UCSD Jacobs School of Engineering University of California San Diego
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Jacobs School faculty honored for contributions
New San Francisco Bay Bridge

Jacobs School structural engineers led the seismic proof testing for the new San Francisco-Oakland Bay Bridge East Span. Dynamic large-scale tests on shear links, the bridge deck, skyway piers and W2 piers were all conducted in the Powell Structural Research Laboratories.

Frieder Seible
Chia-Ming Uang
Cole McDaniel
The American Society of Civil Engineers (ASCE) recently honored dean Frieder Seible, structural engineering professor Chia- Ming Uang, and Washington University professor Cole McDaniel (Ph.D., UCSD 2002) with the 2004 Leon S. Moisseiff Award for their co-authored paper titled, "Cyclic Testing of Built-Up Steel Shear Links for the New Bay Bridge." The paper, published in the June 2003 issue of the ASCE Journal of Structural Engineering, describes research to improve welding details on a new self-anchored suspension bridge, which will replace the San Francisco-Oakland Bay Bridge East Span that was damaged during the 1989 Loma Prieta earthquake.

In 2001, the Jacobs School tested key structural elements in the main tower that supports the 1,850-ft long suspension bridge. The design of the tower was based on concepts developed at UCSD by Seible, principal investigator for all large-scale testing in direct support of this seismic safety project for Caltrans.

According to Seible, "this innovative, self-anchored suspension design includes a steel single-tower suspension span over the shipping channel near Yerba Buena Island, and a concrete pier-supported 'skyway' from the suspension span to Oakland. The suspension span's single-tower and self-anchoring features represent important advances in bridge and seismic design."

The new bridge is intended to withstand earthquakes in excess of those expected from the San Andreas and Hayward faults. The steel tower is comprised of four separate hollow shafts, interconnected by a series of horizontal links. These links, measuring 6.6 to 9.8 ft. long and 3.3 ft. deep, stiffen the tower such that it will not sway excessively in a major earthquake. "More importantly, the links are like 'structural fuses' that are made to dissipate energy in a seismic event," said Uang. After a large earthquake, the damaged links would be quickly replaced without significant delays or repairs to the overall structure.

Links of such large size that require heavy welding have never been attempted for bridge applications. Large-scale testing of links conducted at UCSD revealed some unexpected and previously unobserved brittle failure of welded connections. The paper describes measures proposed by the research team to avoid this issue. According to Uang, "we've recommended that vertical welds connecting the stiffeners to the link web be distanced from the highly restrained region by at least three times the web thickness. We also recommended that the ends of the welds be tapered to provide a smooth profile."

Construction on the Bay Bridge East Span began in 2002 and is expected to be completed in 2007.