Pushover analysis for seismic assessment of RC Nišava Bridge

Abstract

Contemporary structural design implies nonlinear behavior of ductile members for design seismic action. Therefore, the application of nonlinear analysis in the aseismic design of structures is required. Nonlinear static (pushover) analysis has become a very popular tool for the seismic assessment of structural performance during a particular earthquake due to the lower computational cost and less time consuming in comparison to the nonlinear time-history analysis. The standard pushover analysis (SPA) has been extended to the modal pushover analysis (MPA) of buildings in order to consider higher modes effects. Since the higher modes usually play an important role in the seismic bridge analysis, the MPA has been adopted for the seismic assessment of bridges. In the paper, the MPA of the Nišava Bridge structure (233.2m long 7-span continuous bridge, curved in plan with R=540m and prestressed 13.75m wide bridge deck) has been performed in transverse direction, for two levels of excitation which are 2 and 3 times higher than the design level (a g =0.1g). For the horizontal component of the seismic action, elastic response spectrum, Type 2 for soil type B, according to EN1998-1 has been selected. Analyses considering different levels of excitation and different monitoring points are carried out using the SAP2000 commercial software package. The seismic demands of the structure (peak displacements of the deck in transverse direction), subjected to the monotonically increasing lateral forces have been calculated, considering five dominant transverse modes. Hinge distribution within the structure has been determined, too, for the target displacement obtained from the MPA. The overall performance of the bridge was very satisfactory. Neither local nor global failure was predicted, even under seismic actions that three times exceed the design level. The performed analysis showed that the fundamental transverse mode shape contributes to the final response significantly. The influence of higher modes is more pronounced for higher level of excitation.