Questions on Reinforcing of Freeways Raised

With sobering force, Monday’s earthquake devastated much of Southern California’s massive roadway system, causing officials to begin reassessing a $1.5-billion reinforcement program designed to prevent the state’s highways from buckling under seismic stress.

The magnitude 6.6 quake caught state highway engineers in the midst of a costly program to reinforce or retrofit key freeway bridges and interchanges that were considered vulnerable to large temblors.

Despite that program, portions of six freeways were closed because of structural damage. The hardest hit were two of the region’s busiest routes: the Santa Monica Freeway near La Cienega Boulevard, where an elevated portion of roadway buckled onto the street below, and the Golden State Freeway, which was closed by the collapse of an Antelope Valley Freeway overpass. The collapses caused sections of all three freeways to be shut down.

Parts of the Santa Monica Freeway are expected to remain out of service for a year to 18 months.

“We had what you would call a catastrophic collapse” of those highways, said Jim Drago of the California Department of Transportation in Sacramento. “This was a surprise. Obviously the structures did not have sufficient strength to ride out the forces they were hit with today.”

Drago noted that most portions of the roadway system that were reinforced came through intact, underscoring the importance of the retrofitting program launched after the 1971 Sylmar quake, which toppled freeway overpasses. But the widespread destruction of freeway bridges and overcrossings Monday was a source of consternation among state leaders who thought that the most vulnerable roadways had already been shored up.

Caltrans Director Jim Van Loben Sels said the segments of the Santa Monica Freeway that collapsed at La Cienega Boulevard and Fairfax Avenue were to have been retrofitted this spring.

“We had our bridges rated by risk and we had completed our high-risk ones, and we were just moving on to medium risk,” he said. “In some sense, our program performed well, but not well enough. We didn’t get them all.”

The failure of vital traffic arteries will spark a renewed effort by Caltrans to evaluate highways that may be in need of reinforcement, using data from Monday’s quake to refine their seismic safety engineering, officials said.

Gov. Pete Wilson, asked whether a special inquiry into the retrofitting effort might be warranted, said: “I don’t think it would be appropriate. I think what we are more interested in doing now is repairing damage, making people safe.

“But if an inquiry is in order . . . let it proceed.”

Sen. Dianne Feinstein (D-Calif.) said she hoped the state would look into the progress of the retrofitting program on the theory that all freeways should be able to withstand a moderate-size quake similar to Monday’s.

A key question facing highway officials was why some of the crippled roadways, such as the Santa Monica and Golden State freeways were considered a relatively low priority, since they failed under far less force than might have been expected if the Big One had struck.

Recalling the collapse of Oakland’s Nimitz Freeway in 1989, Feinstein noted that highway officials are still learning about the inexact science of determining how roadways will respond to shaking and bending in an earthquake.

“We need to really upgrade our state-of-the-art preparedness and construction in earthquake zones, particularly freeway construction,” she said. “That’s where you have the largest loss of life.”

Monday’s quake caused no fatalities on the Santa Monica Freeway, the nation’s busiest. But three different overpasses on the route partially buckled, causing enormous concrete slabs to move and crumble. Observers described its undulations as a horrific pre-dawn spectacle.

“When I came outside, the freeway was dancing up and down,” said Lacy Loeb, who lives a block from the freeway. “The whole structure mushroomed one second and then dropped the next.”

Overpasses at Fairfax Avenue and at Venice and La Cienega boulevards suffered severe damage. At Fairfax, the freeway shifted so that a four-foot wall of concrete rose up in the middle of the traffic lanes. At Venice, the support structures underneath the freeway were crushed by the falling concrete, exposing twisted steel supports.

Caltrans workers at the scene estimated that the overpasses would have to be torn down and rebuilt.

In a 1982 assessment by the state Division of Mines and Geology, the ground near the point of the collapse was identified as being prone to liquefaction--the breakdown of water-saturated soil when subjected to shaking.

But that section of the Santa Monica Freeway was given a lower priority for retrofitting than other projects because the freeway overpasses already had multiple support columns, said Caltech professor Wilfred Iwan, head of the California Seismic Safety Commission.

