Response Surface with random factors for seismic fragility of reinforced concrete frames

Seismic fragility curves for reinforced concrete (RC) frame structures are evaluated considering the uncertainties in both structural parameters and seismic excitation. Response Surface (RS) models with random block effects are used to solve the problem in an approximate way with good computational efficiency. The RS models are calibrated through numerical data obtained by non-linear incremental dynamic analyses performed using different sets of ground-motions, strength distributions in frame elements, and values of the random variables adopted to describe the uncertainties in the structural behaviour. The present work is mainly focused on the problem of obtaining a reasonable compromise between result soundness and computational effort. With reference to a three storey frame structure, a series of numerical tests is presented. Different simulation plans, defined following the theory of Design of Experiments (DOE), and simplified polynomial RS models are employed. The fragility curves obtained by different methods are compared, using the results from full Monte Carlo simulation as the reference solution.