Experimental determination of the lateral stability and shear failure limit states of bridge rubber bearings

This paper aims to increase the existing experimental knowledge base concerning the limit states of performance of natural rubber elements that are typically used as bearing pads and seismic isolators for bridges. A large experimental study is performed on 13 reduced-scale and 11 full-scale natural rubber specimens subjected to different types of shear-compression tests. Both lateral stability and shear failure under realistic axial compression forces are addressed in the study, together with an investigation of different isolator sizes, shape factors and slenderness ratios. Stability curves are obtained from tests using the constant displacement method, and shear failure data from tests using the direct method are presented. Predictions of the critical buckling loads from different versions of the reduced area method are compared to the experimental stability curves, indicating that these commonly used estimates are not always conservative depending on the geometry of the bearing. Several buckling and shear failure test results obtained in this study specifically highlight the fact that the slenderness ratio is the most critical parameter when determining the ultimate limit states of rubber bearings, although this parameter is often neglected. The intermediate limit states before buckling or shear failure are also investigated. It is shown that such limit states of performance are nearly impossible to define experimentally because most bearings do not exhibit any visual damage before failure, although experimental data indicate that slight to moderate damage obviously occurs in bearings under large displacements.