Tuesday, July 28th, 2009
Civil engineering's David Rosowsky has been a PI on an NSF project that set out to design mid-rise wood structures for high seismic regions. The project came to a conclusion in July when the researchers’ seven-story wood-frame building successfully survived a an earthquake.
In states that border the Gulf of Mexico, residents are experts on what to do when a hurricane hits: board up the windows, pack up priceless belongings, head into the hours of endless traffic and hope for the best.
Unfortunately, there is little individuals can do to prepare for natural disasters that strike with little or no warning.
Earthquakes are among the deadliest and most sudden natural disasters, leaving residents reliant upon their homes’ earthquake safety standards. One researcher at Texas A&M University is working to give residents of mid-rise buildings in earthquake prone areas greater peace of mind.
For the past five years Dr. David Rosowsky, department head and A.P. and Florence Wiley Chair in the Zachry Department of Civil Engineering at Texas A&M, has been one of the principal investigators on the National Science Foundation’s NEESWood Project. Researchers set out to design mid-rise wood structures for high seismic regions. The project came to a conclusion earlier this summer when the researchers’ seven-story wood-frame building successfully survived a maximum credible event ground motion — an earthquake that may be expected to occur on average only once in 2,500 years.
According to Dr. John van de Lindt, lead project investigator and associate professor of civil engineering at Colorado State University, wood-frame structures are currently limited to four stories “due to the lack of understanding of the dynamic response of taller (mid-rise) wood-frame construction, non-structural limitations such as material fire requirements, and potential damage considerations for non-structural finishes.”
The end goal of the project is to be able to increase the maximum height of wood-frame structures and to lessen the damage to low-rise structures due to earthquakes.
The first full-scale test conducted as a part of the NEESWood project was held at University of Buffalo’s Structural Engineering and Earthquake Simulation Lab in 2006. The team constructed a two-story, 1,800 square-foot townhouse and put it through five mock earthquakes on two interconnected piston-powered shake tables. The mock earthquakes increased in magnitude with each test with the last test equaling the strength of San Francisco’s 1906 earthquake, which had magnitude ranging from 7.7 to 8.3.
The project then moved to Miki City, Japan, for its second and final phase, where the NEESWood researchers worked with the Japanese government’s National Research Institute for Earth’s Science and Disaster Prevention. Miki City is home to the world’s largest shake table in the Hyogo Earthquake Engineering Research Center, E-Defense.
“Both the U.S. and Japan already have derived benefits [from the tests] and will continue to derive benefit in the coming years,” Rosowsky said. “It was truly a collaborative project. While the research was conducted and the structure was designed here in the United States, the entire Capstone structure was built and tested in Japan.”
The building that was constructed for testing in phase two was a six-story wood-frame condominium with a seventh story comprised of concrete and steel representing street-level retail shops. It is 14,000 square-feet with 23 residential one- and two-bedroom units for living space.
“The building was designed using a new approach to designing mid-rise wood story structures… a design procedure called direct displacement design,” Rosowsky explained. “The procedure was developed at Texas A&M University as part of the NEESWood project…And the structure was designed so that under different intensity ground motions, different intensity shakings, the displacement of each story would be kept below specified target levels.”
On June 30, two tests were run on the building. In the first test a mock earthquake was simulated representing the magnitude of an earthquake that takes place only once every 72 years. The second test simulated an earthquake that takes place once every 475 years. On July 6, the building went through the same two tests but with the steel-frame components locked down.
On July 14, the building went through its final test — a maximum credible event based on the 1994 Northridge, Calif., earthquake, scaled to 180 percent intensity. The test is believed to represent an earthquake that would occur, on average, once every 2,500 years.
“The good news is that the test was successful. Not only did the building stay together, but it met all of the performance requirements… it met all of the drift expectations. This confirms that we can design and build mid-rise wood frame structures in high seismic regions and that these structures will perform satisfactorily (as designed).”
Though the final test has been successfully completed, the researchers still have a lot yet to learn from their experiments.
“Now the focus is on taking a look at all the data from the more than 300 sensors on the building, and trying to make sense of all of that information,” Rosowsky said. “The data collected during the test will be used for years to come to validate computer models and further refine seismic design procedures, codes, and standards for engineered wood structures built in seismic regions.”
For more information on the NEESWood Project please visit, http://www.nsf.gov/news/newsmedia/neeswood/index.jsp.
The Zachry Department of Civil Engineering was named in 2005 in honor of the generous and longstanding support of the Zachry Foundation of San Antonio, Texas. The department is one of the largest civil engineering programs in the world and consistently ranks among the top departments in the United States. The undergraduate program is ranked seventh and the graduate program eighth among public institutions in the most recent U.S. News & World Report rankings.
Written by Cassidy Thomas
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