Discrete rotating links model for the non-linear torsion-shear behaviour of masonry joints

The numerical modelling of the torsion behaviour of masonry block interfaces is a key aspect for the assessment of the out-of-plane response of masonry walls. Nevertheless, it still represents a challenging computational issue due to the high non-linear coupling between the torsion and other internal forces (shear, bending moment and axial load), which rigorously requires the adoption of complex three-dimensional non-linear constitutive laws. This paper originally introduces a simplified discrete inelastic interface able to simulate the non-linear torsion-shear behaviour of masonry contact joints, within the context of static incremental analysis. The more general mechanical behaviour of the interface is ruled by six degrees of freedom and is governed by four rotating links, whose actual orientation is updated during the step-by-step analysis, by taking into account the current position of the twisting centre of the interface. The incremental torsion-shear capacity curve and the corresponding ultimate domains obtained by the proposed model are compared with the ultimate load limit analysis predictions and with some experimental data available in the literature. The results highlight the ability of the new discrete interface to effectively reproduce the full non-linear behaviour of masonry contact interface subjected to different loading combinations.