Investigating the use of record-to-record variability in static capacity approaches

In performance-based earthquake engineering, fragility curves constitute an essential component, providing a probabilistic link between the earthquake intensity measure and the structural response, expressed as an engineering demand parameter. In this study, we apply a capacity spectrum method that uses inelastic response spectra derived from earthquake accelerograms to construct fragility curves for an example reinforced concrete structure. This approach has the advantage of simplicity and rapidity over methods using the accelerograms directly. Various sets of scaled and unscaled accelerograms are used to investigate the impact of record-to-record variability on the derived curves. It is found that the variability in the input spectra at periods longer than the natural period of the undamaged structure has a direct impact on the standard deviation associated with the curves. When the spectra closely match a target, the curves are almost vertical (small standard deviations); but, as the variation around the target increases ,the curves become flatter (high standard deviations). A variant of the peak-to-trough measure introduced by Stafford and Bommer (2010) provides a useful way of measuring the variability in the input spectra.