Stability of fiber-reinforced elastomeric bearings in an unbonded application

Stable unbonded fiber-reinforced elastomeric isolators (SU-FREIs) are a viable device for seismic mitigation purposes in low-rise structures. SU-FREI bearings consist of alternating layers of elastomer and fiber fabric with shape factor and aspect ratio such that stable rollover occurs during lateral displacement. This study investigates the stability of SU-FREI bearings through experimental testing. Two experimental test procedures are employed. The first investigates stability during incrementally increasing axial loads under lateral cyclic excitation, and the second investigates the ultimate shear properties of SU-FREI bearings through monotonic lateral displacement under design axial load. Dynamic stability testing reveals that the tested SU-FREIs remain stable at axial loads significantly greater than the design load under a wide range of cyclic lateral displacement amplitudes. In addition, an increase in axial load results in lower effective stiffness and greater effective damping in the SU-FREI bearings. Although rollout instability was not encountered during ultimate shear property testing, shear tests provide insight into the stiffening effect encountered as the originally vertical faces of the SU-FREI bearings make contact with the top and bottom contact supports.