Performance Evaluation of the Damaged Steel Moment Frames under Mainshock-Aftershock Sequences Considering Plastic Hinge Modification Factors

With the aim of providing a tool for comprehensive seismic analyses of damaged steel moment resisting frames, this paper presents the development of a structural model that is able to describe the general behavior of damaged steel structures under repeated earthquakes. A regular 3D special steel moment frame designed using AISC 360-10 have been modeled to evaluate the effects of mainshockaftershock sequences on seismic behavior of structures. At first, rotations of each plastic hinge of the structure were determined under a set of records by the nonlinear dynamic analysis. Next, based on the deformation of hinges under main-shocks, suitable damaged hinges were assigned to each hinge. At last, again, the nonlinear time history analyses were carried out to evaluate the performance of damaged steel moment frame structures under repeated earthquakes. It seems that the effects of cumulative damage in Damaged Modified Method did not trigger special floors. The results have shown the importance of considering the effects of mainshock-aftershock sequences in design codes. Finally, the response of the structure computed by Damaged Modified Hinges method was compared with repeated method that is common in evaluation and vulnerability of structures under seismic sequences. Besides, it is shown that considering the initial damage in element behaviors could change the structural mechanism.