Finite element analysis of base isolated buildings subjected to earthquakeloads

A finite element formulation modelling hyperelastic quasi-incompressible ru bber-like materials (elastomers) is developed which takes into account larg e displacements and large elastic strains as well as inelastic effects. The capacity of laminated rubber-like materials to support high loads in compr ession and large displacements in shear is the principal reason for their u se in devices for seismic base isolation of structures. The energy-dissipat ion capacity of these devices is increased by using high damping rubber, wh ich is an elastomer incorporating carbon black particles, or having lead-pl ug insertion. The Ogden strain energy function has been used as a basis for the material model implemented in a total Lagrangian formulation, the stra in being decomposed into its deviatory and volumetric parts and the pressur e variable being condensed at element level. Mooney-Rivlin and neo-Hooke st rain energy functions can also be used by simply changing the parameters of the model. The stress-strain hysteresis, which appears when these devices are subjected to dynamic or quasistatic cyclic loads, has been modelled by frequency dependent viscoelastic and plastic constitutive models. The beari ngs have been modelled by means of an equivalent single element capable of describing the composite behaviour of the actual isolation system. The prop osed model is validated using available experimental results and it is prov ed to be a powerful tool in dealing with different bearings. Finally, resul ts for a six-storey base isolated building subjected to the El Centro earth quake are given. Copyright (C) 1999 John Wiley & Sons, Ltd.