10-04-2017, 08:36 PM
SEISMIC ANALYSIS OF BRIDGES USING DISPLACEMENT-BASED APPROACH
By Chung C. Fu and Hamed AlAyed, University of Maryland
ABSTRACT
Nonlinear Static (Pushover) Procedure is specified in the guidelines for seismic rehabilitation of buildings presented by FEMA-273 (1997) as an analytical procedure that can be used in systematic rehabilitation of structures. However, those guidelines were presented to apply the Displacement Coefficient Method, which implements the well-known equal displacement rule with some modifications to estimate target (demand) displacement, only for buildings. This study is intended to evaluate the applicability of Nonlinear Static Procedure by implementing the Displacement Coefficient Method to bridges. For comparison purposes, the Nonlinear Dynamic Procedure (or nonlinear time-history analysis), which is considered to be the most accurate and reliable method of nonlinear seismic analysis, is also performed. A three-span bridge of 97.5 meters (320 ft) in total length was analyzed using both the Nonlinear Static Procedure/Displacement Coefficient Method and nonlinear time-history. Nine time-histories were implemented to perform the nonlinear time-history analysis. Three load patterns were used to represent distribution of the inertia forces resulting from earthquakes. Demand (target) displacement, base shear, and deformation of plastic hinges obtained from the Nonlinear Static (Pushover) Procedure are compared with the corresponding values resulting from the nonlinear time history analysis. Analysis was performed using two levels of seismic load intensities (Design level and Maximum Considered Earthquake level). Performance of the bridge was evaluated against these two seismic loads. Comparison shows that the Nonlinear Static Procedure gives conservative results, compared to the nonlinear time history analysis, in the Design Level while it gives more conservative results in the Maximum Considered Earthquake level.
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