THE BAY AREA QUAKE : What Next? : PONDERING THE LESSONS, HEALING THE SCARS : Road Engineers Have Few Answers : Transportation: Experts were shocked by the extent of damage to the Nimitz Freeway and Bay Bridge. And they disagree over what must be done to prevent it next time.

It wasn’t supposed to happen this way.

When a major earthquake strikes in California, state officials expect to see plenty of damage. Broken water mains flooding streets. Cracked gas lines setting off fires. Older brick buildings crumbling to the ground.

But freeways and bridges are supposed to stand up under the shaking, with only some buckling and cracking of the concrete.

No one among the state’s top road and bridge engineers thought that a major freeway would simply collapse.

Four years ago, a top Caltrans engineer told a press briefing in Los Angeles that, thanks to improvements made since the 1971 Sylmar earthquake, the state’s highways were now essentially earthquake-proof.

“We feel all the bridges and freeways will go through an event (an earthquake) without collapsing,” Ray J. Zelinski, design engineer for the California Department of Transportation, said at the time.

Even the big one--the catastrophic quake predicted for Southern California--would not destroy an elevated roadway, he said.

Tuesday’s 6.9 quake not only shattered lives and structures in the Bay Area, it also shattered the confidence of the state’s road and bridge builders.

Engineers, though generally an unemotional lot, admitted that they were shocked by what happened Tuesday. Already, there is a demand to know what went wrong and who is to blame. But they also admit that, so far, they can’t supply the answers.

“I’m surprised and very disappointed,” Zelinski said of Tuesday’s disastrous collapse of a portion of Interstate 880, the Nimitz Freeway. “We didn’t think a total collapse was a real possibility.”

From San Diego to Eureka, millions of California motorists drive each day on freeway overpasses held up by concrete-and-steel columns built before 1971. Now, Caltrans engineers say they may face the dauntingly expensive task of reinforcing or even replacing the columns to prevent what happened on the Nimitz.

The collapse of one portion of the San Francisco-Oakland Bay Bridge, though sure to be a haunting scene from Tuesday’s quake, may not forebode a statewide problem. Described as a vintage 1930s-era rigid steel structure, the Bay Bridge is “unique,” said Caltrans spokesman Jim Drago. “There is nothing else like it.”

More recent spans, including the Vincent Thomas Bridge in San Pedro and the San Diego-Coronado Bay Bridge in San Diego, were built to allow some swaying in a quake. Nevertheless, after engineers determine what caused the collapse on the Bay Bridge, they will be fanning out around the state inspecting the thousands of old bridges to see if renovations are required, Drago said.

The freeway overpass problem is more pressing. While the collapse of the Nimitz ended any disagreements over whether the older freeway overpasses pose a danger during a major quake, engineers still disagree over what needs to be done.

Zelinski of Caltrans is among those who believe that the support columns need to be strengthened. The steel rods holding up the columns need to be wrapped in steel bands so that the rods do not buckle and “explode out” during a heavy shake. The state has just undertaken a $64-million, four-year program to add such reinforcements to freeway supports.

But others say the columns need to be made more flexible. Samuel Aroni, a professor at the UCLA Graduate School of Architecture, said the heavy, super-strong but rigid reinforced concrete structures built in the 1960s were not elastic enough. Unable to bend to absorb the tremendous forces generated by an earthquake, they fractured and collapsed.

Still, others are not sure what the proper remedy is.

“Frankly, we don’t have the knowledge to fix them today,” Caltrans chief engineer William E. Schaefer said. Thousands of overpasses, such as those on the Santa Monica Freeway, are supported by rigid, pre-1971 columns, and the Nimitz disaster showed that they are vulnerable to collapse during a powerful temblor.

The answer, said Schaefer, is to do more research, and that alone represents a major change in attitude for Caltrans.

“We felt pretty comfortable” before Tuesday’s quake, Schaefer conceded, because of the recently completed $58-million retrofitting program begun after the Sylmar quake.

After the magnitude-6.4 temblor in the north San Fernando Valley, engineers discovered that the roadways bounced on their support columns, leading to their collapse. To remedy that problem, Caltrans paid to have new steel ties added to hold the road girders onto their support columns.

Tuesday’s quake exposed an entirely different problem. The columns on the two-tiered Nimitz freeway simply buckled and broke.

The Nimitz was unusual in one important sense. The state has relatively few double-decker freeways and none in the Los Angeles area--although plans are under way to double-deck portions of the Harbor Freeway using different, newer techniques than were used on the Nimitz.

But the state has hundreds, if not thousands, of freeway spans held up by rigid reinforced concrete columns similar to those that broke on the Nimitz on Tuesday. These were thought to be strong enough to withstand a major earthquake. That thinking was wrong, at least in the case of the Nimitz.

“We expected damage but not total collapse,” Schaefer said in an interview from Sacramento.

Critics say, however, that if state engineers did not know about the problems posed by the rigid construction techniques used in the 1960s, they should have been warned by the near-collapse of a portion of the 605 Freeway-Interstate 5 interchange during the Whittier quake in October, 1987.

“Any structural engineer could see these (multi-column) structures are vulnerable,” said Aroni of UCLA, an earthquake expert.

“Reinforced concrete buildings of the 1960s were not designed with the understanding of today,” he said. “I am very surprised that (Caltrans) did not realize they are dangerous,” he said. Aroni said it is neither cheap nor easy to upgrade so that the structure can bend and deform elastically and snap back.

“It’s like a paper clip--you can deform it up to a point and then release it and it snaps back to its original shape, but if you bend too much, it will just stay bent and won’t go back to its original shape,” Aroni said.

Some of the reinforced concrete structures built in the 1960s are more brittle and not capable of bending without breaking, as the newer structures have been designed to do, he said. Steel and concrete must be put together so they have the ability to stretch and yield to the gigantic forces of an earthquake without breaking.

State engineers realized that the support columns on older freeways could pose a danger during a powerful quake. They planned a renovation program that focused on those freeways supported by single columns. Freeway overpasses with column supports on both sides were seen as secure--until Tuesday. The Nimitz was a multi-column overpass.

Caltrans engineers stress that it will be some time before they entirely understand what caused the Nimitz disaster.

“We don’t know why it collapsed. We have to find out,” Schaefer said. The Sylmar quake proved to be an important learning experience for engineers, and the officials said they expect the same for the Bay Area quake.

“This quake will teach us what we need to do now,” Schaefer said.