Putting Bridges on Firmer Foundations : Safety: Collapsing structures killed 42 people during the Loma Prieta quake, galvanizing a seismic retrofitting effort. The massive project, although unfinished, has made major improvements.

Out of the darkest moment in its history, the California Department of Transportation has fashioned what it hopes will be recognized as the world’s most extensive and technologically advanced earthquake retrofitting program for highway bridges and overpasses.

In the four years since the Loma Prieta earthquake shook apart two major bridges, sending 42 people to their deaths, Caltrans has embarked on a retrofitting program of unprecedented scale, conducting new research and spending millions of dollars to strengthen bridges.

From the research, it has produced new techniques for toughening structures, determined ways to predict how earthquake forces will affect individual bridges and developed methods for testing the ability of retrofitted bridges to withstand the rocking and shaking from temblors.

Caltrans has used a variety of new methods to increase bridge resistance to earthquake forces, including fitting columns with steel jackets, enlarging footings and attaching concrete supports along the edges of long bridge decks.

“In terms of seismic retrofit there’s no question that California is the leader worldwide,” said Frieder Seible, professor of structural engineering at UC San Diego, which has done much of the research for the state.

Indeed, no other country has strengthened as many bridges as California, and the program is unfinished.

So far, $393 million has been spent on retrofitting that is either completed or well under way on 604 elevated structures on the state’s most heavily traveled freeways. Retrofitting strategies for another 412 structures are being devised, and 340 bridges are being analyzed to determine if they need strengthening. The final bill for the program, which is scheduled to be finished by the dawn of the new century, is expected to reach $1.5 billion.

Although the Loma Prieta quake struck the San Francisco Bay Area, retrofitting work is further along in the Los Angeles Basin, where seismologists believe the next large quake is most likely to occur. The retrofitting of all major highway interchanges in Los Angeles considered vulnerable to earthquake damage is either under way or completed.

The first contracts for the last big project, a five-mile elevated segment of the Santa Monica Freeway, stretching from the Harbor Freeway to the Los Angeles River, were awarded in late summer.

In the San Francisco Bay Area, most major interchanges and the massive double-deck freeways similar to the one that collapsed in Loma Prieta have also been strengthened, but the biggest projects and the most difficult and expensive retrofitting jobs lie ahead.

Saved for the latter years of the program have been the state’s toll bridges, including the San Francisco-Oakland Bay Bridge, the most complex elevated structure in California and one that will cost about $200 million to retrofit. The bridge sustained some damage during the Loma Prieta quake.

Jim Roberts, the Caltrans director who has headed the retrofitting effort, believes that research has advanced so far since Loma Prieta that when all the strengthening is completed, Californians will be able to travel their highways with “peace of mind.”

“I think you can drive any place on any highway in the state and you may have rock and roll once in a while but, in my opinion, you’re not going to have a bridge tragedy,” he said in an interview.

A few minutes later, he tempered his optimism slightly. “There, of course, is no absolute,” he says. “But I think we can honestly say, as well as anybody in the world, that we can prevent collapse, that we can prevent major damage.”

That, Roberts says, is the “silver lining” in the Loma Prieta tragedy--the fact that the deaths of 42 people spawned a program that could save thousands of lives.

Indeed, no other natural disaster has had a greater impact on Caltrans than Loma Prieta, which literally shook the very foundations of the agency’s road-building program. Until Loma Prieta hit on Oct. 17, 1989, only two people had died on California highways as a result of earthquakes. Seismic retrofitting was treated as a poor stepsister, underfunded and low in priority compared to other Caltrans programs.

After Loma Prieta, the vulnerability of California’s bridges was spotlighted around the world. Earthquake safety became a prime goal for Caltrans and the state’s political leaders. Then-Gov. George Deukmejian appointed a board of inquiry to examine the damage from the quake and make recommendations for changes in the retrofit program.

The Legislature ordered Caltrans to make seismic safety a top priority and set deadlines on bridge retrofitting.

“In the past, the attitude may have been that seismic retrofit was a necessary evil. The attitude after Loma Prieta was: ‘Let’s do everything we can do to make sure that we never have that kind of disaster again,’ ” said Assembly Transportation Committee Chairman Richard Katz (D-Sylmar). “In the engineering community there became almost a missionary zeal about this earthquake work.”

With the collapse of a nearly two-mile stretch of the double-deck Nimitz Freeway in Oakland and a 50-foot section of the Bay bridge’s upper deck, Loma Prieta not only exposed structural design problems on the bridges but, even more important, flaws in the department’s entire approach to retrofitting.