The damaged stretch of the freeway happened to be one of the next in line for being shored up, according to Jim Roberts, chief of Caltrans’ retrofitting program. The $3.7-million job was to have gone to bid next month, and was scheduled to take about a year, he said.

Steel jackets that would have been installed around the concrete supports most likely would have prevented the collapse, Roberts said. “From the pictures, it looks like the columns just shattered,” he said.

Transportation officials said some ramps adjacent to the collapsed roadway withstood the quake because they already had been retrofitted.

Near Santa Clarita, where the Golden State and Antelope Valley freeways merge in a towering concrete maze, cars were scattered Monday at two places where the road abruptly ended.

One big-rig truck had jackknifed just before a precipice that was formed when the quake split the road in two. The huge highways were scarred with cracks, and chunks of concrete from upper levels of the interchange had collapsed and crashed to the roads below.

That freeway junction was also scheduled for retrofitting, but the work had not yet been done, Caltrans officials said. “We didn’t consider (the overpasses) quite this vulnerable,” Roberts said. “We thought we had time.”

Caltrans officials acknowledged that they erred in a decision not to retrofit bridges along the Simi Valley Freeway (California 118) in the San Fernando Valley. Those bridges also collapsed.

An evaluation of the bridges, constructed five years after the 1971 Sylmar temblor, convinced engineers that they were strong enough to withstand a severe quake, officials said.

Monday’s quake was apparently centered on an unmapped fault in the San Fernando Valley, said Roberts, who said the discovery will add to the work of highway engineers.

“Now we’ll have to re-evaluate a whole lot of bridges close to this new fault,” he said. “That means we have to go back and rescreen several hundred bridges that are within a certain distance of this new fault line.”

In addition to that work, Caltrans engineers will be examining all freeway bridges and overpasses within a 50-mile radius of the quake’s epicenter for any sign of damage, officials said. An investigative team of engineers and seismic experts will conduct a detailed analysis to determine what happened to each of the damaged bridges.

Retrofitting has been the state’s way of bolstering existing freeways--especially those built before the 1971 Sylmar quake--to withstand the sharp movements of California’s fragmented crust.

The program took on increased urgency after the Whittier Narrows quake in October, 1987. That magnitude 5.9 temblor threatened to bring down a major interchange connecting the San Gabriel River Freeway and the Santa Ana Freeway between Santa Fe Springs and Downey.

Subsequently, Caltrans began accelerating its efforts to reinforce freeway bridges, but the task is daunting. There are about 12,000 freeway bridges in the state, and engineers had to evaluate the soundness of those bridges before establishing a priority list.

The 1989 Loma Prieta quake near Santa Cruz gave further impetus to the program because of the 43 lives lost in the collapses of the double-decked Nimitz Freeway in Oakland and a portion of the San Francisco-Oakland Bay Bridge. Since then, two-thirds of the retrofitting work has been done in the Los Angeles Basin. “I always felt that the next one would come in L.A.,” Roberts said.

Before Monday’s quake, most major interchanges in the Los Angeles area had been reinforced or were in the process of being retrofitted, Caltrans officials said. Often, that bolstering involves wrapping the concrete columns that support freeway bridges with steel jackets. Or in some cases, the base of the columns and the edge of longer bridge spans are enlarged to provide additional support.

Roberts cited the critical interchange of the San Diego and Santa Monica freeways as one that may have been spared by retrofitting from serious damage or collapse.

“This earthquake shows that what we’ve been doing works,” he said.

Iwan of Caltech said, “There’s always a question (whether) we could do things faster. Basically, if we had more money we could progress at a lot faster pace, but there are a lot of things that compete for the same dollars. We have social problems and a lot of other problems that society wants taken care of.”

George W. Housner, a worldwide authority on earthquake engineering, said he suspected that every building, road or bridge that failed Monday either was not constructed in accordance with seismic codes or had not been retrofitted after the 1989 Loma Prieta quake.

“My guess is that when all the information comes in, we’ll say, ‘Yes, they should have come down,’ ” said Housner, who chaired a state panel that investigated and made recommendations following the Northern California quake.