Geographic information systems for ground motion evaluation in seismic bridge analysis

Abstract

Public safety requires that bridges be designed for the entire spectrum of loading conditions that could result in failures. During the past decade, seismic bridge design has become oriented towards specific performance objectives by considering possible rates of earthquake occurrence over the design life of the structure. A geographic information system (GIS) methodology for establishing potential long-term seismic risk for bridges is described in this paper. The GIS graphical and computational capabilities to analyze spatially distributed problems are shown to be an ideal, powerful tool for establishing ground motions within the performance-based criteria of modern seismic bridge design. Sample outputs for the Eastern United States (EUS) are presented as an application. Seismic events in this area are infrequent; however, they can pose a serious threat, especially considering that many of the bridges in EUS were built before seismic design was required. There are many problems associated in determining ground motions in the EUS, including a scarcity of recorded data, incomplete knowledge of seismic wave propagation characteristics, and sometimes insufficient knowledge of geologic conditions. In spite of these difficulties, it is possible to arrive at a rational estimate of the seismic risk potential in a probabilistic manner, combining available information, assumptions, and uncertainties using a GIS environment.