A seismic insulator based on wire rope spring and BTU

Seismic insulators must have low horizontal stiffness values so that the fundamental period of the suspended mass is well above the predominant period of the earthquake and high vertical stiffness values to limit the vertical deflection caused by the weight of the suspended mass. Wire rope springs do not have this feature but they can operate as seismic insulators if used in parallel with a device that is capable of bearing the supported equipment weight and allows it to move in any horizontal direction with low friction. With this aim, the results of tests conducted on a seismic insulator prototype comprising a wire rope spring and a ball transfer unit (BTU) are reported in this paper.