Aftershock Collapse Fragility Of RC Frames Considering Mainshock Damage Scenarios And Aftershock Spectral Shapes

Historical earthquake events indicate that a major earthquake is usually followed by a number of aftershocks.For a specific building suffering mainshock-induced damages,its collapse likelihood will be significantly increased.However,the aftershock collapse capcity of the mainshock-damaged structure has not been sufficiently considered in the current design provisions and the related studies.Therefore a four-story and an eight-story reinforced concrete(RC)frame are used to investigate the effects of different mainshock-induced damage scenarios and aftershock spectral shapes on aftershock collapse fragility.The main contents of this thesis are summarized as follows:(1)Study on the influence of the number and intensity of aftershocks on the seismic response of RC frames.Maximum interstory drift,maximum roof displacement and modified Park-Ang damage index are used as the structural response parameters.A set of mainshock-aftershock sequences including multiple aftershock records is selected as the inputs of mainshock-aftershock sequences.As a comparison,for an earthquake sequence with multiple aftershocks,only the aftershock with the maximum magnitude is used to generate another earthquake sequence with one aftershock.The effects of multiple aftershocks on structural damages are then examined by comparing the structural responses due to mainshock-aftershock sequences with one and multiple aftershock records.Further more,the relationship between aftershock intensities in terms of peak ground acceleration(PGA)and Arias intensity and incremental damages of structures due to aftershocks is developed and preliminary results are provided to investigate the effect of aftershock intensities on incremental damages of structures.(2)Conducting aftershock collapse fragility analysis of RC frames considering mainshock damage scenarios.Three approaches which include Pushover analysis,single dynamic analysis and multiple dynamic analysis are used to simulate mainshock-induced damage scenarios.Then the mainshock-induced damages of different levels are initialized on a structure by the above three approaches to generate collapse fragility for the mainshock-damaged structure.The effects of different mainshock-induced damage scenarios on aftershock collapse fragility are investigated by comparing the aftershock collapse fragility results corresponding to different mainshock damage scenarios.(3)Conducting aftershock collapse fragility analysis of RC frames considering aftershock spectral shapes.The calculated aftershock collapse fragility results were first classified according to the values of aftershock spectral shapes in order to examine the influence of aftershock spectral shapes on aftershock collapse fragility.Moreover,the structural aftershock collapse fragility was modified using the target spectral shape values ? of ±2,±1 and 0.