Near-fault effects on the seismic demand of RC buildings in linear and nonlinear analyses

Abstract

Strong ground motions of near-fault earthquakes are mostly generated by forward-directivity effects. Forward-directivity effects develop energetic pulses, particularly in the horizontal velocity history of the fault-normal component. The narrow-band nature of the pulses results in the occurrence of at least two peaks on the response spectra as well as increase in seismic demand, especially in mid-rise and high-rise buildings. Iranian seismic code (IS 2800-14) presents the coefficient N for considering near-fault effects. It seems that N is not efficient for designing in near-fault zone. The accurate near-fault demands can be determined by using nonlinear response history analyses. In the present paper, two 3-D reinforced concrete framed structures (RC buildings) are designed according to ACI 2014 and IS 2800-14. Then, the demands are estimated by employing Linear Response History Analysis (LRHA) and Nonlinear Response History Analysis (NRHA) under an ensemble of 11 near-fault ground motions. The results reveal that the design spectrum of IS 2800-14 is incompatible with near-fault spectra and underestimates demands in the long periods range. Further, implementation of LRHA using response modification factor (Ru) and deflection amplification factor (Cd) leads to insufficient inter-story drift ratios. Finally, the influence of enhancing ductility is studied by determining ductility reduction factors for near-fault records.