Influence of timber diaphragms and wall-to-diaphragm connections on the out-of-plane response of URM façade walls

Masonry structures represent a significant portion of the built heritage and are still widely found in historic buildings. Their seismic response is governed by complex interactions between vertical walls, horizontal diaphragms, and their connections. This study presents a nonlinear modelling approach for unreinforced masonry (URM) structures, based on the calibration of their main components – walls, timber diaphragms, and wall-to-diaphragm connections – using available experimental data. Given that the connections are identified as the primary source of nonlinearity, walls and diaphragms are modelled as independent components, linked only at floor levels through nonlinear axial and shear connectors. A simplified two-story URM building is analysed through nonlinear static procedures, considering different floor configurations – traditional timber floors and retrofitted systems such as plywood panels and concrete slab – and two representative connection types: steel angle brackets anchored to timber beams and chemical anchors installed at diaphragm level. The analyses highlight the influence of both diaphragm and connection stiffness on the out-of-plane response of the façade wall. In particular, the study allows for the identification of distinct overturning and flexural mechanisms affecting the façade, as a result of the nonlinear tensile response of the connections at floor levels. The outcomes provide valuable insight into the global and local behaviour of URM buildings and support the evaluation of strengthening strategies involving diaphragm–wall interaction.