A NEW 3D-ADAPTIVE DISCRETE INTERFACE FOR MODELING THE TORSION BEHAVIOR OF MASONRY CONTACT JOINTS

The numerical modelling of the torsion behaviour of masonry block joints represents a key aspect for the assessment of the out-of-plane response of masonry walls. However, it repre-sents a challenging computational issue due to the high non-linear coupling between the tor-sion and other internal forces (shear, bending moment and axial load), meaning the necessity to use complex 3D non-linear constitutive laws. The limit analysis-based approaches represent efficient and reliable numerical tools to predict the ultimate torsion load including the interaction with shear and bending moment. Within this framework, few researchers have proposed and experimentally validated continuous and discrete contact models, able to predict the ultimate strength of masonry contact joints. These models are successfully employed to develop high-detailed simulations of 3D dry-jointed masonry block structures subjected to lateral in-plane and out-of-plane actions. Nonetheless, the limit analysis is not able to characterize the non-linear response of masonry walls prior to collapse and to predict the evolution of plastic damage and the ductility resources, if available. Aiming at overcoming such a limit, this paper introduces a new 3D adaptive discrete interface, able to simulate the non-linear torsion-shear behaviour of masonry joints. The interface consists of four springs whose orientation is updated during the analysis, following an incremental iterative Newton-Raphson algorithm taking into account the current position of the torsion centre of the interface. The ultimate torsion-shear capacity domain obtained by the proposed model is compared with limit-analysis predictions and experimental data available in the literature. The results highlight the ability of the new interface to effectively reproduce the non-linear behaviour and the ultimate strength of joints subjected to different loading combinations