Seismic and Blast Protection of Bridges Seminar

• April 13, 2009: 12:00pm - 1:00pm
• Location: 502 Davis Hall, UC Berkeley

Abolhassan Astaneh-Asl, Ph.D., P.E.
Professor, Department of Civil and Environmental Engineering
University of California, Berkeley

Abstract:
During the 1989, Loma Prieta, the 1994 Northridge and the 1995 Kobe earthquakes a number of major long span suspension and cable stayed bridges, including the San Francisco Oakland Bay Bridge and the Akashi-Kaikyo Bridge, were subjected to strong ground motions and several were damaged. After discussing performance of long span bridges during past earthquakes and lessons learned from them, the results of a collaborative UCB and LLNL research project studying dynamic behavior of steel suspension bridges will be presented. The studies indicated that these long period structures are quite sensitive to long period motions and near fault permanent deformations. The case of dynamic response of the western crossing of the San Francisco Oakland Bay Bridge will be discussed and presented as an example of effects of long period motions on the response. The presentation will discuss how the findings can be applied in seismic analysis and design of long span bridges to enhance their performance and minimize seismic damage.
The second part of this seminar is on the response of long span suspension and cable-stayed bridges subjected to blast loads and measures to protect them against progressive and catastrophic collapse. The three types of long span cable-supported bridges studied were (a) typical suspension bridges, such as the west spans of the Bay Bridge, where the main cables are anchored to the anchor blocks and the ground, (b) the self-anchored suspension bridges, such as the new East Spans of the Bay bridge currently under construction, where the cables are attached to the deck of the bridge instead of the ground, and (c) typical cable stayed bridges where there is no main cable and the stay-cables are directly connected to the deck of the bridge. We found that the main parameters affecting the response of these bridges to blast are the material properties and the amount of axial compressive force present in the deck in the longitudinal direction of the bridge. The typical suspension bridge anchored to the ground, which has almost zero axial force in the deck had the best performance and showed no tendency for progressive collapse. The self-anchored suspension bridge, which has very large axial compressive force, due to horizontal component of the tension force in the main cables, had the most inferior performance. The presentation will discuss innovative technologies that can be used to protect cable-supported bridges against blast effects and to prevent their progressive and catastrophic collapse.