SAN FRANCISCO — Officials are studying a temporary fix for cracked seismic safety bolts on the San Francisco-Oakland Bay Bridge that could allow the new span to open as scheduled on Labor Day, but they said Wednesday a decision had not yet been made on the work.
At this point, members of the Toll Bridge Program Oversight Committee said, the longer-term repairs were still scheduled to be finished by Dec. 10.
Engineers were looking at a “shimming” idea — installing steel plates into the area of the broken bolts to help prevent movement during an earthquake, said Steven Heminger, an oversight committee member.
The temporary fix would be in place while long-term repairs occurred, he said.
The cracked bolts have derailed the opening of the eastern span and led to millions of dollars in cost overruns on the $6.4 billion project.
The existing bridge, built in the 1930s, is not considered earthquake-safe, and years of cost overruns and construction and design delays have plagued the new project that had been scheduled to open on Labor Day with great fanfare.
The current problems started in March, when 32 of the 17-foot-long bolts that secure earthquake shock absorbers to the deck of the bridge were tightened.
Tests found that hydrogen had infected the bolts, which were also made of poor quality steel, making them brittle. When tightened to high tension, the brittleness gave way, causing the cracks.
An investigative report faulted all entities involved in the design and construction of the bolts — the California Department of Transportation, bridge engineers at T.Y. Lin International/Moffatt & Nichol Design; and contractor American Bridge-Fluor Joint Venture.
For example, investigators found that construction crews left the faulty bolts in open ducts for five years, exposing them for long periods to rainwater and marine air.
Investigators also faulted all parties for choosing to subject the bolts to “hot-dip” galvanizing, a corrosion protection process that exposed them to the high heat that can increase brittleness and susceptibility to hydrogen.
Heminger said all parties should help pay for the repairs.
“If there’s shared responsibility, we think there ought to be shared financial responsibility,” Heminger said.
Investigators said a faulty design also complicated repairs. The failed bolts were installed in an area of the bridge beneath a concrete cap that made removal impossible.
The permanent repair is a steel saddle that would replace the clinching function of the failed bolts. It has been estimated to cost about $20 million.
Officials said a review of other bolts throughout the structure have found no further problems, easing concerns that they could also have become brittle from exposure to hydrogen.