Numerical study on the response of steel-laminated elastomeric bearings subjected to variable axial loads and development of local tensile stresses

Steel-laminated elastomeric bearings are isolation devices which are used extensively in buildings, bridges, nuclear power plants and other structures. Accurate modelling of the behaviour of these devices is of great importance, as the integrity of isolated structures relies heavily on their response. For many years, steel-laminated bearings were designed based on the assumption that they are subjected to compressive and shear loads, as a result of the dead and the horizontal loads, i.e. wind and seismic loads, acting on the structure. It is only very recently that tensile stresses in bearings were studied, as it was observed that local and global tensile stresses might be developed in bearings under seismic excitations. Most importantly, tension within the elastomer might cause local cracks or, in extreme cases, rupture of the elastomer, which might lead to the loss of support of isolated structures. Yet only a few studies exist in the international literature with regard to response of these devices under combined axial and shear loads. The aforementioned gap in the knowledge and the identified rupture of the elastomer of bearings under tensile loads during recent earthquakes comprised the motivation for this research. In this context, this paper examines the response of steel-laminated elastomeric bearings under cyclic shear and variable axial loads and aims to better understand their behaviour with emphasis placed on the tensile stresses within the elastomer, their stiffness and dissipation capacity. Extensive numerical research was conducted with ABAQUS and the Ogden hyperelastic model was used for modelling the elastomeric material. The analyses showed that steel-laminated elastomeric bearings exhibit local tensile stresses, which alter significantly their stiffness and damping ratio. Most importantly, significant tensile stresses within the elastomer were observed locally, even when the bearings were subjected to a combination of shearing and compression.