Investigations on inter-storey seismic isolation as a technique for adding upper storeys

The inter-storey seismic isolation technique is becoming increasingly attractive for the seis-mic risk mitigation of buildings, also as alternative strategy to base isolation. The reasons for applying this technique can be various and of different nature, such as: architectural con-cerns, feasibility of construction, and performance benefits. An interesting application of this technique concerns its use for adding upper storeys to existing buildings, avoiding the in-crease of seismic forces on the substructure, or even reducing them. Therefore, this technique could also be effective for seismic retrofit applications, using the mass of the superstructure as a nonconventional TMD for controlling the dynamic response of the substructure. Among the main issues concerning this application, there is the need to control the relative displacement between the two structural parts and the acceleration of the superstructure, while improving the seismic performance of the substructure. In this paper, a multi-objective optimization method for the dynamic characteristics of the ad-ditional superstructure is presented, which uses a TMD approach and considers the perfor-mances of the substructure, isolation system and superstructure. A 3-storey (3 DOF) case study structure was taken as a reference, analysing a wide range of isolated masses, isolation periods and damping ratios. Time-history analyses are finally performed, based on the opti-mization results, in order to assess the effectiveness of both the optimization method and the isolation technique, also considering the structural non-linearity.