A simple seismic isolation system by leveraging buoyancy has been devised for spread foundation structures. Through dynamic centrifuge tests, it is shown experimentally that a sliding isolation effect arises during seismic loading if a buoyant force of appropriate magnitude is applied to the base of the foundation. It is confirmed that seismic isolation performance tends to improve as the buoyancy-to-weight ratio increases. Performance when the buoyancy-to-weight ratio is 90% or more is particularly good, and the maximum response acceleration of a structure can be reduced to below 100 cm/s2 against a sinusoidal wave with a maximum acceleration of 500 cm/s2.
