Shake table testing of a seismic isolation system for lightweight structures

Abstract

The implementation of seismic isolation in lightweight structures, such as houses, is limited, except for Japan, where nearly 5000 houses are seismically isolated with highly engineered systems. The use of such systems in countries of growing economies is prohibitive due to their cost, difficulties in locally fabricating components, and incompatibility with local construction practices. Previous studies on low-cost isolation systems showed that isolation devices with rolling rather than sliding elements are more suitable for lightweight structures. A low-cost isolation system based on a deformable rolling bearing developed at the University at Buffalo has simple components that can be easily manufactured, has a large displacement capacity, and features a fail-safe mechanism. The bearing is composed of one flat and one concave concrete plate and a rubber rolling ball. This paper presents the results of shake table testing of half-length scale versions of prototype houses and small bridges equipped with this deformable rolling isolation system in three-directional seismic excitation. The results showed that deformable rolling bearings provide significant seismic protection of lightweight structures against strong ground motions, which in the testing reached a maximum peak ground velocity of 1.2 m/s in the test scale and a peak ground acceleration of 4 g in the horizontal direction and up to 1 g in the vertical direction. The isolation system was particularly effective in the horizontal direction, whereas it did not provide any vertical isolation. The tests included cases of extreme response, which included vertical impact within the bearing's components and uplift of the isolated structure.