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NBC’s “Dateline” rocks the house with simulated 8.0 quake
CEE professor Khalid Mosalam designed and conducted a dramatic visual experiment commissioned by NBC-TV and broadcast on the network’s “Dateline” news program to demonstrate how a pre-code San Francisco home would fare in an 8.0 earthquake.
The program, which aired last May 21, showed footage of the earthquake simulator at Berkeley’s Earthquake Engineering Research Center in Richmond shaking a replica of a Sunset district home. The family that occupies the actual dwelling was shown viewing live video of the test as chandeliers were sent spinning and room furnishings came crashing to the floor. Mosalam appeared to explain the experiment and what it revealed about “soft-story” structures, the term used to describe the first story of two-story houses built over a garage.
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8.0 earthquake simulated on the shake table at Berkeley’s Earthquake Simulator Lab was featured on NBC-TV’s “Dateline” in May. Following the tests, the replica of a pre-code “soft-story” San Francisco home sustained structural damage, and unsecured furnishings on the second story came crashing to the floor.
PHOTOS COURTESY KHALID MOSALAM
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In covering the anniversary of the 1906 quake, NBC wanted a story that would further earthquake research and education. Working with Mosalam and his graduate students, with input from several practicing engineers in the Bay Area, they devised the tests to demonstrate how a pre-code structure would behave in a strong quake. The soft-story structure—typical of homes built in 1930s and ’40s San Francisco—is particularly vulnerable to earthquake damage because of the garage on the first floor. The tests were conducted on the 20' x 20' shake table at Berkeley’s Earthquake Simulator Lab, which can simulate seismic activity and its effect on structures up to 40 feet tall and weighing up to 60 tons.
“My goal was mainly to understand how houses built over a garage behave up to their point of collapse,” Mosalam said. “Ultimately, I would like to come up with affordable retrofit systems for these residential structures.” The garage door retrofit system, although still only in its infancy, would provide homeowners with an inexpensive system that they could install themselves to strengthen a weak first story.
Mosalam ran two tests to demonstrate how furnishings would behave when secured, then unsecured, during a 52-second quake measuring approximately 8.0 on the Richter scale. During these two tests, the house was strengthened to ensure that it remained standing. A third test eliminated the strengthening scheme to demonstrate the effects of the quake on the structure itself.
More than 70 sensors affixed to the house collected data during the tests that Mosalam and his students are now busy analyzing.
“The bidirectional response that combined shaking in two horizontal directions compared with one-directional shaking was very informative and provided us with a better understanding of how such structural systems may twist under strong shaking,” Mosalam said.
Go to the MSNBC website at www.msnbc.msn.com/id/12911952 to see portions of the broadcast.
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