Advanced shear and axial laws of bearings in the nonlinear seismic analysis of r.c. buildings

Base-isolated reinforced concrete (r.c.) framed structures may be subjected to amplification of seismic demand in the superstructure and complex shear-axial interaction in the isolation system at sites located near an active fault. Advanced mathematical models to predict the highly nonlinear behaviour of elastomeric bearings (e.g. high-damping-laminated-rubber bearings, HDLRBs), when subjected to a combination of severe horizontal displacement and significant variation of the axial load, have been recently proposed in the literature and verified with experimental data. The aim of the present work is to evaluate the effects of these advanced formulations in shear, axial and rotational behaviour of HDLRBs on the nonlinear seismic analysis of r.c. base-isolated structures. New and retrofitted base-isolated five-storey r.c. framed buildings are designed in a high-risk seismic zone. Simplified and advanced load-deformation laws are compared on the basis of a three-degree-of-freedom model of the HDLRBs including horizontal and vertical displacements and rotation. Nonlinear incremental dynamic analysis of the test structures is carried out considering near-fault earthquakes recorded at different stations. Results show that property modification factors should be introduced in bounding analysis procedures to include the effects of advanced nonlinear modelling of the isolation system.