Concrete strength variability as a source of irregularity for existing RC 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 value suggested by Eurocode 8 can be not conservative, since it does not consider the increase in the demand due to a not homogeneous strength distribution and the reduced capacity of the weaker members. In this paper the concrete strength variability is investigated as a source of in-plan and in-elevation irregularity. The effects of the strength variability on the seismic response and performance are evaluated on a case study, that is a 4-storeys 3D framed building. The seismic response of the case study has been represented by performing a nonlinear static analysis, while the seismic performance has been measured in terms of chord rotation. Results obtained from the analysis have been compared with the Eurocode 8 previsions