Calling Loma Prieta “a clear and powerful warning,” Deukmejian’s panel said Caltrans’ retrofitting program had been driven purely by experience. If an earthquake revealed a weakness in bridge design, Caltrans would move to correct it. Loma Prieta showed, the panel said, that those weaknesses had to be uncovered before a quake struck.

“Before Loma Prieta they (Caltrans) would wait to get a kick before they moved. Now that attitude’s out. That’s gone,” said George Housner, engineering professor emeritus at Caltech who headed Deukmejian’s inquiry.

As a result, the department decided to examine 7,000 of the state’s 13,000 bridges, culled those that would need retrofitting and set priorities for which would be done first. Initial retrofitting estimates soared from $300 million to $1.5 billion.

A bridge’s position on the priority list was determined by its proximity to an active fault and the kind of soils that anchored it. Structures nearest faults and on soft soils, like those that anchored the Nimitz, were scheduled for immediate overhaul.

The number of people who could be killed or hurt in a bridge collapse was also calculated, and structures carrying heavy traffic were put high on the list.

Likewise, if their collapse could affect another artery--a road or railroad underneath, for example--or if their closure could cut off access to a hospital or other critical facility, they were given top priority. Consequently, interchanges such the Interstate 10 connection with I-405 and the I-405 connection with the I-605 were among the first projects completed.

The old engineering designs on each bridge were re-examined and each construction detail was studied for potential weaknesses. Single-column bridges, proven vulnerable in previous earthquakes, and those with hinges similar to the ones on the Nimitz rose to the top of the list.

The year a bridge was designed became important. Those built after the 1971 San Fernando Valley quake, which prompted radical changes in the way Caltrans designed bridges, were found to be strong and tough. The same was true of structures built in the 1940s--before the age of computers, when cautious engineers over-designed bridges to compensate for their inability to precisely calculate loads and stresses.

The years to worry about, Caltrans officials concluded, were the 1950s and 1960s, when much of the state’s freeway system was built.

Simultaneously, the research arm of the program was developing ways to simulate the effect of earthquake forces on individual bridges by building large scale models at a UC San Diego laboratory.

“We can determine how far we can push a structure until it collapses and then we can determine how much the earthquake is going to try to push it. We compare the two numbers and we’ve got some idea how resistant it is to earthquake,” Roberts said.

Using that knowledge, Roberts said, Caltrans is customizing its retrofit designs to each bridge.

For the interchange connecting the Ventura and Glendale freeways in Glendale, Caltrans determined that the nearest fault, known as the Malibu-Santa Monica-Raymond Fault, could produce a maximum earthquake of magnitude 7.5.

A quake of that magnitude, they predicted, would produce shaking for 24 to 35 seconds, putting severe stress on columns and expansion joints. The retrofit strategy called for installing steel shells around the columns, strengthening the footings and upgrading the hinges that connect columns to the bridge decks.

As the retrofit program nears the midway point, Roberts and other engineers say they no longer worry whether the job can get done, but whether the money will be there to pay for it.

Ian Buckle, an engineer who is deputy director of the National Center for Earthquake Engineering Research in Buffalo, N.Y., said money for research and retrofitting traditionally dries up as memories of the last big quake begin to fade.

“In this day and age, given the state’s economic situation, seeing this amount of money spent for both research and strengthening the bridges is a surprise,” he said. “For it to be sustained for four years is remarkable.”

Seismic Strengthening

Seismic retrofitting of major freeway interchanges in the Los Angeles area that are considered vulnerable to earthquake damage is either under way or has been completed. Work done on about 100 bridges has cost $33 million; construction is being done on another 40 bridges at a cost of $19.9 million.

The bridges targeted for retrofitting were built mainly during the height of freeway construction, during the 1950s and 1960s. Those constructed after the 1971 Sylmar earthquake and those built in the 1940s were judged not to need retrofitting.

Completed retrofitting Highway 90 and I-405 (San Diego Freeway) Highway 134 and I-5 (Golden State Freeway) Highway 134 and Highway 2 I-5 and I-110 (Harbor Freeway) I-405 and I-10 (Santa Monica Freeway) Highway 57 and Highway 60 I-405 and I-110 (Harbor Freeway) *

Undergoing Retrofitting I-10 and I-110 I-5 and Highway 118 Highway 60 and I-605 (San Gabriel Freeway) I-710 (Long Beach Freeway) and Highway 60 I-10 (Santa Monica viaduct from West Los Angeles)