An experimental and numerical insight into the unbonded and partially bonded high-damping fiber-reinforced elastomeric isolators

Elastomeric isolators are commonly used for seismic isolation. Typically, they are composed of alternating rubber pads and steel laminas. The composite action provides horizontal flexibility through the rubber and vertical and rotational stiffness through the steel. However, due to costs, they are mainly limited to use in strategic, nonresidential structures, especially in developing countries. A new elastomeric device, the fiber-reinforced elastomeric isolator (FREI), has been developed using fiber layers instead of steel laminas, reducing costs. FREIs offer bonded (traditional), unbonded, and partially bonded applications. In the unbonded setup, FREIs are placed between structures and foundations without any bonding or fastening. The shear load is transferred through the friction generated between the isolator and the structure surfaces, improving the seismic performances and the damping ability compared to the same device in a bonded condition. However, they can't resist vertical tension. The partially bonded approach addresses this by partially attaching the contact surfaces of the device to connection steel plates, retaining the advantages of both bonded and unbonded methods. Central to the efficacy of these isolators is the rubber material itself. Natural rubber (NR) is the most used, but artificial rubber is promising for the fabrication of isolators because NR has a poor damping performance, it is vulnerable to quick aging, and its industrial production is of concern. Factors such as escalating demand, price fluctuations, high labor costs, trade policies, and a ban on deforestation have made NR production unreliable. This paper presents an in-depth investigation of circular high-damping FREIs in both partially bonded and unbonded applications. The study employs a combined numerical and experimental approach. It provides a detailed explanation of the design process, numerical modeling, and experimental characterization for both the rubber material and the seismic devices, highlighting the advantages of design optimization based on preliminary numerical results. This methodology can serve as a valuable example, offering significant help to manufacturers and engineers. Additionally, a novel simplified analytical model is introduced for the employment of unbonded and partially bonded FREIs in structural applications, based on the fitting of cyclic shear tests used for the characterization of the dynamic properties of the elastomeric devices.