Base isolation represents one of the most effective solution for passive protection of structural systems against earthquakes. The main principle of such a technique is related to the reduction of internal forces and deformation of a given structure, by means of an isolation level, able to dissipate significant amounts of energy and to accommodate large displacement demands. This behavior can be achieved if isolation devices are properly designed. Several isolation technologies have been deeply investigated, such as Rubber Bearings, Lead Rubber Bearings and both Single and Double Concave Surface Sliders. In addition, Multi-Stage Concave Surface Slider devices have been also studied, especially for high seismicity regions. Such devices provide different responses, depending on the achieved displacement demand: high tangent stiffness is provided for both low and high intensity levels, whereas low tangent stiffness is designed for medium seismic excitations. In this work the seismic response of Multi-Stage Concave Surface Slider devices has been analyzed, by considering the available non-linear models found in the scientific literature, according to the experimental behavior. Special attention has been focused on the frictional properties, the definition of the tangent stiffness of each stage and the main modeling scheme of the device
