Research on the influence of offset separation on the seismic performance of unanchored and semi-anchored laminated rubber bearings

Laminated rubber bearings, known for their simple construction and ease of installation, are extensively utilized in small and medium-span bridges. However, recent studies have revealed that these bearings are vulnerable to various types of diseases during their service life, with offset separation being the most prominent. This condition subjects bearings to abnormal compression, reducing their load capacity and deformation ability. In response to this issue, experimental investigations were carried out to assess the mechanical performance of unanchored and semi-anchored bearings under different initial separation conditions. A series of 12 operational scenarios were examined using unidirectional shear and hysteresis shear tests. The results show that the equivalent shear stiffness of the bearings decreases with the increase of the initial separation area. The equivalent damping ratio shows minimal change at low shear strains but increases significantly at high shear strains due to slippage and failure of the bearings. Comparing different bearing anchoring methods reveals that the friction coefficient of semi-anchored bearings is slightly lower than that of unanchored bearings. However, the friction coefficients for both anchoring methods generally fall within the range of 0.15 to 0.25. Furthermore, the mechanical degradation of semi-anchored bearings occurs earlier, leading to premature failure compared to their unanchored counterparts.