Finite element analysis of laminated rubber bearings under compression and shear

Abstract

Laminated rubber bearing is an accepted and trusted structural element for accommodating various movements in bridges. Base isolation of structural systems and sensitive components also employ similar devices. This approach has considerable potential in protecting the structures and their equipments from vibrations by extending the natural period of the structures and thereby reducing the stresses involved. The bearing pads get primarily compressed on vertical load but also need to accommodate lateral shear movement and rotation about horizontal axis. For predicting the behavior of laminated rubber bearings, three dimensional finite element analysis is performed in this study at small and finite strain domain. The analysis fully takes rate independent monotonic material nonlinearities as well as geometrical nonlinearities into account. To achieve this, an improved hyperelasticity model of rubberlike materials proposed in Amin et al. (2006a,b) is implemented in a general purpose finite element program. Analytical derivations of stress and elasticity tensors are coded for finite element implementation. The material parameters necessary for simulation are used from previous experimental observations (Amin et al. 2006a). Using the constitutive model and the finite-element method, three-dimensional finite element simulations of natural and high damping rubber has been conducted in compression and shear regimes. For verification purpose, similar geometry and boundary conditions of the experiments were maintained in numerical models. The simulation results are found to be in good agreement with the available experimental results in compression and shear. Thus the adequacy of the developed finite element procedure in simulating nearly incompressible material response under uniaxial compression and simple shear is verified. Three-dimensional finite element models of single, double and multilayer rubber bearings are constructed for performing simulations in compression and shear regimes. Simulation results for single layer rubber bearings of different shape factors showed significant differences with analytical results. The FEM solutions were found to be more realistic than analytical results. For multilayer bearings, the effect of shape factor, bulk modulus and mesh size are found to be significant and logical to govern the compression behavior. Furthermore, bridge bearings with shorter steel plates and softer grades of rubber at the edges were found to give reduced stresses under non uniform compression producing rotational effects. The new hyperelasticity model was found to give lower bound results than conventional Mooney –Rivlin model in these cases. Finally, a parametric study for such bearings with different shape factors has shown that larger stresses are developed at bearings with higher shape factors or harder grades of rubber.