Uni-axial shaking table tests and validations of a seismic isolation system made of spring tube braces

A new seismic isolation system based on spring tube braces was studied. An isolation story, which consisted of pin ended steel columns and spring tube braces, is arranged at the foundation level and/or any intermediate storey of the building. A series of experimental and analytical studies were carried out to evaluate the capability of the proposed seismic isolation system. Three storey ¼ scale 3D steel frames, with the proposed seismic isolation storey, were tested on the shake table using the real earthquake records. The transmitted accelerations from ground to floor levels were largely diminished by means of the isolation system, contrary to the fixed based specimen. Results showed no stability or self-centring problems for the proposed isolation system. The energy balance equations and dynamic force-displacement relations indicated that the equivalent damping arising from the seismic isolation storey was roughly 20%. This relatively high damping property, which can be attributed to the friction on the pinned connections of beam to columns as well as the period elongation, is effective for diminishing seismic response.