Base isolation for increased earthquake resistance of buildings

Abstract

Inelastic deformation and hysteretic damping increase the earthquake resistance of structures beyond that provided by their elastic strength. For many structures the reserve flexibility and the damping could be supplied efficiently and reliably, by the use of special components.

Special components are most effective when they are located at the interface between the lowest part of the building and the foundations. Recently developed hysteretic dampers, utilizing the plastic deformation of solid steel bars, may be combined with one of the many methods suggested for achieving base flexibility to give a practical and efficient base-isolation system.

In addition to reducing the general level of attack a base-isolation system greatly reduces the variation in severity of
 attack resulting from differences in character between earthquakes. In view of the range of earthquake types to which a structure may be subjected this "standardization" of the earthquake attack is important, and is found to be particularly important for structures with a fundamental period of less than 0.4 seconds.

A base-isolation system reduces ductility demands on a building, and minimizes its deformations. These changes improve building performance and allow much greater architectural freedom in the choice of the structural type and in its layout and detailing. Economies are increased and performance improved by using high-strength low-ductility structural configurations.