Seismic Testing of Old Navy Pier Shows What Could Happen During 'Big One'
November 12, 2003
Contact: Christina S. Johnson, csjohnson@ucsd.edu, 858-822-5334
Instruments called accelerometers record the pier's response to an applied force. By placing three of these instruments at right angles to each other, all accelerations in the horizontal and vertical directions are recorded. Photo: UC San Diego, Department of Structural Engineering
If recent seismic tests at the Port of Long Beach are any indication, old working piers in California may be less prone to collapse during moderate earthquakes than previously thought.
This was a conclusion from a series of field experiments led by Scott Ashford of UCSD's Jacobs School of Engineering and funded in part by the National Sea Grant College Program.
In May 2003, Ashford and his team vibrated and shook a 50-year-old former Navy pier to gauge how the massive, 1,500-foot structure would respond to ground shaking - and to validate new seismic design criteria for marine oil terminals in California.
The most dramatic experiments were "lateral load tests" in which a series of hydraulic pistons pushed laterally against one side of the pier. Under extreme loads, sections of the top of the pier were moved about four feet relative to the pier's base about 40 feet beneath the waterline.
The metal pole is an "actuator," a giant hydraulic piston. With great force, it pushes against the pier's side. Photo: UC San Diego, Department of Structural Engineering
The resulting structure looked like some odd rendition of the leaning tower of Pisa with modern touches
of cracked concrete and bent metal reinforcement. Significantly, however, the tilted pier never collapsed.
"We were all surprised by how ductile it was," Ashford said. "More ductile means more earthquake resistant. It just kept on going. We kept pushing it, and it did not fail. We expected the pier to perform poorly."
The San Andreas fault, along with its complex network of sister faults, makes California one of the most seismically active regions in the country. Because of the region's high seismic risk, building codes for homes, hospitals and schools are among the strictest in the nation.
The California State Lands Commission is now implementing new design criteria that will extend this level of protection to marine oil terminals - huge piers where supertankers pipe oil into holding tanks on land.
A 5,000-pound rotating shaker vibrates sections of the pier at different frequencies to identify the structure's natural harmonics. More vigorous shaking simulates ground motions that might be felt during an earthquake. Photo: UC San Diego, Department of Structural Engineering
The goal is to reduce the chances that moderate earthquakes will cause disastrous oil spills. There are about 60 marine oil terminals in ports such as Long Beach, Oakland and Los Angeles that may need retrofitting to meet new standards.
Ashford's experiments were designed to gather information on how to retrofit these piers, with a broader goal being to revitalize the nation's port infrastructure. As he and graduate students continue to analyze data gathered during the tests, what is learned will be shared with port authorities, oil companies and other interested parties in a series of educational workshops to be held at all major ports in the state.
An ultimate goal is to improve computer simulations of how a structure might respond during an earthquake. The data gathered during this project will help in this effort. "These tests will give us some confidence that when we use our computer models, they are predicting what will happen in reality," Ashford said.
A hydraulic piston bolted to two sections of the pier slowly expands, subjecting the pier to lateral loads that might be experienced during an earthquake. Photo: UC San Diego, Department of Structural Engineering
Engineers rarely have opportunities to conduct full-blown, destructive tests on real marine structures. Usually, seismic tests are performed on model structures put on shake tables. The opportunity to "shake" Pier 3 arose because the port planned to demolish it as part of its $500 million upgrade of port infrastructure.
The Long Beach/Los Angeles port complex has become America's gateway to Asia. Together, they handle more containers than any other port complex in the nation. The Port of Long Beach, the Port of Los Angeles, the State Lands Commission and the construction companies Manson Construction-Connolly Pacific JV, Han-Padron Associates, and Penhall Company provided support for Ashford's Sea Grant research.
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