Non Linear Dynamic Response Variation under Different Sets of Earthquakes

Abstract eng:
The paper deals with the effects of different seismic input on systems structural response, considering the variability of the input on dynamic non linear analyses performed according to Eurocode 8 (EC8) rules. A comparison between the systems response under six sets of accelerograms is reported in the paper. Every set is made of 7 earthquakes (both the horizontal components are considered), fully satisfying the EC8 provisions. SDOF systems and a space frame (MDOF) are analysed. The results concerning the former systems are provided in terms of variation of strength reduction factors and ductility; they are compared to results obtained on corresponding elastic systems (elastic spectrum variation). The analyses are extended to a reinforced concrete multi-storey space frame, which is designed according to Eurocode 2 (EC2) and EC8 provisions. Results in terms of frame top displacements, interstorey drifts and chord rotations at element ends, as well as in terms of variation coefficients of these parameters, are discussed. It is shown that the EC8 provisions concerning the selection of the seismic input sets (the main condition to be satisfied by the set is that the average elastic spectrum does not underestimate the code’s spectrum, with a 10% tolerance, in a broad range of periods depending on the structure’s dynamic properties) are not completely effective, because they do not take into account the variability of the elastic spectra, which largely conditions the non linear response of structures.

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