Effects of nonlinear modelling of the base-isolation system on the seismic analysis of r.c. buildings

Long-duration and high-amplitude horizontal velocity pulses are expected at sites located near an active fault; these are able to generate notable displacement at the level of the isolation system and pounding effects between closely spaced structural parts (e.g. in the case of an insufficient seismic gap between the elevator and building). A base-isolated commercial building, recently built in the Sicilian town of Augusta, designed in line with the former Italian seismic code, is considered as test structure. In particular, an r.c. framed structure with rectangular plan, composed of a basement and three storeys above ground level, is seismically isolated with a hybrid system including sixteen high-damping-rubber bearings (HDRBs) and twenty steel-PTFE low friction flat sliding bearings (LFSBs). An elevator shaft with steel framed structure crossing the isolation level is also placed in non symmetrical way along the longitudinal axis. A computer code for the nonlinear seismic analysis of base-isolated r.c. framed structures is improved by adding advanced nonlinear models of HDRBs and LFSBs. Finally, nonlinear dynamic analysis of the Augusta building is carried out with reference to near-fault earthquakes selected from the Pacific Earthquake Engineering Research center database and scaled in line with the design hypotheses adopted.