Seismic Damage State Models for Oregon Bridges

Peter Dusicka, Portland State University


The U.S. highway transportation network relies on the health and integrity of major infrastructure elements such as bridges. Frequently traveled parts of Oregon are within the seismically active Pacific Northwest, and many of the bridges were designed and built to lateral demands that were assumed to be less than the current expectation, a deficiency caused by our growing awareness of seismic hazard and our enhanced understanding of the non-linear response of bridges. This vulnerability to damage from earthquakes can result in not only immediate damage, but also in potentially lingering economic impacts caused by the disruption to traffic and freight mobility. One of the key components in determining the impact of an earthquake on the transportation network is the bridge damage state model represented by fragility curves. A bridge fragility curve provides the probability that a bridge is damaged beyond a specified damage state under various levels of ground movement. Several methods of producing fragility curves were considered, specifically curves based upon actual failure data, expert opinion, and analytical models derived from the physics of the actual bridge system. Using analytical methods, fragility curves were constructed using the calculated median value and dispersion (standard deviation) values of the lognormal capacity distributions for the four damage-state conditions of slight, moderate, extensive, and complete levels of damage. These statistical values were compared to the median and dispersion values proposed by other researchers, in addition to those calculated using guidelines from the HAZUS Technical Manual. As a result of this modeling and analysis effort, the relative fragility of the modeled typical threespan and five-span bridges was determined and quantified. Possible causes of the relatively high fragilities were also considered.

Project Details

Project Type:
Project Status:
End Date:
February 28,2009
UTC Grant Cycle:
OTREC 2008
UTC Funding: