Three-story structure slammed in magnitude 8 earthquake on shake table

SAN DIEGO—Engineering researchers are subjecting a three-story structure resembling a parking garage to a sequence of earthquake "shake test" jolts as powerful as magnitude 8.0 as part of a series of seismic tests to help improve building codes across the nation.

The 1 million-pound precast concrete structure has the largest footprint of any structure ever tested on a shake table in the United States; the shaking of the structure continued through May with the most violent shakes occurring in June. The increasing intensity of the seismic shaking will duplicate ground motions measured in actual earthquakes and adapted specific conditions in Knoxville, Tenn.; Seattle; and Northridge, Calif. Engineers are testing the seismic response of precast concrete floor systems that are used in parking garages, college dormitories, hotels, stadiums, prisons, and increasingly in office buildings.

"This is a landmark test that will enable a very fast and economically advantageous high-technology construction method to be used in seismically active regions of the United States," said Gilbert A. Hegemier, director of UC San Diego’s Powell Structural Research Laboratories, and professor and chair of the Jacobs School of Engineering’s Department of Structural Engineering.

The seismic tests of the one-half-scale structure involve a collaboration among UC San Diego, the University of Arizona, and Lehigh University. The $2.3 million project is being funded by the Precast/Prestressed Concrete Institute and its member companies and organizations, the National Science Foundation, the Charles Pankow Foundation, and the Network for Earthquake Engineering Simulation (NEES).

The goal of the project is to design a building by 2012 that can withstand a major earthquake. In the past, due in part to lack of industry knowledge, individual precast elements pulled apart, much like what happened with the collapse of the nine parking garages during the Northridge Earthquake in Los Angeles in 1994. Since that quake occurred in the early morning, one only one person died. However, experts say the death toll could have been much higher. The other problem is the seismic code for these types of precast buildings is 20 years old. The Precast/Prestressed Concrete Institute recently launched a competition to design better floors for such buildings.