Seismic analysis of bridges using nonlinear static procedure

Performance-based seismic analysis and rehabilitation of structures is recognized as an efficient approach and it is expected to be part of code requirements in the near future. Such an approach requires an efficient and practical procedure to perform analysis. Nonlinear Static (Pushover) Procedure (NSP) is specified by FEMA-273 (1997) as an analytical procedure that can be used in systematic rehabilitation of structures. However, guidelines presented in FEMA-273 apply the Displacement Coefficient Method (DCM), but only for buildings. Capacity Spectrum Method (CSM), that was developed by the Applied Technology Council, also applies the NSP only for buildings. This study is intended to evaluate the applicability of NSP by implementing the DCM and CSM to bridges. Some modifications that would render the DCM applicable for bridges are proposed in this study. For comparison purposes, the Nonlinear Dynamic Procedure (NDP) (or nonlinear time-history analysis), which is considered to be the most accurate and reliable method of nonlinear seismic analysis, is also performed.; Three bridges were analyzed using both the NSP and NDP. A fourth bridge, which experienced some damage due to Taiwan Chi-Chi earthquake in 1999, was analyzed using the NSP to evaluate its applicability to predict damage. 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 NSP are compared with the corresponding values resulting from the NDP. Comparison shows a good agreement in general between the results of the NSP and NDP. When a structure is driven far into the inelastic range, the differences between the two procedures increases and the DCM gives conservative results while the CSM may underestimate the base shear. It can be concluded that the DCM is more applicable, in general, for bridges considering the modifications made in this study. CSM is also applicable for bridges, with some shortcomings associated with the method in general, even when it is applied for buildings. These shortcomings are considered as areas for further research to build more confidence in the NSP.