Analysis of the Effect of Mainshock-Aftershock Sequences on the Fragility of RC Bridge Columns

The mainshock (MS) is often accompanied by a number of aftershocks (AS). The existence of AS may cause the seismic demand to be greater than the MS. In order to better evaluate the impact of AS, this paper takes RC columns as the research object and performs incremental dynamic analysis (IDA) on the actual recorded mainshock-aftershocks (MS-AS). The Park–Ang model and incremental damage index are used to quantify the effect of the MS and AS, respectively. The damage and fragility analysis of the parameters such as reinforcement ratio, axial compression ratio and shear-span ratio are carried out respectively. The results show that the seismic demand of the MS-AS is greater than the MS. Besides, the damage of the column gradually increases with the increase of axial compression ratio and shear-span ratio, and gradually decreases with the increase of the reinforcement ratio. When the seismic design grade is 7, 8, and 9 degree, the maximum increase rate of additional damage caused by aftershocks is 7, 13, and 15% of the MS, respectively. When the column is in a medium damaged and a severely damaged state, the growth rate of additional damage can be estimated to be 12.7 and 11% of the MS, respectively. The fragility of columns in different damage states under the action of MS-AS is greater than that of MS. Reducing the axial pressure ratio can greatly reduce the damage probability of columns in different damage states. The effect of the MS-AS can be comprehensively considered to select appropriate design parameters in the design, and the additional damage caused by the AS can be estimated according to the damage condition of the column.