Summer 2019

ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.

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Page 13 of 55

The Salesforce Transit Center (STC) i s a re g i o n a l t r a n s i t h u b l o c a t e d in the heart of San Francisco, Calif. T h e m u l t i l e v e l h u b c o n n e c t s S a n Francisco with the Bay Area counties through 10 transit systems and will be a station for Califor nia High- Speed Rail. As part of this visionary, $6 billon project that is transforming downtown San Francisco and the Bay Area regional transportation system, a new 1849.0-ft-long Transbay bus ramp bridge system was built to provide bus transit access to the STC from the East Bay via the San Francisco–Oakland Bay Bridge exit ramp. The Transbay Ramp Bridge is the first vehicular cable-stayed bridge built in California. Urban Congestion and Seismic Risks T h e S T C i s l o c a t e d i n a d e n s e l y populated area surrounded by high- rise buildings. The bus ramp bridge connects to the second floor of the STC multilevel building and spans over a multistory underground structure composed of a local street roof, a vehicle/bicycle ramp at the first below- grade level, a concourse at the next level, and the future California High- Speed Rail underground station at the lowest level. This configuration severely limited the location of the bridge piers and foundations. The high seismicity in the Bay Area also posed design challenges. The bridge piers and foundations were located outside of the STC structural footprint to avoid dynamic seismic interactions between the STC underground structure and the bridge and to eliminate any interference between the bridge and STC structure and foundations. For the connection between the viaduct and the STC, a cantilever cable-stayed bridge was determined to be the best design option in terms of costs and aesthetics. With this configuration, large columns and foundations for the bridge in the STC underground structure were eliminated, and the seismic behavior and design of the bridge were greatly simplified. This article discusses the design of the cable-stayed bridge portion of the bus ramp bridge system. Aesthetic Compatibility with the STC Project leaders wanted the bus ramp bridge to have an aesthetic design that would complement the perforated steel, profile SALESFORCE TRANSIT CENTER BUS RAMP BRIDGE / SAN FRANCISCO, CALIFORNIA BRIDGE DESIGN ENGINEER: Arup, San Francisco, Calif. CONSTRUCTION ENGINEER: OPAC Consulting Engineers Inc., San Francisco, Calif. PRIME CONTRACTOR: Shimmick Construction, Oakland, Calif. STAY-CABLE CONTRACTOR: VSL/Structural Technologies, Fort Worth, Tex. POST-TENSIONING CONTRACTOR: Schwager Davis Inc., San Jose, Calif. SALESFORCE TRANSIT CENTER BUS RAMP BRIDGE by Qiyu Liu, Arup Aerial view of Salesforce Transit Center (STC) and the cable-stayed bridge that connects the second level of the STC to the viaduct-style bus ramp bridge system leading to the East Bay. Photo: Steve Proehl.. 12 | ASPIRE Summer 2019 P R O J E C T

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