Supplemental damping techniques are increasingly applied in the field of seismic retrofit of frame buildings. Among these techniques, “mainly dissipative” (MD) ones, i.e. capable of supplying a high damping action without significant stiffening effects of the structural system, are preferred when rather stiff structures are dealt with in current conditions. A typical example in this field, represented by a MD-based retrofit intervention designed for a school gym in Florence, built in 1971, is presented in this paper. The structure is regular, but with dynamic properties significantly different along the two main directions in plan. A careful reconstruction of the characteristics of the constituting members, based on the original design documentation and on-site testing campaigns, helped analyzing in detail the seismic response of the structure in current state, highlighting the most critical elements. The MD-type system adopted as retrofit solution consists in a set of dissipative braces incorporating fluid viscous dampers, sized by an energy-based design procedure recently proposed by the first author. A performance analysis carried out in retrofitted conditions assesses that the targeted performance assumed for the intervention, consisting in an elastic structural response up to the maximum considered earthquake, is reached, along with an optimal level of the damping capacity of the dissipaters.
