Three Possible Causes of Ramp Flaws Investigated

Engineers are investigating whether thin concrete, irregularly spaced steel bars and over-tightened reinforcing cables caused extensive damage to a new $12-million carpool bridge connecting the San Diego and Costa Mesa freeways, newly obtained Caltrans records show.

According to the documents obtained by The Times under the California Public Records Act, some engineers studying the flawed span suspect that builders put too much tension on supporting cables, causing concrete girders to crack and spall, a condition in which concrete breaks off in layers.

The damage has been found in two of three sections of the half-mile-long span, delaying the April 2003 opening perhaps eight to 10 months.

To keep such large bridges and elevated roads from sagging, long steel tendons are installed inside them. These cables, which run through metal pipes in concrete girders, are pulled tight by hydraulic jacks to tension levels set by designers.

Even if the proper amount of tension was used on the cables, the Caltrans records suggest, the damage might have occurred anyway because of thin concrete and uneven spacing of steel reinforcement bars. In some of the damaged spots, the amount of concrete that covered the rebar was found to be only two-thirds of what the design required.

“It appears that there are locations where the concrete cover of the [rebar] is less than planned,” a Caltrans engineer wrote in an Oct. 28 report. As built, he said, the sections where damage was found might have been “inadequate to resist” the proper amount of tension, let alone any excessive force.

Based on field data, the engineer wrote that the tension applied to cables in the two girders appears to exceed the maximum force needed.

The Caltrans reports, fact sheets and technical analysis provide a glimpse into the effort to assess the damage, pinpoint the cause and repair the 60-foot-high ramp. At stake, too, is determining who is at fault and who will pay for repairs that could cost more than $8 million if -- in a worst-case scenario -- sections of the elevated roadway must be torn down and rebuilt.

The towering span is part of a $125-million effort to improve the junction of the San Diego and Costa Mesa freeways, one of the nation’s 10 busiest interchanges. Though Caltrans oversees the project, it was designed by CH2M Hill, built by C.C. Myers Inc. and paid for by the Orange County Transportation Authority. About 20% of state highway projects are contracted to private firms.

Jon Rohrer, an area construction manager for Caltrans whose duties include working on bridges, said the thin concrete, the spacing of rebar and the possibility that too much force was applied to the bridge’s cables are all being investigated as possible causes of the structural failures.

“We have not ruled out anything yet,” Rohrer said.

Work was stopped Aug. 20, when construction crews found that concrete had cracked and fallen off girders that support two of the road’s three sections. The girders are contained in large bays that run the length of the curving bridge.

For the last two months, teams of engineers and consultants have been assessing the damage and developing a repair plan. No conclusions have been reached yet.

“This is very complicated; a lot of issues are in play,” said Rick Grebner, an OCTA project manager. “It’s too early to definitively say what caused this. Our focus has been on fixing the road and getting it into service.”

Caltrans contends that the designer and the builder are responsible for the damage and must make repairs. The transportation department has given both firms until the end of the month to find a solution.

The builder and design firm have agreed to do the repair work but under protest. Both have given notice that they intend to file claims against Caltrans. At issue is whether the agency’s design guidelines for the bridge were adequate.

Representatives for C.C. Myers of Rancho Cordova declined to comment and referred all inquiries to Caltrans.

Tom Peters, a spokesman for CH2M Hill, defended the international engineering firm’s track record, saying it has planned many successful bridge projects in California. “We designed the bridge to every professional standard,” Peters said. “We are still exploring all the options for repair. I’m confident we are making good progress. Something should be forthcoming in the next few weeks.”

If two of the three spans must be rebuilt, C.C. Myers has estimated, it would cost $8.3 million and take about 10 months.

Caltrans records show, however, that other options are under discussion. They include replacing the damaged girders.