On the torsional effects in RC framed building due to the strength variability of concrete

A proper assumption for the concrete strength is essential to model RC existing structures. In this paper the variability of concrete strength within the buildings is investigated as a source of plan irregularity. The study has been made on a case-study, i.e. a 4-storey RC framed building. The variability of the concrete strength has been evaluated on the base of an extensive experimental investigation. A coefficient of variation of 30%, consistent with the available database, has been assumed in the analysis. As regards the role of the strength variability on the seismic demand, the increase in the seismic response due to the torsional effects is covered by the mass eccentricity equal to 5% suggested by Eurocode 8. As regards the effects of the strength variability on the structural capacity, instead, the current approach of Eurocode 8 does not result to be conservative when compared with the most unfavourable cases of the analysis.