The Earthquake Engineering Online Archive

A long-period isolation system using low-modulus high-damping isolators for nuclear facilities at soft-soil sites

Kelly, James M.

UCB/EERC-91/03, Earthquake Engineering Research Center, University of California, Berkeley, 1991-03, 194 pages (625/K44/1991)

An experimental study was carried out on a 6 m x 6 m shaking table using base isolation for a nuclear facility at the Savannah River site in South Carolina. This deep-soil site could have significant motion at the period range generally used for base-isolated structures. 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 Hz and 0.3 Hz, respectively. The objectives of the shaking table tests were to assess the safety of the base-isolation design for a nuclear facility under a number of realistic ground motions characteristic of the site, including frequency, degree of embedment of the structure, and anticipated soil-structure interaction. Two different isolation systems were used. One was designed to provide the model with a natural period that corresponds to the period of the proposed nuclear facility. The second system made use of a newly developed high-damping rubber with a low shear modulus which provides a frequency about 25 percent lower than that given by the first system. A set of earthquake records was developed using the known properties of the site and including potential soil-structure interaction, and the isolated model was tested on the shaking table. Then, a set of full-size isolators was made using the new soft compound and installed in a base-isolation demonstration building in Japan. An extra isolator was made and tested to verify the mechanical properties and ultimate capacity of the system.

Available online: http://nisee.berkeley.edu/documents/EERC/EERC-91-03.pdf (6 MB)