Incremental dynamic analysis with multi-modes for seismic performance evaluation of RC bridges

This study aimed to investigate the seismic performance of the typical single column reinforced concrete bridges in Thailand under the earthquake intensity level of Bangkok by the mean of incremental dynamic analysis (IDA). The concept of IDA by equivalent single-degree-of-freedom system (ESDOF) was adopted to evaluate the seismic performance of the studied bridges by the charms of less computational price. The effects of two important parameters that influence the seismic behavior generated by the IDA of ESDOF, i.e. lateral load pattern and hysteresis model, were also investigated. The results show that the different load patterns result in significantly different seismic behavior, especially for the bridge with low participating mass ratio for fundamental mode, while the using of different hysteresis models show less significance. The simple standard-based load patterns can be used effectively only for the bridge which is dominated by the fundamental mode. To account for the higher mode effects, but retain the simplicity of single-run nonlinear static analysis (NSA) and nonlinear time history analysis (NTHA) of ESDOF, the multi-modes combination load pattern is proposed in this study. The distribution of load can be generated by the simple combination of considered mode shapes weighted by their modal participating mass ratios. By using the proposed load pattern, the seismic behavior evaluated by the IDA of ESDOF agree well with the results of IDA of multi-degree-of-freedom system for all studied bridges. The results also show that the studied bridges can resist the considered earthquakes without any damage.