Low-impact seismic retrofit technologies for school buildings

Supplemental damping strategies are increasingly adopted for seismic retrofit of frame structures also in consideration of their low-impact architectural and environmental characteristics. A further spreading of these technologies in the professional community strongly depends on the availability of simple design procedures, especially concerning the preliminary sizing of the dissipaters. A viable design criterion was recently proposed by the author to this aim and applied to the retrofit study of a reinforced concrete gym buiding. A new case study, namely a school building in Florence dating back to the early 1980s, is examined in this paper, so as to evaluate the feasibility of the criterion for a more complex structure. The building is composed of two portions, with reinforced concrete and steel frame structure, respectively. Similarly to several other buildings of the same period, the structure is infilled by heavy reinforced concrete panels interacting with the frame elements under horizontal loads. A careful reconstruction of the structural characteristics of the constituting members, based on the original design documentation and on-site testing campaigns, highlighted specific drawbacks in current state, related to a remarkable degradation of the materials and a poor performance of several elements. The retrofit solution considered in this study consists in removing the infill panels and replacing them with a set of dissipative braces incorporating fluid viscous dampers as protective devices. The design is carried out by the sizing criterion mentioned above, targeting an elastic structural response up to the maximum considered earthquake normative level. A performance analysis carried out in retrofitted conditions confirms that the proposed sizing criterion helps optimizing the mechanical characteristics of the dampers by carrying out simple procedural design steps.