In order to complete the new east span of the San Francisco-Oakland Bay Bridge it was necessary to relocate bridge traffic onto a temporary by-pass. This will allow the existing steel truss viaduct between the Yerba Buena island tunnel and the existing cantilever truss span to be demolished to make room for construction of the new Yerba Buena island viaduct that will connect the tunnel to the main self anchored suspension span of the new Bay Bridge. Main components of the by-pass were the West and East Tie-ins. These structures, which were completed in 2007 and 2009, respectively, were built to the side of the existing viaduct and moved into place over a long weekend in which the bridge was closed to traffic.

The West Tie-in was a concrete structure that was skidded into place using 2500 kip jack shoes designed to skid. Mr. Valentine designed the supports for these jack shoes.

The East Tie-in was a 288 ft long double-deck steel truss that was approximately 70 ft. wide and designed to carry 10 lanes of traffic. It was constructed approximately 150 feet above ground on specially designed steel skid bents and skid beams. At the appropriate time the existing truss span was also supported on the skid beams and cut free from its bearings. It was then skidded to the north on the same type of jack shoes used on the West Tie-in. This required retrofitting of the existing viaduct to stabilize it against earthquake motions once the existing truss span was removed. The existing truss also had to be retrofitted to resist the redistributed loads generated by lifting the truss at internal panel points and to accommodate the resulting truss displacements.

When the existing truss was moved out of the way, the new truss was skidded into place and set on its new bearings. New expansion joints and barrier rails were placed and traffic routed onto the new by-pass structure.

Mr. Redfield and Mr. Nutt were involved in this project from its conception. Mr. Redfield designed the expansion joint and barrier rail system and much of the retrofitting of the existing viaduct. He also advised the project on all of its aspects and organized and helped produce the construction drawings for this project. Mr. Nutt helped develop design criteria for the project; designed the skid bents and their foundations, the skid beams, the permanent bent at the west end of the new truss span, bearing restraints, and retrofitting of the existing truss span. He also reviewed the span movement contractor’s procedures and support mechanism design. The project was completed only one hour beyond schedule despite discovery of an unrelated cracked eye-bar in another portion of the bridge.