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World's Largest Earthquake Shake Table Test in Japan

 





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A full-scale, seven-story wood-framed condominium tower not only survived a 7.5 magnitude earthquake, but it escaped with barely a scratch – just minor drywall damage. In July 2009, Simpson Strong-Tie participated in an unprecedented research event to highlight the importance of earthquake-resistant construction around the world.

As the world's largest full-scale test ever attempted, the NEESWood Capstone project was developed to test new design methods for multistory, wood-frame buildings during large seismic events, and ultimately improve the construction and safety of wood buildings in the U.S. The project featured a seven-story, 40- by 60-ft. condominium tower with 23 one- and two-bedroom living units and two retail shops on the ground level. The condo building was subjected to Japan's E-Defense (Earth-Defense) shake table, which simulates the ground motions of an earthquake.

Located just north of Kobe in Miki City, Japan, the E-Defense shake table measures approximately 65 by 49 ft. and can support building experiments weighing up to 2.5 million pounds. The project's condominium tower weighed nearly a million pounds and was outfitted with Simpson Strong-Tie products, including steel special moment frames on the first floor, and 63 Anchor Tiedown Systems (ATS) and structural connectors to secure the six-story wood structure.

Project lead Colorado State University and technical collaborator Simpson Strong-Tie used the shake table to recreate a series of earthquakes based on the 1994 Northridge, California, earthquake – a 6.7 magnitude quake. The special moment frame was tested to a 60% Northridge record and a 140% Northridge record. The frames were then braced to isolate the six-story wood structure for the remaining three tests. During the third and fourth tests, the six-story wood building was subjected to 60% and 120%, respectively, of the Northridge quake.

In the final and strongest test, the seismic intensity was increased to 180% of the Northridge earthquake, roughly a 7.5 magnitude earthquake.

Initial Test Results
Remarkably, the building performed better than expected. "We saw minor drywall cracks from window and door corners," said Steve Pryor, S.E., Simpson Strong-Tie lead researcher for the project. "After the first four tests, the fifth and largest test (180% Northridge) showed only a very slight increase in the amount of drywall cracking and there was very minimal nail withdrawal. The vibrational frequency of the building also did not change, which indicates that the fundamental structural system in the building suffered no appreciable damage."

Unlike traditional building design, the Capstone building was built with Performance-Based Design. This design method goes above the code minimum to help prevent structural and nonstructural damage caused by an earthquake. The Capstone building demonstrated that with a little more design consideration up front and a few more dollars in construction, it is possible to save structures, potentially saving billions of dollars after a major seismic event.

Project Collaborators
The NEESWood Capstone Tests are the culmination of five universities and a four-year $1.4 million grant from the National Science Foundation to develop a new design approach for taller wood-frame buildings in urban, earthquake-prone areas. Co-investigators funded by the NSF NEESWood grant include CSU, Texas A&M University, SUNY-Buffalo, RPI and University of Delaware. Simpson Strong-Tie served as the lead technical collaborator and provided the structural hardware for the building. Honolulu-based Maui Homes USA was the project contractor and was supported by the U.S. Forest Products Laboratory, FPInnovations Forintek Division in Canada and Japan's National Institute for Earth Science and Disaster Prevention. Additional project contributors included the Provincial Government of British Columbia, the American Forest and Paper Association, Stanley Bostitch, Strocal, Inc. and several other building suppliers.

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