Seismically Isolating a Structure: A Rational Approach for Feasibility Assessment and Definition of Basic Parameters

Although conceptually simple, the application of seismic isolation can pose dangerous pitfalls. It is based on decoupling the dynamic response of a structure from the ground motion by inserting isolation devices at its base. Significant displacements of the devices are typically required in return for increasing the oscillation period and reducing seismic accelerations in the building. To avoid blind guessing, the suitable values for damping and the period of vibration should be defined. The vibration period can vary in a range that depends on the capacity of the superstructure, which influences the maximum allowable acceleration, and the boundary conditions, which limit the maximum allowable displacement. In this regard, a simple and effective procedure is proposed for assessing the feasibility of seismic isolation and providing a preliminary yet reliable evaluation of the basic parameters, such as damping and the isolation period. This procedure could also highlight the need for changing the seismic protection strategy. Some application examples, aimed at including a wide range of design cases, are also provided.