Generalized force vectors for multi-mode pushover analysis of bridges

Abstract

Nonlinear static procedures (NSPs) are gaining wider use in performance based earthquake engineering practice due to their simplicity compared to rigorous nonlinear time history analysis (NTHA), and being implemented in the new generation of seismic design codes. In this study, a recently proposed Nonlinear Static Procedure (NSP) for the seismic performance assessment of building structures using the concept of generalized force vectors (GFV), is further validated through application to reinforced concrete bridges. This method, named generalized pushover analysis (GPA), maximizes the response of a chosen parameter during the seismic response, through the use of the GFV, which are a combination of modal forces representing the instantaneous force acting on the system when such parameter reaches its maximum. In this study, the original GPA implemented in buildings is adapted to bridge structures and four versions of the algorithm are tested. Two straight bridges, featuring different levels of vertical irregularity, are used as case study to validate the procedure, and the accuracy of the GPA algorithm is assessed by comparing the nonlinear static results with the “exact” prediction from NTHA. Several levels of seismic hazard, represented in the expected return period of the target spectra, are considered to test the accuracy of the method for low and high seismic demand. Furthermore, the GPA results are also compared with a commonly employed NSP, the capacity spectrum method. The results obtained for the case study suggest that GPA algorithm for bridges is suitable as a NSP approach for the seismic assessment of bridge structures, demonstrating a good fit with NTHA results and superiority with respect to the predictions of the selected traditional NSP.