*2.1.3. Elastomeric isolators (non-dissipating)*

This kind of isolators consists in a rubber bearing made up of layers of elastomer.

These devices are characterised by low horizontal stiffness, high vertical stiffness and negli‐ gible damping capacity. These characteristics permit to increase the fundamental period of vibration of the structure and to resist to vertical loads without appreciable settling.

The fundamental design parameters used to determine vertical and horizontal stiffness are the geometrical characteristics (overall dimensions and thickness) and the mechanical character‐ istics of the elastomeric compound that is characterised by an effective dynamic shear modulus *G* equal to 1.4 MPa.


**Chart 3.** Features of the sliding isolators used in the analysis. *K*r is the restoring stiffness, *K*e is the equivalent stiffness (in case of linear analysis), ξe is the effective viscous damping, *F*0 is the friction force developed by the isolator and *F*max is the maximum horizontal force.

The compounds contain suitable antiageing additives that guarantee limited variation of the physical and mechanical characteristics in time.

Their behaviour is modelled as linear by means of the equivalent stiffness. Five types of isolators have been defined. All the parameters, characterising the devices, are specified in **Chart 3** since the vertical load on each support is different, being a continuous deck.
