Stability of elastomeric bearings for seismic applications
Sanchez Ferreira, Jose A.
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Elastomeric seismic isolation bearings have been shown to effectively mitigate structural and nonstructural damage during earthquakes. During strong shaking, elastomeric bearings need to carry high axial loads while being subjected to large lateral deformations. An appropriate evaluation of the critical load for moderate as well as for large displacement (shear strain above 100%) is essential to avoid an undesirable failure of the isolation device at high axial loads. This study presents results from an on-going experimental program to examine the performance limit states in seismically isolated buildings. The specific objective is to compare two different experimental procedures to evaluate the critical load of an elastomeric bearing and compare them to analytical prediction. The first procedure to evaluate the bearing critical load followed a previously used experimental method were the elastomeric bearing is held to a specified horizontal displacement while applying increasing axial load until the critical load is achieved. The second procedure proposed here first applies a constant axial load followed by a lateral displacement until reaching the stability limit of the bearings. The second procedure proposed in this thesis showed to be an accurate and direct approach to obtain the critical load directly from the stability test data and considerably minimizes the data analysis required as in the first procedure. The reduced area formulation commonly used to predict the critical load of the elastomeric bearings is compared to the experimental results. Here, it is recommended to use the effective shear modulus at small shear strains in order to get better agreement with experimental results. In addition, the shear strain and pressure distribution is computed analytically to examine the state of the bearing material at the instability point.