Seismic performance of steel concrete composite structures: a fragility analysis

In this paper the nonlinear monotonic behavior of a composite (steel-concrete) structure has been modeled on the base of experimental data. The evaluation of the seismic response has been performed by applying spectral analysis based on inelastic spectra and performance curves evaluated by pushover analysis with a uniform pattern and with first mode shape pattern of horizontal forces. An ensemble of twenty earthquake records, representing the seismic action as provided by Eurocode 8 for soil type A, has been considered as input ground motion. The obtained response domains, assumed to have a gaussian distribution, have been compared with the limit states provided by the SEAOC Blue Book. The probability of exceeding the assumed limit states have been expressed in terms of fragility curves. The examination of the obtained fragility curves underlines that the general limit values considered for framed structures appear not to be fully satisfactory to define performance levels of composite structures.