Long-Period Isolation System Using Low-Modulus High-Damping Isolators for NuclearFacilities at Soft-Soil Sites

摘要

An experimental study was undertaken to consider the performance of isolatedstructures under levels of earthquake attack beyond the design level, and in the case of facilities located at soft-soil sites of the effect of a low-site natural frequency on isolated structures. The safety requirements for nuclear facilities are such that the behavior of the system for beyond design level events must be addressed. A scale-model structure was built and two sets of model isolators were developed for the structure to give prototypic structure frequencies of 0.4 and 0.3 Hz, respectively. Shake table tests were carried out to assess the safety of the base isolation design for a nuclear facility under a number of realistic ground motions characteristic of the site. These ground motions included the effects of the site frequency, the degree of embedment of the structure and the anticipated soil-structure interaction of the isolated structure. The model represented, at a scale factor, the overall inertial properties of the structure but not local detail. Two different isolation systems were used in the tests: One was designed to provide the model with a natural period that corresponds to the period of the proposed nuclear facility. The other made useof a newly developed high-damping rubber with a low shear modulus which provides a frequency about 25% lower than that given by the first system. This allowed the assessment of (1) the benefits of lengthening the period of the isolation system where the site is particularly soft and (2) the practicality of long-period isolation systems based on elastomeric components.