seismic isolation for designers and structural engineers

The isolator increases the natural period of the overall structure and hence decreases its acceleration response to earthquake-generated vibrations. The first-mode period and damping of an isolated structure, and hence its seismic responses, are determined primarily by the characteristics of the isolation system and are virtually independent of the period and damping of the structure. The building on the left is conventionally protected against seismic attack and that on the right has been mounted on a seismic isolation system. In time, these isolated structures will also provide a steadily increasing body of information on the performance of seismically isolated systems during actual earthquakes. The differences between the first-mode and total distributions largely arise from the difference between the free-free first-mode shape which was used in the sweeping procedure and the actual first-mode shape with base stiffness Kb.

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