Seismic fragility comparison of FBD and DDBD designed RC frame using incremental dynamic analysis

Abstract

Abstract Direct displacement-based design (DDBD) is a design approach in which structures are designed for predefined displacements to withstand earthquakes within specified performance criteria. In order to defeat the drawbacks of force-based design (FBD), which is based on stiffness assumptions, the DDBD method evaluated the displacement constraint in which structure response must remain within the predetermined displacement. The fragility assessment reveals the structure’s probability of future collapse from the nonlinear analysis will help to detect the structure’s performance. In this study, Incremental dynamic analysis (IDA) is performed on a four-story reinforced concrete (RC) frame structure designed using DDBD and FBD approach to predict nonlinear structural behavior in earthquake-prone regions. The RC frame is designed to satisfy the immediate occupancy (IO) performance limit of 1% drift while taking into account the DDBD method. Sixteen ground motions with two horizontal directions mounted to various intensity levels represented by peak ground acceleration (PGA) are used to perform IDA. Fragility curves are generated from logarithms of intensity measures (IM) computed from the IDA. As a result, earthquake damage in terms of the probability of collapse and inter-storey drift ratio are compared for both approaches and using the DDBD approach, four times less PGA occurrence is observed for the IO performance limit compared to FBD.