Caltrans Engineers Massive Bridge Retrofitting Project : Safety: In O.C., two out of 48 structures have already been strengthened following deadly failures in ’88 temblor.

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.

In Orange County, bridges already have been fixed at the interchanges of the San Diego and San Gabriel River freeways and 7th Street (California 22) in Seal Beach. The latter is less than three miles from the the Newport-Inglewood Fault, considered more dangerous to urban areas than even the famous San Andreas Fault.

There are 46 more structures at eight locations remaining to be fixed in Orange County, at a total cost of about $21 million, according to Caltrans. Within a month or two, work will begin on the interchange of the San Diego and Costa Mesa freeways.

Many more structures are not being retrofitted because they will be replaced as part of upcoming freeway-improvement projects, such as the massive Santa Ana Freeway widening effort. The westbound and eastbound Riverside Freeway bridges over the Santa Ana River in Anaheim are being rebuilt now, for example, as part of a car-pool lane project.

“If something has a higher risk, we’re going to pay a lot more attention to it,” said Brett Bennett, a senior Caltrans bridge engineer in Orange County.

From the new structural safety research, engineers have 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.

“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.

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.

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 strengthen. 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.

“There, of course, is no absolute,” he said, tempering his optimism a minute later. “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.

“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.

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. 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.

The old engineering designs on each bridge were re-examined and each construction detail was studied for potential weaknesses.

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.

Seismic Retrofitting

Work has begun on reinforcement of more than 45 structures on seven Orange County freeways so they can better withstand an earthquake. The work will include outfitting the structures with steel jackets or metal rods.

COMPLETED 1. Transition from the northbound San Diego (405) Freeway to 7th Street in Long Beach 2. Transition from the southbound San Gabriel River (605) Freeway to the southbound San Diego (405) Freeway

UNDERWAY 3. Bridge on the Riverside (91) Freeway spanning the Santa Ana River

NEXT 4. Transition bridge from southbound Costa Mesa (55) Freeway to southbound San Diego (405) Freeway

Source: Caltrans; Researched by CAROLINE LEMKE / Los Angeles Times