Seismic fragility of multistorey R/C frames with vertical irregularities

Structural regularity represents one of the most important principles governing the conceptual design of seismic structures, but it is also one of the most common structural deficiency observed in both existing and new buildings. Experiences of past earthquakes have shown that buildings with irregular configurations or asymmetrical distributions of structural properties trigger an increase in seismic demand, causing greater damage due to the concentrated deformations induced by structural discontinuities. The aim of this research is focused on the seismic behaviour of multistorey R/C plane frames with in-height irregularities. Regular models are developed and the irregularity has been introduced by degrading and upgrading the ‘stiffness-storey’ and considering different distributions of soft or stiff stories along the height of the structures. The seismic performance of irregular plane frames has been studied by means of Incremental Dynamic Analysis (IDA), the analysis have been performed in Opensees. The study allowed a critical evaluation of the effect of vertical irregularities in terms of seismic response.