Seismic Vulnerability of Gravity-Load Designed Buildings

ABSTRACT Buildings designed primarily for gravity loads are prone to suffer shear failures in walls, columns and beams when subjected to far field effects of earthquakes. In previous studies, pushover analyses carried out on these buildings were terminated when a local shear capacity is reached. However, by considering shear yielding, ductile shear hinges can be used to model the behaviour of such buildings. By comparing the capacity determined with this new modeling feature with the seismic demand due to long distant earthquakes, the performance of a typical gravity-load designed, 25-storey building at critical soil sites in Singapore is investigated in this study. Keywords: concrete structure, ductile shear hinge, post local shear failure behavior, pushover analysis. 1. INTRODUCTION Many buildings in large Asian cities like Bangkok, Kuala Lumpur, Seoul and Singapore are designed primarily for gravity loads due to little or no local seismic activities. However, it has been realized that such gravity-load designed (GLD) buildings are not totally immune to the effects of far-field earthquakes, especially if they are sited on soft grounds that are likely to amplify the seismic waves. Research on seismic performance including capacity of GLD reinforced concrete structures has been carried out in Singapore context (Balendra et al. 1999, 2001, Kong et al. 2003). A microscopic model calibrated for shear walls has been used to determine the capacity of full scale shear wall structures (Kong 2004). Also, a macroscopic model for capacity evaluation of shear wall-frame structures was presented in Balendra et al. (2007), with which a pushover analysis of a 25-storey point block was carried out and the analysis was terminated at the onset of shear failure at the base of the shear wall. This study focused on ductile shear failure using SAP2000 (2009) software, taking advantage of its shear hinge feature to model the post elastic shear behavior