Interstate 80 - Yerba Buena Island Ramps
Owner: San Francisco County Transportation Authority
Lead Design Firm: AECOM
General Contractor: Golden State Bridge Inc.
Structural Engineer: Moffatt & Nichol
Construction Management: WSP
The $58.4-million project to build ramps for Interstate 80 and Yerba Buena Island was a crucial step in the redevelopment of San Francisco’s Treasure Island.
The new westbound ramps provide a longer and safer connection to the San Francisco-Oakland Bay Bridge. The project included five new bridge structures, and the team also moved a historic officers’ quarters to a new site on the island. The only access to the island’s U.S. Coast Guard base was through the site, so the team built temporary roads and added shoring.
Many of the project’s concrete columns are well over 100 ft tall and needed to resist a wind load that increased with height. This is often achieved with an external guying system, with tensioned cables used to add stability. Since space is limited on the island due to adjacent Caltrans work, the USCG base, historical buildings, roadways and the bay, the team used an internal guying system to support column rebar cages against wind loading. The contractor designed a 2-ft-dia rigid steel pipe pile to be cast in the bridge foundation footing. This pipe pile was then grouted and could support several struts to provide stability inside the rebar cage. The project’s most complex parts were the bridge superstructures. Almost every superstructure dimension varied throughout a given frame: bridge width, skew, number of cells, structure depth and girder thickness all constantly changed. The team performed and checked layout so that carpenters could build the forms for pouring concrete to line and grade.