Variability in concrete mechanical properties as a source of in-plan irregularity for existing RC framed structures

Mechanical properties of concrete can consistently affect the seismic performance of RC buildings. A proper determination of the concrete strength is therefore essential for a reliable modeling of the structure. The current European Technical Code, Eurocode 8, provides a criterion for the strength assumption related to the knowledge level of the structure, which does not take into account the variability of the strength. If the concrete strength is affected by a large variability, the conventional strength value suggested by Eurocode 8 can be not conservative, since it does not consider the possible torsional effects due to a not homogeneous strength distribution and the reduced capacity of the weaker members. In this paper the effects of the concrete strength variability on the seismic performance are investigated with a case study, that is a 4-storeys 3D framed building. The seismic response of the case study by assuming different amounts of strength variability has been compared with the Eurocode 8 previsions, both in terms of possible torsional effects and seismic performance.