Innovative Design for the SFOBB I-80 WB Ramps at Yerba Buena Island

Abstract

San Francisco County Transportation Authority (SFCTA) selected AECOM and Moffatt & Nichol for the design of the new westbound entrance and exit ramps providing access between the new east-span of San Francisco-Oakland Bay Bridge (SFOBB) and Yerba Buena Island (YBI). The purpose of the project is to improve mobility, safety, and access by replacing two westbound existing ramps on I-80 constructed in the 1930s. The new ramps will be a significant improvement geometrically and operationally over the current ramps. They include bridge structures that complement the SFOBB architecture. The project was cleared under an EIR/EIS prepared by AECOM. The construction contract of the project has been awarded in late 2013, and construction completion is targeted for late 2016. The YBI WB on and off ramps consist of five structures: YBI WB Tie-In Viaduct (Widen) - a five-span cast-in-place prestressed concrete box girder supported on large-diameter CIDH foundation; YBI Transition Viaduct (On-Ramp Widen) - a two-span cast-in-place reinforced concrete box girder with a variable depth supported on driven pile foundations; YBI WB On-Ramp Structure - a two-frame, five-span concrete structure supported on driven pile foundation; YBI WB Off-Ramp Structure - a two-frame, six-span concrete structure; and YBI WB Transition Viaduct (Off-Ramp Widen) - a cast-in-place concrete deck with a single structure steel box girder. The WB Ramp Structures were designed to resist two-level earthquake, including a Functional Evaluation Earthquake (FEE) with a return period of about 92 years and a Safety Evaluation Earthquake (SEE) with a return period of about 1500 years. The terrain at the bridge site is highly variable with ground surface elevations varying from about +10 m to about +50 m.