The effect of common irregularities on the seismic performance of existing RC framed buildings

This paper deals with the seismic performance of irregular 3D RC existing framed structures subjected to seismic actions. More specifically the effect of the non coincidence between the mass and the stiffness centres on the seismic response of these structures is investigated. The analysis is performed on a 4 storey 3D framed sample structure designed for vertical loads only. A very detailed nonlinear model of the structure is implemented under the computer code SeismoStruct. The seismic response of the structure is analyzed performing a nonlinear incremental dynamic analysis. The obtained response domain is compared with the limit values provided by FEMA 356 for the different limit states. The effect of the introduced irregularities on the seismic performance of the structure is not negligible despite the low value of the eccentricity. The performed analysis evidences that a particular attention has to be paid to the seismic behavior of RC buildings realized in the 60’s and the 70’s, before the adoption of seimic codes, since even light irregularities can consistently affect their seismic performance.