Seismic Response Estimation and Fragility Curve Development Using an Innovative Response Bound Method

Abstract

Incremental dynamic analysis (IDA) is one of the widely used methods for structural assessment analysis and fragility curve development, given its unique capabilities in taking into account the aleatory uncertainties of earthquake records and its ability to provide a desirable statistical population of the system response. However, the strong dependence of the results on the number of selected records, the record selection process and scaling procedure, as well as the associated high computational costs are some of the obstacles, which limit the practicality of the IDA method especially in the case of large-scale structures. In the present study, an alternative approach called “Response Bounds” is proposed to estimate the expected range of structural responses under earthquakes with different intensity levels and to develop seismic fragility curves. To reduce computational costs and address the challenges associated with the record selection, a novel scenario-based Endurance Time (ET) analysis method is adopted. The good agreement between the fragility results of 5-, 10-, and 15-storey steel moment-resisting frames obtained by the proposed method and the IDA (less than 9% error) demonstrated the accuracy and reliability of the predicted results. The method could also estimate the mean loss ratio from fragility curves with less than 5% error in all cases. The proposed response-bound method can significantly reduce the computational costs of conventional seismic fragility assessment methods, and therefore can be used as an efficient tool for seismic reliability analysis in practical applications.