Bridge Quake-Proofing Passes a Key Test : Retrofitting: Technology shows way to repair structures damaged in 1989 temblor.
A technology designed to allow California’s bridges to withstand a jolt from a major earthquake has been successfully tested at UC San Diego--paving the way for the reopening of two viaducts closed after the 1989 Loma Prieta quake, researchers said Tuesday.
With the new technology, engineers believe retrofitted bridges will be flexible enough to bend with a major earthquake and sturdy enough to withstand extreme force--a design the state Department of Transportation hopes to use to avoid a disaster such as the collapse of a mile-long stretch of the Cypress viaduct section of the Nimitz Freeway in Oakland that killed 42 during the quake.
“UCSD has produced a proven, safe and cost effective design,” said Jim Roberts, chief of Caltrans’ division of structures. “The retrofit techniques we are developing in California will be the model for the rest of the world.”
The concept behind the design and the technology, touted as revolutionary, could be used to retrofit more than 1,000 bridges in the state, Caltrans spokesman Jim Drago said from Sacramento.
Caltrans had been awaiting UCSD’s final test results--including subjecting a bridge model to a simulated earthquake--before using the design on the state’s older double-deck bridges, including the damaged U.S. 101 and the Interstate 280 viaducts in San Francisco, which have been closed since the 1989 temblor.
The “edge beam” design passed recent tests with flying colors--clearing the way for construction to begin on the U.S. 101 viaduct, for an estimated $60 million, and the Interstate 280 viaduct, for an estimated $90 million, Drago said.
The new technology features a beam supported by circular columns running along the outside of the bridge.
For the test, researchers used 13 computer-controlled hydraulic jacks to generate a force greater than a magnitude 8.0 earthquake on the San Andreas Fault, which is considered the maximum possible for a future earthquake in San Francisco, said Frieder Seible, professor of structural engineering at UCSD and co-investigator of the project. Each computer is capable of triggering 260,000 pounds of force.
The testing included a two-week around-the-clock earthquake simulation of a retrofitted, half-scale bridge model, which was 50 feet long with columns 10 feet and 6 feet high. The bridge model was outfitted with 350 instruments to monitor stress, displacement, rotation and tilt during the simulated earthquake.
While it will take about two years to analyze the data fully, Seible said he expects to send a preliminary report to Caltrans officials within the next few days.
Based on the test results, Caltrans will award a contract and begin work on the U.S. 101 viaduct, which is expected to be completed by mid-1992, and the Interstate 280 viaduct, which should be finished by late 1992, Drago said.