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Title:Seismic Fragility Analysis of Highway Bridges
Author(s):Hwang, Howard; Liu, Jing Bo; Chiu, Yi-Huei
Subject(s):Mid-America Earthquake (MAE) Center
Abstract:Past earthquakes, such as the 1971 San Fernando earthquake, the 1994 Northridge earthquake, the 1995 Great Hanshin earthquake in Japan, and the 1999 Chi-Chi earthquake in Taiwan, have demonstrated that bridges are vulnerable to earthquakes. The seismic vulnerability of highway bridges is usually expressed in the form of fragility curves, which display the conditional probability that the structural demand (structural response) caused by various levels of ground shaking exceeds the structural capacity defined by a damage state. Fragility curves of structures can be generated empirically and analytically. Empirical fragility curves are usually developed based on the damage reports from past earthquakes, while analytical fragility curves are developed from seismic response analysis of structures and the resulting fragility curves are verified with actual earthquake data, if available. Since earthquake damage data are very scarce in the central and eastern United States, the analytical method is the only feasible approach to develop fragility curves for structures in this region. This report presents an analytical method for the development of fragility curves of highway bridges. In this method, uncertainties in the parameters used in modeling ground motion, site conditions, and bridges are identified and quantified to establish a set of earthquake-site-bridge samples. A nonlinear time history response analysis is performed for each earthquake-sitebridge sample to establish the probabilistic characteristics of structural demand as a function of a ground shaking parameter, for example, spectral acceleration or peak ground acceleration. Furthermore, bridge damage states are defined and the probabilistic characteristics of structural capacity corresponding to each damage state are established. Then, the conditional probabilities that structural demand exceeds structural capacity are computed and the results are displayed as fragility curves. The advantage of this approach is that the assessment of uncertainties in the modeling parameters can be easily verified and refined. To illustrate the proposed method, the method is applied to a continuous concrete bridge commonly found in the highway systems affected by the New Madrid seismic zone.
Issue Date:2001-07
Series/Report:Mid-America Earthquake Center CD Release 01-06
Sponsor:National Science Foundation EEC-9701785
Date Available in IDEALS:2008-12-08

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