Abstract

Time-history analysis is the most reliable method for the assessment of the behaviour of bridges subjected to seismic loads. It has been widely used in recent years on the evaluation of the seismic vulnerability of bridges. The selection of seismic motions is one of the most important issues for the time-history analysis. This thesis discusses four different methods for obtaining spectrum-compatible acceleration time histories (i.e., accelerograms) of seismic motions. Based on these methods, four sets of accelerograms compatible with the design spectrum for Montreal were selected for this study. These included (i) scaled real accelerograms, (ii) modified real accelerograms, (iii) simulated accelerograms, and (iv) artificial accelerograms. The selected sets were used as excitation motions in the nonlinear analysis of two existing bridges in Montreal. The bridges included a three-span continuous concrete slab bridge and a three-span continuous slab-girder type bridge. These two bridges are considered to be representative of typical highway bridges in Quebec. A number of response parameters, such as, the deck displacement, bearing displacement, column curvature ductility, and base shear were used for the evaluation of the effects of the selected sets on the response of the bridges. Based on the results from the analysis, simulated accelerograms are recommended for use in the time-history analysis of the bridges. Furthermore, a study was conducted on the investigation of the minimum number of accelerograms required for both linear and nonlinear time-history analyses. Two different scaling methods, i.e., partial area under the spectrum and the spectral acceleration at the fundamental period of the bridge, were used to obtain the bridge responses. It was found that 5 accelerograms are sufficient for the linear time-history analysis and 10 accelerograms are required for the nonlinear time-history analysis based on the results from the two bridges considered in this study.