Effect of Mainshock–Aftershock Excitations on Seismic Energy Dissipation Mechanism of RC Frames

Abstract

Four RC moment frames (RCMFs) with 4–20 stories are designed, modeled, and subjected to IDA procedures by considering various levels of prior damage caused by mainshock (MS). The collapse of the structures is then identified by gradual scale-up of the aftershock until dynamic instability is observed. The percentage of the energies dissipated by various parts of the structures and via different modes is next studied at three states during the collapse-inducing excitation. These states include the final residual state, the maximum drift state, and the maximum kinetic energy state. While an almost constant contribution of around 30% is provided by the inherent damping of the nodal masses, the share of beams’ hysteretic energy varies between 10% in the low-rise shear-dominated frame and 30% in the high-rise flexure-dominated RCMFs. The contribution of the columns’ hysteresis also changes in a reverse manner so that the sum of ratios provided by the beams and columns hysteresis is kept constant and equal to around 70%. The prior damage caused by the MS also leads to changes in the contribution of various elements and stories due to the deterioration MS induces to the strength of the members.