As a result, the design approach with seismic isolation has the following advantages over fixed base buildings:
– Reduction of stresses on both superstructure and substructure;
– Elimination or strong reduction of damage, not only to the structure but also to the non-structural elements and to the content of the buildings;
– Drastic reduction of torsional effects also in irregular structures on the surface (since a correct arrangement of the devices is able to make the centre of mass coincide with the centre of rigidity);
– Greater architectural flexibility
It is easy to see how structural ductility requirements become secondary for buildings designed with seismic isolators at the base.
As a result, an isolated structure does not, in most cases, entail higher costs than traditional structures.
In particular, the following considerations apply:
– Design: the modelling of a building isolated at the base usually fits into the condition where the isolation system can be modelled as a linear equivalent, which does not involve greater design costs.
– We find two different types of benefits as regards the structural elements: reduction of the actions (and therefore of the resistant sections) due to the filtering action operated by the devices; savings in terms of materials and execution times (therefore of manpower) thanks to the simplification of the construction details under the regulations for isolated structures in seismic areas. By virtue of these advantages, the cost difference between a traditional structure and a seismically isolated one can be eliminated or even become beneficial for multi-storey buildings and/or in areas with a particularly severe seismic input.