Identification of incremental seismic damage development in RC structures excited with sequence-type ground motions

Aftershocks usually come after a mainshock. However, controversy of the impact of aftershocks on structures arises in previous studies. To further interpret the effect of sequence-type ground motions on reinforced concrete (RC) structures, an incremental seismic damage (ISD) model is proposed based on the modified Park-Ang model. Based on the ISD model, an attempt is made to identify the coupling mechanism between ISD and recorded peak response, the transition in periods and the characteristics of sequence-type ground motions. The analogous resonance-type aftershocks defined herein provides some assistance in addressing such mechanism. Smaller post-yielding stiffness implies more sensitivity of damage to excitations with long periods. The mean period of a sequence-type motion is found to have a distinct impact on the global damage development tendency. The coupling effect on ISD development is comprehensively investigated by several single-degree-of-freedom systems and two RC frames. A mainshock-induced damage tolerance or "threshold" is observed, implying no obvious ISD is developed unless a significant increment in recorded peak response is caused. The reduced earthquake resistance reserve caused by mainshocks is not always consistent with ISD development.