In this work, the base isolation system for a multi-storey reinforced concrete building, highly irregular in plan, has been considered. The hybrid base isolation system consists in High Damping Rubber Bearings (HDRB) in parallel with Friction Sliders (FS) with low coefficient of friction at the interface steel-PTFE. In particular the HDN.E 500 and AlgaPot PNm devices are adopted. The seismic analysis has been performed with all possible linear and nonlinear dynamic analysis according to Eu- ropean seismic code (EC8) and according to the new Italian seismic code (NTC 2008). The results of the seismic analysis have been compared closely, in terms of stresses on the main elements of the superstructure (bending mo- ment and shear force for the beams; biaxial bending moment, the axial and shear force for columns) and in terms of deformation of the superstructure (interstorey drift). In this work, has been evaluated the influence of the accidental eccentricity in the non linear dynamic analysis in order to account for uncertainties in the location of masses and in the spatial variation of the seismic motion. Con- sidering the accidental eccentricity in a nonlinear dynamic analysis, the number of tests to be performed increases substantially, so it is important to understand how the accidental eccentricity influences the seismic response of base-isolated structure.
