RESILIENCE ASSESSMENT OF A BUILDING CONSIDERING THE EFFECTS OF AFTERSHOCKS

The massive economic losses induced by earthquakes have long-term and serious impacts on the economic and social development. For improving the overall earthquake prevention and mitigation capabilities, system seismic resilience has become the research highlight in earthquake engineering which includes the damage assessment, government responses and recovery process. However, few studies focused on the effect mainshock-aftershock (MSAS) sequences on the seismic resilience of systems. Aftershocks usually follow the mainshock of an earthquake and have the potential to induce additional damage in the mainshock-damaged structures. Besides, the occurring of aftershocks would significantly affect the repair and recovery of a damaged structure, and thus further affect the resilience of a structure. This paper intends to assess the seismic resilience of a building considering the effects of aftershocks. The recovery time and pre-event functionality are introduced in the definition of the resilience loss factor which make it concentrate more on the intrinsic characteristics of structures during the recovery process. A reinforced concrete (RC) frame structure designed according to the current Chinese seismic code is demonstrated for the evaluation of resilience loss incorporating MSAS sequences. The structure is modeled with the OpenSees where columns and beams are simulated by the displacement-based beam-column elements with nonlinear fiber section. Then, increment dynamic analysis is applied to obtain the seismic demand of structure and maximum inter-story drift ratio (MIDR) is utilized to quantify the damage of this structure under MSAS sequences. The spectral acceleration (Sa) of mainshock ground motion is scaled from 0.1 g to 1.2 g, and relative intensity of the corresponding aftershock ground motion (i.e., ratio of the aftershock Sa to the mainshock Sa) is scaled to 0.5, 0.8 and 1.0 respectively. The cost of this building is computed based on the construction project cost information provided by the department of housing and urban-rural development of China. The economic losses induced by MSAS sequences are assessed by the damage extent and the loss ratios of various damage states provided by the code of the earthquake field work. The numerical results of case study illustrate that replacement threshold and aftershocks have a significant effect on resilience loss. The resilience loss of structure can exceed 200% and 400% considering replacement threshold and aftershocks respectively. The proposed resilience loss factor can be used to design a new structure by controlling the level of resilience loss and assess the seismic resilience of a building considering the effect of replacement threshold and aftershocks.