The role of capacity and flexibility of floor diaphragms in the seismic retrofit of existing RC buildings

The renovation of existing buildings to improve the safety and resilience of our building stock is now recognized as a priority, and many retrofit techniques have been recently proposed, especially carried out from the outside to avoid inhabitants’ relocation. The ability of the existing floors to act as seismic diaphragms is however rarely addressed, if not in terms of diaphragm flexibility. Analyzing data from numerical and experimental studies carried out on a real beam and block floor system, some considerations about the role of existing diaphragms on the structural response of RC buildings are made with particular emphasis on in-plane capacity, deformability, and collapse mechanisms. Practical implications for the design of seismic retrofit interventions are defined.