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Faking Earthquakes

By Heather Holliday I November 22, 2004

The 70-foot-tall, 23,400-pound wind turbine shuddered and swayed as it reacted to the effects of a simulated magnitude 7.3 earthquake. The 40-second simulation, conducted Nov. 15 by the Jacobs School of Engineering at Camp Elliott, was accompanied by an eerie, low-pitched whine.

Video of Press Conference

The fake temblor was caused by the nation's largest outdoor shake table, sized at 25 feet by 40 feet. The table is capable of shaking up to 6 feet per second – allowing researchers to reproduce realistic simulations of earthquakes. The facility, which was designed and built by UCSD faculty and students, can accommodate about 2000 tons, roughly the size of a five-story building, said José Restrepo, a structural engineering professor and co-investigator with the project.

“We’ll be able to reproduce accurately the ground movement that has been recorded before in very strong earthquakes,” said Restrepo. “The intention with this facility is to do landmark experiments on tall complex structures that have never been able to be performed before because of height and capacity limitations.”

Last week's experiment tested how well large wind turbines can withstand forces created during earhquakes.

"Our demonstration is a first step towards understanding how wind turbines are impacted by earthquakes, a question that will become increasingly important as California becomes more reliant on renewable energy sources such as wind energy," Restrepo said. "A significant concern is the resilience of wind turbines to earthquakes because the main wind energy producing regions of California are within close proximity to active earthquake faults."

UCSD structural engineers also will use the shake table to conduct seismic experiments on multi-story buildings, bridge columns and bents, wharfs and piers, and lifeline structures such as electrical sub-stations and satellite towers. The shake table is adjacent to the Soil Foundation-Structure Interaction (SFSI) facility funded by the California Department of Transportation. Taken together, the shake table and SFSI will allow for one-of-a-kind testing of structural systems such as bridge abutments, embankments and foundations.

The demonstration was part of a grand opening for a network of seismic testing laboratories at 15 universities – the National Science Foundation’s George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES). The network, which includes University of Colorado at Boulder, Cornell University and Berkeley, Davis and UCLA from the UC system, will implement seismic experiments on buildings, bridges, utility structures and nuclear containment casks.

The grand hope, said Bob Englekirk, chairman of the board of directors for Camp Elliot, is to reduce the loss of life during an earthquake and significantly reduce the amount of damage that is caused. “Wouldn’t it be nice if after an earthquake everybody said, ‘I don’t have to go to Disneyland this week, I’ve had my ride,’” he said.

“The significance of this table from an engineering standpoint is that it allows us to test our analytical procedures,” Englekirk added. “Seventeenth century thinkers would say that our earthquake engineering procedures today fall into the realm of philosophy and not science. This table will allow us to demonstrate that we do know what we are doing when we are predicting seismic behavior.”

Construction of the shake table, located at UCSD's Elliott campus at Interstate 15 and Pomerado Road, was completed in September. The $9 million facility was funded through a $5.9 million grant from NSF, as well as state, university and private contributions.

José Restrepo, a structural engineering professor (left), and Bob Englekirk, chairman of the board of directors for Camp Elliott. Onlookers stand at the edge of the shake table, which has a 70-foot-tall wind turbine mounted on it. The table is capable of shaking up to 6 feet per second allowing researchers to reproduce realistic simulations of earthquakes. José Restrepo guides a tour underneath the shake table.

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