Vol.20, No.3, 2020, pp. 303–312
UDC:

Unbonded fiber reinforced elastomeric isolator (U-FREI) is a device for improved seismic performance of low-rise buildings. Fiber layers are used as reinforcement to replace steel shims, as are normally used in conventional steel reinforced elastomeric isolator (SREI). Further, heavy steel-end-plates are not provided in U-FREI and this device is installed at the interface of foundation and superstructure without any connection. Shape factor (S), which is defined as the ratio of the loaded area to load-free area of an elastomer layer, is likely to have influence on the force-displacement behaviour of U-FREI. Most existing studies on U-FREIs are limited to low shape factors for scaled specimens (S < 10). In this study, effect of shape factor on the horizontal response of prototype U-FREIs (S > 10) under the vertical pressure and cyclic horizontal displacement simultaneously is investigated by both experiments and finite element (FE) analysis. It is observed that the effective horizontal stiffness of U-FREI with smaller shape factor is smaller than that of U-FREI with larger shape factor at any given amplitude of displacement. Further, peak values of compressive stress in elastomer layers of U-FREI with smaller shape factor are higher than those of U-FREI with larger shape factor, while peak values of shear strain in elastomer layers of these U-FREIs are quite comparable at any given applied displacement.

Keywords: base isolation, unbonded fiber reinforced elastomeric isolator, shape factor, rollover deformation, horizontal response