Seismic isolator

Seismic isolator apparatus placed between a foundation including a floor slab, and an objective to be protected from an earthquake to reduce a responsive acceleration arising therefrom, comprising:

• a combination of an upper friction plate and a lower friction plate which are in frictional contact along a friction plane;
• the upper friction plate being fixed to the objective;
• the upper friction plate being made from polyacetal resin containing lubricating oil;
• the lower friction plate being fixed to the foundation;
• the lower friction plate being made from a hard chromium-plated plate;
• the lower friction plate having a slide plate together with a damping rubber sheet, which is placed on the foundation;
• a height adjuster for supporting the objective and having a ball joint on said upper friction plate, the height adjuster being inserted between slide blocks to be vertically guided by the slide blocks and the slide blocks being fixed to a cover plate on which the objective is positioned;
• a horizontally positioned spring system fixed to the objective and to the foundation, said spring system comprising a spring, a wire element, a length adjuster and a pulley fixed to the foundation, the spring being hooked by means of the wire element over the pulley at a right angle and being fixed to beam elements of the objective at both ends, the length adjuster introducing a pre-tension into the spring system so that the spring system operates within a predetermined area of tension where the tension varies in response to a work load;
• and
• a damper having a wire element, a pulley fixed to the foundation, and a length adjuster which adjusts the length of the wire element, the wire element being hooked horizontally over the pulley at a right angle and fixed to beam elements of the objective at both ends.