Researchers at Colorado State University and Simpson Strong-Tie say a recent earthquake shake table test near Kobe, Japan, proves that mid-rise wood-frame buildings can be built to withstand major earthquakes and other natural disasters.
More importantly, the engineers say this successful demonstration could lead to code changes permitting more of these types of buildings, which are less expensive to construct than steel or concrete.
"The testing thus far has shown that performance-based design for light-frame wood structures works,” says Steve Pryor, structural engineer for Simpson Strong-Tie in Pleasanton, Calif. “This will allow the engineering and building community to provide safer, better performing buildings in the most cost-effective manner."
John van de Lindt, principal investigator on the test and civil engineering professor at Colorado State University in Fort Collins, says a detailed analysis of the data won’t be available for weeks, but say “scientists are pleased with the initial results.”
The July 14 test was designed to investigate the performance of new design and construction methods for mid-rise, wood-frame buildings in earthquake-prone areas. It also seeks to find ways improve these types of structures. The series of seismic tests, known as the NEESWood Capstone tests, is a collaboration between Colorado State University, Simpson Strong-Tie, and researchers at E-Defense in Japan.
Billed as the world's largest “shake table test," it simulated the ground motion of a 2,500-year earthquake event on a seven-story, 40-foot by 60-foot condominium tower with 23 one- and two-bedroom living units. The shake table, which measures approximately 65 feet by 49 feet and can support building experiments weighing up to 2.5 million pounds, weighs about 2 million pounds. The 40-second test was the equivalent of a 7.5 magnitude earthquake.
“Early results of the testing this summer show that the building performed so well and had so little damage that it validated the design philosophy developed by Colorado State, other universities in the National Science Foundation’s Network for Earthquake Engineering Simulation and our industry collaborators,” van de Lindt says.
The earthquake test is an important event, not so much for being the largest of its kind, but because of the implications for builders and developers in the United States. According to the researchers, the U.S. building industry rarely permits wood-frame buildings in excess of five stories in earthquake-prone areas. The data gathered from this test could increase the height of these buildings and influence the design of future wood-frame construction.
As evidence, the researchers point out that the government of British Columbia in Canada is particularly interested in the results of the test after passing a new law April 1 that increases the height of wood-frame structures from four to six stories.
“In certain areas [of the United States], we’re already seeing six-story plus buildings that are light-framed wood over concrete or steel,” Pryor says. “Properly designed, seismic issues could be conquered and more of these buildings could be built.”
Such a move would be a boon to the construction industry, van de Lindt says. “[Wood-frame] is less expensive,” perhaps by 30%, depending on where you’re building and the type of building,” he says. “There is also the speed of construction, and it’s more sustainable and green.”
Nigel Maynard is senior editor, products, at BUILDER magazine
Click here to view videos (interior and exterior) of the shake test.
For more information on this project, read Ted Cushman's recent blog entry.