Distinct element modelling of the in-plane cyclic response of URM walls subjected to shear-compression

The in-plane capacity of unreinforced masonry (URM) elements may vary considerably depending on several factors, including boundary conditions, aspect ratio, vertical overburden, and masonry texture. Since the overall system resistance mainly relies on the in-plane lateral capacity of URM components when out-of-plane modes are adequately prevented, the structural assessment of URM structures could benefit from advanced numerical approaches able to account for these factors simultaneously. This paper aims at enhancing and optimising the employment of the distinct element method, currently confined to the analysis of local mechanisms of reduced-scale dry-joint blocky assemblies, with a view to simulate the experimentally observed responses of a series of URM full-scale specimens with mortared joints subjected to quasi-static in-plane cyclic loading. To this end, a mesoscale modelling approach is proposed that employs a simplified microscale modelling approach to effectively capture macroscale behaviour. Dynamic relaxation schemes are employed, in combination with time, size, and mass-scaling procedures, to decrease computational demand. A new methodology for numerically describing both unit, mortar and hybrid failure modes, also including masonry crushing due to high-compression stresses, is proposed. Empirical and homogenisation formulae for inferring the elastic properties of interface between elements are also verified, enabling the proposed approach to be applied more broadly. Using this modelling strategy, the interaction between stiffness degradation and energy dissipation rate was accounted for numerically. Although the models marginally underestimate the energy dissipation in the case of slender piers, a good agreement was obtained in terms of lateral strength, hysteretic response, and crack pattern.