Assessment of Structure-Specific Fragility Curves for Soft Storey Buildings Implementing IDA and SPO Approaches

Soft storey building is popular due to the functional and aesthetic purpose, despite its weakness in resisting seismic excitation. Nonlinear Static (Pushover) Analysis (POA) is a time saving and simple assessment procedure prosposed in Eurocode 8 (EC8). However, its reliability in designing structure still remains a question. At the first stage, seismic performance of several building models using POA in EC8 is assessed. Later on, empirical accuracy of fragility curves generated by POA (using SPO2FRAG software) is studied and verified through Incremental Dynamic Analysis (IDA) results.  Four models of regular and soft storey frame of 5- and 11-storey varying heights were designed according to Eurocode 2 (EC2) and (EC8). The simulation is performed in a NL platform to carry out POA and IDA. Capacity curve obtained is served as main input in SPO2FRAG software to generate fragility curve. Then, IDA is performed to generate IDA and fragility curves. Peak ground acceleration, PGA was converted into corresponding Sa(T1) using design spectrum from EC8. Performance levels of Life Safety (LS) and Near Collapse (NC) proposed by Vision-2000 have been the main interest in this study. Results shown that the base shear calculated by using Lateral Force Method in EC8 is adequate. Fragility curve generated by SPO2FRAG, has good comformity with IDA-based fragility estimation for regular 5-storey model; however, some deviation is observed for soft storey model (5-storey). All 11-storey frames shown unsatisfactory match of fragility curves from what was generated by SPO2FRAG, compared to IDA results.