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In‐plane–out‐of‐plane non‐linear model of masonry infills in the seismic analysis of r.c.‐framed buildings

The out‐of‐plane (OOP) behaviour of masonry infills (MIs), inserted in reinforced concrete (r.c.)–framed buildings, is recognized as one of the most important failure modes of this nonstructural element during an earthquake, which may be a consequence of simultaneous or prior in‐plane (IP) damage. A five‐element macro‐model, with four diagonal OOP non‐linear beams and one horizontal IP non‐linear truss, with an equivalent mass of the infill panel divided between two central nodes, takes into account the IP and OOP failure modes occurring in the event of seismic loading. Pivot hysteretic models predict the non‐linear IP and OOP force‐displacement laws of the infill panel, based on geometrical rules defining loading and unloading branches. Firstly, a calibration of the proposed IP‐OOP interaction model of MIs is carried out considering full‐scale experimental results of traditional masonry typologies. Each specimen is initially subjected to in‐plane quasi‐static cyclic loading, until a maximum drift is reached, and then one‐sided OOP cycles are imposed pushing in the horizontal direction and back to zero force. Then a numerical investigation considers masonry infills of an existing six‐storey r.c.‐framed building designed in compliance with a former Italian seismic code. To evaluate the interaction, the results of simultaneous IP and OOP cyclic tests on MIs at the top, intermediate, and lowest levels of the test structure are presented, assuming different displacement histories: (1) OOP loading faster than IP, at the sixth storey; (2) equal IP and OOP loading, at the third storey; (3) IP loading faster than OOP, at the first storey. Finally, attention is focused on the contribution of masonry infills to the IP and OOP energy dissipation of r.c.‐framed structures.