COMPARATIVE STUDY OF SEISMIC DESIGN METHODS FOR RC BRIDGES

Abstract

Force Based Design (FBD) methodology mainly focuses on target strength. This method employs elastic analysis and inelastic response is considered by using response reduction factors. Special ductile detailing is used at plastic hinge location to ensure ductile behavior of structure. Forced based design methodology is used in many codes but there are many fundamental problems associated with the procedure. The main issue with the FBD is that stiffness of the member is considered to be independent of the strength of the member. FBD method cannot be related to the true performance of the bridges, due to the uncertainties that are present while considering the expected performance. Most of the deficiencies that were inherent in the FBD were rectified in the Performance Based Design (PBD) approach. PBD approach allows attaining the target performance levels explicitly. Using the lateral drifts, curvature, displacements, rotations, ductility and strains the performance levels can be found out. Also, PBD can give the performance for a range of hazards as compared to current seismic codes where single hazard can be obtained .In this study an attempt has been made to compare performance from PBD and FBD methodologies. Performance parameter for FBD is response modification factor and for PBD it may be displacement and ductility. Two bridge piers of different heights are taken for this study and both are designed using FBD and PBD. Various analyses are performed to evaluate performance of these methods. Incremental dynamic analysis and pushover analysis are performed to calculate maximum displacement, ductility, response modification factor and spectral acceleration. Finally, fragility analysis is carried out to measure collapse probability.