Hysteresis Properties of Lead Rubber Bearings Under Horizontal Bi-Directional Deformation

Abstract

Reduction of the horizontal deformation capacity of elastomeric isolation bearings under bi-directional loading has been one of the major concerns since that such a phenomenon was observed for high-damping rubber bearings. Using a newly constructed loading machine, a series of tests of lead rubber bearings (LRBs) were conducted to investigate their detailed mechanical characteristics under horizontal bi-directional deformation in the paper. The influences of the configurations, such as shape of cross section, diameter of a lead plug and aspect ratio, on the bi-directional behavior were carefully examined. Simulation analyses were also conducted to predict the bi-directional behavior of LRBs.

Mechanical behavior of lead rubber bearings under and after nonproportional plane loading

“…As the test setup shown in Figure , it is noted that the upper and lower flange plates of the tested bearings were not twisted during the tests. Taking clockwise positive, the torsional (or twisting) moment at time t exerted on the flange plates because of nonproportional plane loading M t ( t ), as shown in Figure , can be calculated by where F x ( t ) and F y ( t ) are the shear force components at time t measured in X and Y directions, respectively.…”

“…In consideration of the dynamic capacities of the test setup, four different levels of vertical compression stresses and shear strains, together with three different levels of loading rates (excitation frequencies), are applied in the unilateral triangular (sinusoidal) reversal loading tests. The nonproportional plane loading tests include circular, figure‐eight, and square loading paths, which have also been adopted in some past experimental researches . For each plane loading path, two different levels of vertical compression stresses and four different levels of shear strains with a fixed excitation frequency are applied.…”

“…In a research by Nakamura et al elliptical and circular plane loading patterns were applied to experimentally study the hysteretic behavior and mechanical properties of LR bearings designed with circular and square sections as well as a single and quadruple lead plugs. Similarly, the bilateral coupling effect was observed, which will induce torsional deformation and increased local shear strain at the rubber, at the circumference in particular.…”

Practical application of lead rubber bearings with fail‐safe mechanism

“…This is due to the inconsistency of the directions of the restoring force and the damping force . The torsion of LRB is relatively small compared to that of HDR and both sectional shapes of the bearing (circular or square) and the number of lead plugs do not significantly influence the amount of torsional deformation of LRB . In contrast, the rubber part of general elastomeric slider bearings have different vertical distribution in the torsional strain compared to rubber bearings due to the asymmetric degree of fixation at the upper and lower ends .…”

“…The effect of torsional behavior on the maximum shear strain of the LRB component in bi‐directional loading shall be quantitatively evaluated because the fundamental concept of FSLRB is to initiate sliding before the LRB component exhibits an excessive shear strain. Moreover, the significance of both bi‐directional dynamic loading and the utilization of actual‐size specimens in isolation device testing is widely known as a result of progress in experimental studies . Considering the aforementioned facts, the authors conducted a variety of tests, including bi‐directional dynamic loading tests of actual‐size FSLRB specimens.…”