Damage demands evaluation of reinforced concrete frame structure subjected to near-fault seismic sequences

The design earthquake is usually specified as a single event in most of modern seismic codes. However, one earthquake is often followed by a series of aftershocks called seismic sequence. Such cases are quite common, especially in near-fault regions, which could cause additional accumulated damage to structures. In this paper, a new methodology for evaluating the effect of near-fault seismic sequences on the accumulated damage of reinforced concrete (RC) frame structure is proposed, in which different initial damage levels (i.e., postmainshock global damage index) of structure after the mainshock are considered. Meanwhile, a quantitative description of the damage demands and the relative intensity index between mainshock and aftershock are provided. For this purpose, the nonlinear dynamic response of an eight-story RC frame structure subjected to single earthquake and seismic sequence is compared in terms of structural performance indices (collapse capacity, story damage demands, postmainshock damage level and normalized hysteretic energy) and relative intensity index. The results indicated that seismic sequences lead to reduced collapse capacity of postmainshock-damaged structures. Moreover, the near-fault pulse-like aftershock records would induce larger structural story damage demands than ordinary (i.e., non-pulse-like) aftershock records. Furthermore, the relative intensity index proposed in this paper has significant effects on the structural story damage demands, incremental dynamic analysis curves of aftershock and normalized hysteretic energy.