Dissipative Roof Diaphragm for the Seismic Retrofit of Listed Masonry Churches

In the seismic retrofit of the existing masonry buildings, dissipative and deformable roof diaphragms could offer an efficient solution in cases where both the adoption of steel ties or stiff diaphragms would be ineffective. An innovative deformable, dissipative and lightweight roof diaphragm for the seismic retrofit of masonry churches is proposed. Such a diaphragm prevents the overturning of the side walls whilst allowing the onset of a controlled rocking mechanism. The specific diaphragm elasto-plastic response caps the seismic actions transferred by the roof diaphragm to the seismic resistant walls, in contrast to a rigid and a stiffened diaphragm. This effect is meant to mitigate the overload of the head walls, thus preventing their collapse or the need for their strengthening, which could require interventions invasive of the historical structure. The feasibility of the proposed retrofit strategy is assessed through the experimental characterization of a prototype diaphragm sub-assembly and non-linear dynamic analyses of the global response of two retrofitted reference buildings.