The concrete strength variability as source of irregularity for rc existing buildings

Existing buildings can easily present material mechanical properties which can largely vary even within a single structure. As a consequence of the high strength variability, at the occurrence of seismic events the structure may ev-idence unexpected phenomena, like torsional effects, with larger experienced de-formations and, in turn, with reduced seismic performance. This work is focused on the reduction in seismic performance due to the concrete strength variability. The analysis has been performed on a case-study, i.e. a 3D RC framed 4 storey building. A normal distribution, compatible to a large database, has been taken to represent the concrete strength domain. Due to the introduced strength variability, a stiffness and strength eccentricity arises at the first storey of the structure, with a consequent increase in its seismic response. The capacity (C) of each column of the case study, found according to EC8 prescriptions, has been compared to the demand (D), for three different limit states. The seismic performance found by ac-counting for the strength variability has been compared to the one provided by the EC8 standard procedure, which has resulted to be conservative in the seismic re-sponse estimation and in the evaluation of the torsional effects, while it is not con-servative in quantifying the seismic performance of the case-study.