Image Courtesy of Caltrans

Steel shims inserted between bearings will dissipate earthquake energy.

The opening date for the San Francisco-Oakland East Bay Bridge has been moved back to the original date of Tuesday, Sept. 3. The bridge opening had been postponed until December to allow time for contractor American Bridge/Fluor Joint Venture to install permanent saddle braces to replace the clamping force lost when corroded steel bolts broke during tensioning in March.

Shortly after announcing the delay in July, the bridge's seismic review panel recommended an interim fix to shim the bearings on the east pier as a way of replacing the seismic performance lost from the shear keys that are located where the bolts failed, says Steve Heminger, chairman of the Toll Bridge Program Oversight Committee. The Federal Highway Administration and independent bridge engineers vetted and approved the proposal.

Benicia Fabrication & Machine, Benicia, Calif., fabricated the Teflon-coated steel shims at a cost of $250,000. Crews will install them around four bearings in the east pier to temporarily prevent the bearings from moving longitudinally and transversely. Tony Anziano, toll-bridge program manager for Caltrans, says the Teflon coating will still allow the bearings to rotate, but the shims also will function as shear keys and provide an increased safety factor in the event of a seismic event until the permanent fix is in place later this year. The cost for the temporary and permanent fixes is expected to be approximately $23 million.