SEISMIC RETROFIT WITH HYSTERETIC BRACING OR FVD
In addition to seismic isolation, seismic retrofit with hysteretic bracing or fvd improvement/adjustment of existing buildings is often achieved through the use of dissipators, usually inserted into framed structures as components of dissipative bracings, that is, by using inter-storey displacement to dissipate energy.
Energy dissipators are divided into two families:
– Displacement dependent devices, typically based on the hysteretic properties of SOMMA HBF type metal elements
– Speed-dependent devices, that is cylinder/piston devices (either MC type hydraulic or fluid-dynamic) that exploit the viscous dissipation due to the passage of particular fluids through a suitable hydraulic circuit. The resulting constitutive bond depends on the speed, usually with a non-linear dependence that maximises the dissipative capacity.
The insertion of dissipators in a structure greatly reduces the need for ductility in the structural elements, and therefore greatly improves the ability of the structure to withstand an earthquake.
However, it is not always possible to keep the structure completely elastic, and thus wholly avoid damage to it.
However, a high level of safety can always be achieved, with excellent cost-benefit ratios. It should also be noted that, unlike seismic isolation which is not always feasible in an existing building, the insertion of energy dissipators into an existing framed building is almost always feasible, although architectural implications have thus far limited its use mostly to public buildings, especially schools.