Numerical model for the response of unbonded FREI at low temperatures

Fiber-reinforced elastomeric isolators (FREI) are a relatively recent development in base isolation research. Consisting of layers of elastomer and fiber cloth, FREI can be cut to size from a larger sheet into any desired size or shape. Compared to traditional isolators reinforced with steel shims, FREI can potentially provide cost savings and allow for a large reduction in weight. FREI have been tested extensively to evaluate their behavior under lateral, vertical and rotational deformation, including combinations of the three deformations simultaneously. Results from these studies have shown FREI to be a viable option for use in both buildings and bridges. Throughout North America, bridges are built in a wide array of climates, with temperatures in some regions reaching extreme lows. Isolators installed in these bridges must be able to perform adequately at low temperatures. A recent experimental study was completed on unbonded FREI (U-FREI) subjected to low temperature conditioning. Specimens were held at temperatures as low as -37°C for as long as 28 days. Results from this research indicate adequate performance at low temperatures was achieved. Using these results, an existing numerical model for the behavior of U-FREI has been modified to account for the effect of low temperature conditioning. This updated model will be used in a future study to simulate a bridge located in a cold, northern climate that is isolated with unbonded FREI.