Development of Fragility Curves for Existing Residential Steel Buildings with Concentrically Braced Frames

The objective of this study is to develop analytical fragility curves for an ensemble of 3- to 6-story existing residential steel buildings with concentrically braced frames in two directions, designed during 2010 and 2015, and located in Qazvin, Iran. The buildings are modeled three-dimensionally in the OpenSees, considering braces buckling behavior. Maximum interstory drift ratio ( ) and spectral acceleration at fundamental period of the structure with 5% viscous damping ( ) are considered as Damage index ( ) and Intensity measure ( ), respectively. Limit states are specified as discussed in FEMA 356. Ground motion record selection and uncertainties assessment is carried out based on FEMA P695 methodology. Analysis is performed using truncated incremental dynamic analysis ( ). Fragility function is defined as a log-normal cumulative distribution function ( ) and maximum likelihood method is used to estimate fragility parameters. According to the fragility curves obtained, seismic vulnerability of the structures is generally increased as the number of stories rises. Concentration of the inelasticity is also found to be mainly at the first story level. The results also confirm the fact that the record to record variability is the main source of uncertainty in structural probabilistic evaluation.