On the quantification of collapse margin of a retrofitted university building in Beirut using a probabilistic approach

Abstract

The scope of this study is to investigate the feasibility and performance of several retrofitting techniques on an existing building in Beirut Arab University (BAU). The implemented retrofitting techniques were adding RC shear walls (SW) and steel bracing systems. Simulation and analysis procedures were performed in a nonlinear platform. Models are designed based on ACI 318-14 and ANSI/AISC 360-10 for concrete and steel, respectively. Non-linear time history analysis (NL-THA), non-linear static analysis (NL-SA) and collapse margin ratio are carried out to evaluate the performance of existing and retrofitted structures. Incremental dynamic analysis (IDA) curves are then generated and used to develop the seismic fragility curves. Three different strong ground motions are used in the analyses by referring to the UBC 1997 requirement. The IDA curves are compared based on five performance levels; operational phase (OP), immediate occupancy (IO), damage control (DC), life safety (LS), and collapse prevention (CP). The fragility curves and the calculated CMRs indicated that the shear wall and steel bracing systems both provide good seismic improvement and are able to achieve strengthening solution targets for an existing building system; however, the performance of RC-SW system under seismic excitation was much better. To this, RC-SW is considered as the most appropriate technique for retrofitting the main building of Beirut Arab University.