Kobe Quake Offers State Few Lessons on Bridges : Safety: Caltrans engineer tells seismic conference that spans in California are stronger than those in Japan. But he warns that structures in Midwest, East are vulnerable.

The damage sustained in this year’s Kobe earthquake demonstrated that California bridges are superior to those in Japan and that there are few lessons to be learned from Kobe in bridge retrofits, a senior Caltrans engineer said Monday.

Mark Yashinsky of the California Department of Transportation’s Office of Earthquake Engineering, speaking to a U.S.- and state-sponsored National Seismic Conference on bridge and highway retrofitting, said, “No changes are currently anticipated in Caltrans’ design procedures as a direct result” of Kobe.

The Japanese “saw many non-ductile [rigid] bridges collapse, and many new bridges that were designed for too small a load had serious damage,” Yashinsky told 400 engineers and other attendees from the United States and several other countries.

He said Japanese experts who came to Los Angeles to observe damage from the 1994 Northridge earthquake had concluded that strong ground acceleration readings recorded during that quake were incorrect. “If they had believed in these accelerograms, they would have realized” that the safety margins used for designing Japanese bridges were “far too small,” he said.

In his unusually blunt assessment, Yashinsky warned, however, that the eastern and central United States could learn from what happened at Kobe, because the steel girder superstructures damaged there were similar to many bridges in the East and Midwest “and because the size of the earthquake was much larger than was anticipated, a situation that could occur” back East.

The difference in California is that Caltrans has anticipated much larger earthquakes and that the latest developments with retrofitting, giving bridges the ability to bend without breaking, will provide more protection here than existed in Kobe, he said.

However, one area in which the Japanese are ahead, he said, is in modifying soft soils subject to liquefaction before building bridges in them. The Santa Monica Freeway collapse in the Northridge earthquake took place in an area of soft soils.

Yashinsky’s remarks followed assurances from James Roberts, director of engineering services for Caltrans, that California’s retrofit program is “zinging ahead,” particularly in Southern California, and that it is the right thing to do “because on the average you can get a retrofit for 10% of replacement cost.”

No such optimistic national picture came from Anthony R. Kane, executive director of the Federal Highway Administration. He said the nation has 595,000 bridges, that 60% of them were constructed before 1970 “with little or no seismic consideration” and that retrofitting has barely begun in most of the 31 states with earthquake risk.

The nation is spending $6 billion a year to maintain its bridges and it should be spending $9 billion, Kane said. But with Congress in a budget-cutting mood, there is little prospect of that, much less a major retrofit effort, he said.

Complacency, he warned, is a major problem. “The further we get away from a disaster such as Northridge, the less the impetus for high officials to consider it as they wrestle with allocating resources,” Kane said.

On Sunday, before the conference began, about 90 participants toured UC San Diego’s Charles Lee Powell Structural Research Laboratories, where much testing is conducted for Caltrans on the latest bridge retrofit techniques.

Prof. Frieder Seible, who hosted the tour, emphasized Caltrans’ preoccupation with new composite materials used to wrap bridge columns to protect them from collapse.

Seible said that, while more expensive than steel jackets now used to wrap columns, composite jackets will become cheaper to use when they are mass-produced. “They’re not that interesting yet, but they will be,” he said.

Roberts, in his talk Monday, also emphasized the use of seismic base isolation--in which huge shock absorbers reduce shaking of structures--as a retrofit technique. This would be particularly useful, he said, on older bridges that are not so well designed as more recent ones to resist earthquakes.