits, too. Waugh says the increased cost of using laminated panels for the London project was offset by the reduction in its construction schedule to 49 weeks from the 72 it would have taken had concrete and steel been used.
A five-year analysis of seismic impact on wood-framed structures, conducted by CalTech and the Consortium of Universities for Research in Earthquake Engineering, found “a history of good performance,” says Kelly Cobeen, who coauthored a book about those findings. But as wood buildings have grown taller in the Western U.S., there haven’t been recent seismic events against which to gauge their performance. Hence the tests in Japan.
On June 23, the Capstone tower will be subjected to shaking that simulates earthquakes projected for every 72 years and 475 years. Then on July 17, its steel-framed first floor will be braced to the shake plate so the wood-framed structure can be tested separately against a seismic occurrence similar to what hit Northridge, Calif., in 1994. Van der Lindt expects the building to sustain “repairable” damages. As for the practicality of wood for buildings higher than six stories, he remains skeptical for many reasons including that “the horizontal diagram would have to transfer an awful lot of shear.”