HAZARD ASSESSMENT AND SEISMIC ACTIONS

In the paper, the definitions of the design seismic actions for different limit states and importance classes given by Eurocode 8 and by Italian construction code are analyzed. To set the context of the discussion, a brief review of the most common way to assess the seismic hazard and the parameters used to represent the hazard (essentially soil acceleration, ag, related to a fixed return period, or, that is the same, to a fixed probability of exceedance in a given time) is done. Then, the problems involved in the way to assess the seismic actions in the European and Italian codes are highlighted: first, the definition of a fixed factor to obtain the ag for the damage limit state, starting from the ag with 10% probability of exceedance in 50 years; second, the definition of fixed importance factors applied to the ag depending on the different importance classes. A comparison among the seismic actions obtained by the use of fixed factors and by the calculation of the values of ag relative to different return periods, for the Italian municipalities, has been done. The results show a great difference among the values obtained, particularly it’s possible to observe a great variability of the ratio calculated among the ag relative to different return periods.