Seismic demand variability of RC buildings accounting for the number of ground motions and the angle of seismic incidence

Abstract

According to Eurocode 8, nonlinear time history analyses can be performed using a group of 7 ground motions, applied using only one angle of incidence (ASI). Under these conditions, the mean value of the response under consideration can be used to represent seismic demand. Since it is known that, the smaller the group of ground motions, the larger the variability of the seismic demand, the variability of selected demand parameters is studied considering the effect of the number of bi-directional ground motions and the number of ASIs. Groups of ground motions of size 7 to 35 are involved in this analysis, all applied along 1 to 12 ASIs. Two demand parameters are examined and their variability is analysed in terms of acceptable risk, where risk corresponds to the probability of having a demand parameter outside preselected acceptable margins, which are defined with respect to a reference demand value. The results indicate that different demand parameters are influenced differently by the ground motion group size and the number of ASIs. Finally, it is demonstrated that an optimum combination of number of ground motions and ASIs can be selected depending on the acceptable margin that is selected.