Influence of design criteria on the seismic reliability of X-braced frames

According to the most modern trend, performance-based seismic design is aimed at the evaluation of the seismic risk defined as the mean annual frequency of exceeding a threshold of level damage, i.e. a limit state. A procedure for performance-based seismic design is herein briefly summarised and applied to concentrically “X” braced steel frames, designed according to different criteria. In particular, two design approaches are examined. The first one corresponds to the provisions suggested by Eurocode 8 (2003b), while the second approach is based on a rigorous application of capacity design criteria aiming to the control of the failure mode (Longo et al. 2005). The aim of the presented work is to focus on the seismic reliability obtained through these design methodologies. The probabilistic approach is based on an appropriate combination of probabilistic seismic hazard analysis (PSHA), probabilistic seismic demand analysis (PSDA) and probabilistic seismic capacity analysis (PSCA). Regarding PSDA, non linear dynamic analyses have been carried out in order to obtain the parameters describing the probabilistic distribution laws of demand, conditioned to given values of the earthquake intensity measure.