Glazed-level dissipative brace incorporation in a gym building

A wide stock of reinforced concrete (RC) gyms and sports halls has been built from 1960s through 1990s in Italy with similar architectural characteristics, including a two-level partition of façades, with continuous masonry infills placed in contact with the frame structure on the lower level, and ribbon windows on the upper glazed one. A school gym built in 1976, well representative of this stock of edifices, is examined herein. The assessment study in current state is carried out via non-linear dynamic analysis, modelling the infills by means of equivalent diagonal struts, and the RC members by plastic hinges. The response of the ribbon windows, not expressly simulated in the analysis, is checked in terms of relevant inter-level drift. The results show a significant inelastic response of the infill panels and the RC columns, and very high drifts of the glazed level, corresponding to full collapse conditions of the ribbon windows, for the Basic Design Earthquake (BDE)-scaled seismic action. Consequently, a retrofit hypothesis is proposed, based on the installation of a dissipative bracing system incorporating pressurized fluid-viscous devices on the glazed level, and conventional braces on the infilled level. The location of the system implies no architectural intrusion in the interiors and interruption in the usage of the building. The analyses in post-intervention conditions highlight a remarkable response reduction in terms both of drifts and stress states, consistently with the target design objectives. This allows reaching a safe response of structural elements and ribbon windows, and an elastic response of infills, up to the BDE.