Caltrans to Try Splints on Nimitz : Seismic: If technique works in test on freeway section that withstood quake, they will be installed on similar Bay Area highways.

Caltrans engineers are closing in on a way to strengthen several elevated San Francisco highways similar in design to the portion of the Nimitz Freeway that collapsed in the Bay Area earthquake.

The relatively simple solution would probably have prevented the collapse of the Nimitz Freeway’s Cypress Viaduct, which killed 42 people in the 7.1-magnitude quake on Oct. 17, James Roberts, chief of structures for the California Department of Transportation, said Thursday at a meeting of Gov. George Deukmejian’s commission investigating the failure of the Nimitz.

The technique is similar to the way a homeowner might “sister” a wobbly fence post by tying it to additional support. But in this case, the weak posts are huge concrete columns and the sisters are 10-inch-wide steel beams.

The steel splints are intended to reinforce the joints connecting the upper and lower columns on the double-deck freeways. There is near consensus among engineering experts that the failure of these joints led to the collapse of the Cypress Viaduct.

This week, engineers from Caltrans and half a dozen private consulting firms are attaching the beams to the columns on a portion of the Cypress structure that withstood the quake. Soon, they will use a two-story hydraulic jack to exert 1,300 tons of pressure on the structure, and the engineers will watch to see how the newly buttressed column reacts.

If it works, and Roberts predicts that it will, the department will immediately begin drawing up plans to use the technique on the columns of three San Francisco freeways that were damaged in the quake and remain closed.

The Embarcadero Freeway, the southern freeway portion of Interstate 280 and a leg of the central viaduct on U.S. 101 all could be open by spring, he said. More work might be done later on the structures after the research is complete.

“What this is going to do is guarantee there is no failure,” Roberts said in an interview. “We may get a little cracking, but no failure.”

The quick fix is part of a crash research and development program begun after the quake. Roberts said engineers are working 16-hour days at the site of the collapse, and about 50 of them meet weekly to discuss their progress.

The research project will cost at least $2.5 million, Roberts said, far more than Caltrans has spent on seismic research in the last 10 years.

“It takes an event to bust things loose,” he said.

Caltrans engineers have said that in the past they received all the money they requested for their seismic safety program, even though they knew it was moving slowly. But if the current financial commitment had been made a few years ago, it is likely that this solution or something similar would have been developed in time to save the Nimitz, Roberts said.

“Everything could have been done if you had the money to do it,” Roberts said.

In other developments at Thursday’s commission hearing:

- Vitelmo Bertero, director of the Earthquake Engineering Research Center at UC Berkeley, said he has discovered what he believes to be the weakest link in the Nimitz structure. Bertero said he found two bents--or sets of columns and cross-beams--where horizontal steel bars that were supposed to extend from the road deck into the columns did not do so.

Roberts of Caltrans confirmed that the plans were not followed in the construction of those columns. But Bertero said the columns might have broken even if the proper amount of horizontal steel had been present.

- An Alameda County engineer who was a passenger in a car driving on the structure during the earthquake said the Nimitz seemed to collapse progressively from north to south.

Richard Hendricks, chief of structural design for the county, said he and two other engineers were just coming off the Bay Bridge and onto the Nimitz when they felt the quake. They sped up and managed to drive all the way across the vibrating structure before it collapsed behind them.

“Our main objective was to get off of the Cypress structures as fast as we could,” Hendricks said. “I don’t particularly like high places when they are shaking.”

- Caltrans released an updated schedule of its earthquake strengthening program, including plans to complete the retrofitting of all single-column bridges by the end of 1991. But Roberts conceded that there is little chance that the department can strengthen multiple-column structures by that deadline, which was set by the Legislature.