Performance Based Seismic Evaluation of Low to Mid Rise RC Building Under Sequential Earthquakes

Abstract

In design practice, seismic design of buildings is carried out considering single site specific earthquake, assuming an initially undamaged building condition. However, in real time scenario, earthquakes occur in sequence causing accumulative damage to affected structures. This damage accumulation in structural systems increases level of degradation in stiffness and strength. Present code based design provisions lacks the damage accumulation features to account for stiffness and strength degradation resulting from repeated earthquake loading. On the other hand, existing Seismic design codes are based on the elastic structural behavior and nonlinearity in behavior is incorporated indirectly through coefficients given is design code e.g. response modification factor, R. Therefore, the structures designed on this basis may experience undesirable inelastic deformation during severe earthquakes. Since Pakistan is located in seismically active region; therefore, response of existing buildings conforming building code of Pakistan 2007 (BCP 2007) needs immediate re-evaluation considering Mainshock-aftershock. The objective of this study is to conduct detailed nonlinear seismic performance assessment of typical low to Mid-rise RC frame structures conforming existing code of practice in Pakistan considering repeated earthquakes. For this purpose, nonlinear model has been made on FEM analysis based software (PERFORM 3D) to capture damage accumulation. The seismic performance of one real building along with generalized structures is evaluated in terms of key engineering demand parameters inter-story drift, displacement time history and inelastic dissipated energy at structural level. The performance at component level is evaluated in terms of concrete compression strains and steel yielding. This seismic evaluation is performed for single-earthquake and multiple- earthquake scenarios. Earthquakes are selected considering ground motion parameters for Islamabad. These ground motions are further scaled to two hazard levels namely, DBE and MCE. Evaluation of results for response against mainshock-aftershock sequences show that IDR, Inelastic dissipated energy and damage at component level increases with increase in building height but this impact is sensitive to selection of earthquake time histories. Keywords: Repeated Earthquakes, Aftershocks, Pakistan, Mid-rise RC Buildings, Nonlinear time history analysis