Seismic Capacity of EC8 Compliant RC Frames with Irregular Vertical Distribution of Stiffness

It is well established that structural irregularity in elevation affects the seismic response of buildings and that it should be considered in design. Early studies on irregularity in elevation were devoted to discriminating which method of analysis was more appropriate to design irregular structures. More recently, many studies were devoted to judging the effectiveness of nonlinear static procedures in evaluating the seismic response of regular and irregular structures. Only few studies have focused on the detrimental impact that the irregularity in elevation may have on the structural response. In this paper, the seismic response of a wide set of RC frames with different heightwise distribution of stiffness is evaluated by pushover analysis. Hence, the seismic performance of the frames with irregularity in elevation is compared with that of the regular ones. The results have shown that, if capacity design criteria are used to size structural members, story collapse mechanism is never achieved and frames with irregular distribution of stiffness exhibit a suitable seismic performance even if designed by the reference (unreduced) behaviour factor.