A badly damaged carpool bridge that links the San Diego and Costa Mesa freeways will be repaired for $3 million to $5 million and opened to motorists by the end of the year, Orange County transportation officials announced Monday.
Plans to fix the flyover, originally built for $12 million, call for adding steel reinforcement and layers of high-strength concrete inside the structure to restore the structural integrity of the span and ensure it can handle heavy traffic loads for at least 75 years. Engineers initially had feared that much of the half-mile connector would have to be ripped out and rebuilt at a cost of more than $8 million.
"We want to ensure that the bridge is safe," said Arthur Leahy, chief executive of the Orange County Transportation Authority. "This is a prudent direction to go."
The 60-foot-tall connector 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. Completion of the entire project, which involves Caltrans, OCTA and private contractors, is expected by the end of the year.
Initially, the two-lane carpool bridge linking the northbound 405 to the northbound 55 and the southbound 55 to the southbound 405 was scheduled to open in April. If repairs go smoothly, the bridge will open at the same time as the rest of the project.
"We are relieved the bridge can be repaired and we can meet our time frame of finishing the interchange project by the end of the year, " said Tim Keenan, a Cypress City Council member who chairs the 13-member OCTA board of directors.
Construction was halted on the connector in late August after work crews found that concrete had cracked and spalled along interior girders that support two of the road's three sections. Spalling is a condition in which concrete falls off in layers or patches.
Engineers suspect that a variety of factors might have caused the damage, including irregularly spaced steel reinforcing bars, thin concrete and too much tension on supporting cables through the middle of the span's concrete girders. Caltrans' design criteria also are at issue.
Hearings to resolve construction disputes will be conducted to determine what caused the damage and who is responsible for paying the repair bill.
For the last three months, teams of engineers and consultants have been working with the designer, CH2M Hill, an international engineering firm, and the builder, C.C. Myers Inc. of Rancho Cordova, to assess damage and propose a repair plan.
Their recommendations were presented Monday during the regular meeting of OCTA's board of directors. The authority is paying for the improvements to the interchange.
Caltrans, a prominent bridge expert and H. Tony Rahimian, CH2M Hill's senior vice president, told board members the bridge can be fixed by removing loose concrete, installing steel reinforcements and applying a 4-inch covering of high-grade concrete over damaged areas.
Reinforcements would include rebar and giant U-shaped bolts to secure bundles of supporting cables. The cables, when pulled tight by hydraulic machinery, keep bridges and elevated roads from sagging.
Engineers said three similarly damaged bridges in California and bridges in Europe have been fixed using the techniques proposed for the O.C. connector.
"This is a solid and proven method," said Freider Seible, a highly regarded bridge expert and dean of UC San Diego's engineering department who was hired by OCTA to assess the bridge and recommend repairs. "Some bridges in Europe were repaired 30 to 40 years ago. There has been no problem with their capacity or serviceability."
In the latest damage assessment, Rahimian said spalling was present in 14 areas of the bridge or along 203 feet of the structure. Cracking was found along 2,887 feet of the span. The length of all girders in the two damaged sections is 7,218 feet.
The flaws, Rahimian said, have reduced slightly the span's ability to carry heavy traffic over its estimated life -- a problem that will be remedied by the proposed repairs. He added that there is no need to tear out the damaged sections as originally thought because the strengthening work needed "can be integrated into the existing structure."