Glazed-level dissipative brace incorporation in a gym building

A wide stock of reinforced concrete (RC) gyms and sports halls was built in Italy from 1960s through 1990s with similar architectural characteristics, among which the two-level partition of façades, displaying continuous masonry infills full in contact with the frame structure on the lower level, and glazed ribbon windows on the upper level. A school gym built in 1976, well representative of this stock of edifices, is examined herein with the aim of assessing its seismic performance in current state and proposing a supplemental damping-based retrofit solution capable of providing adequate protection both to the structure and the non-structural elements. The assessment study is carried out via non-linear dynamic analysis, by modelling infills by means of equivalent diagonal struts, and 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 on the glazed level, resulting in full collapse conditions of the ribbon windows, under a Basic Design Earthquake (BDE)-scaled seismic action. Consequently, a retrofit hypothesis is conceived, 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 or interruption in the usage of the building. The analyses in post-intervention conditions highlight a remarkable response reduction both in terms 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.