Una tecnologia integrata isolamento - scorrimento alla base per il controllo del taglio sismico degli edifici

The seismic upgrading of existing r.c. buildings has become a pressing need, especially in the Mediterranean area. Indeed, the majority of the building stock is not able to sustain seismic actions, because it was conceived and designed to sustain gravity loads only, or for seismic actions lower than those expected from the current seismic zonation. A large variety of retrofit techniques has been developed and proposed during the last decades, among which the base isolation is deemed as one of the most effective. In fact, it is able to reduce the seismic force acting on the structure. Unfortunately, the seismic demand of the structure keeps increasing with the input magnitude. More recently, another possible retrofit intervention has been proposed by detaching the structure from the foundation to let the structure slide in case the seismic force overcomes the friction force. This intervention is able to cap the base shear of the superstructure to a value that is independent of the input magnitude. The main drawback is that the maximum value of the base shear can be significantly larger than the friction force and may overcome the structural resistance. Based on this background, this paper aims to explore the possibility of a new retrofit technique, named “isoslider”. This technique integrates the conventional base isolation technology with the sliding system. The goal is to compensate the deficiencies of the two technologies by exploiting their positive features. Indeed, on one hand the slider should cap the shear force in the structure to a value independent of the input magnitude, on the other hand the base isolation should reduce the amplification of the shear capping with respect to the friction force.” In this paper a design procedure of the isosliding system is proposed and the seismic behaviour of the isosliding system is investigated and compared to that of a fixed base structure, a base isolated structure and a sliding structure. To this end, a simplified two degree of freedom model was analysed by means of incremental nonlinear dynamic analysis.