ABSTRACT
There are two ways of protecting structures from the effects of earthquake ground motions. The first one is based on the conventional design philosophy, and the second – on the structural response-control. Two aspects of earthquake engineering are considered in every structural design project for a retrofit of an existing building: demand and capacity. Usually we take the demand as a given, and attempt to incorporate into the building the capacity to resist the demand. An alternative approach is to reduce the demand on the structural system by using seismic isolation (or base isolation). The fundamental mode of the isolated structure involves deformation only in the isolation system, the structure above being almost rigid. This makes isolation a very attractive approach for seismic retrofitting of existing structures. The method is especially suitable for seismic protection of historical buildings, part of the cultural heritage of a country.
