Seismic isolator and method for strengthening structures against damage

Abstract

A seismic shock isolator and method of strengthening structures against seismic shock. The shock isolator includes a cylinder having a damping chamber and an accumulator chamber and a piston movable into the damping chamber. The damping chamber can contain compressible liquid or incompressible liquid. The piston has a damping head and a first control orifice, and the accumulator chamber is separated from the damping chamber by a wall having a second control orifice having a higher exponent than the first control orifice. Movement of the piston into the damping chamber creates a combination of damping and stiffening having a spring component. When the isolator has compressible liquid therein, the spring and stiffening is produced by a compression of the liquid. When the isolator contains an incompressible liquid, the stiffening and spring component are obtained by a yielding of a column which movably supports the wall which divides the damping chamber from the accumulator chamber. The method protects the structure against damage due to seismic forces having a band of frequencies, and it includes the placement of a passive restraining seismic isolator of the above type in the structure and applying a combination of hydraulic damping and frequency dependent stiffening with a spring component to the structure in response to the structure being subjected to seismic forces.