Parametric Evaluation of Interface Properties for Simplified Micro-Modelling of Masonry Walls

This study presents a systematic numerical investigation of hollow clay brick masonry wall panels using a simplified micro-modelling approach in which mortar joints are not modelled as separate solid layers. Instead, the joints are represented by surface-based cohesive zone models (CZM) governed by traction–separation relations. The main objective is to clarify, from a user-oriented perspective, how variations in key interface parameters influence the in-plane response of vertically perforated masonry walls. To this end, a one-factor-at-a-time parametric strategy was adopted to isolate individual effects. The interface normal and shear stiffnesses (Knn, Kss, Ktt), maximum normal traction capacity (tn), cohesion (c), friction coefficient (μ), and Mode I–II fracture energies (GIC and GIIC) were varied independently within predefined ranges while all other properties were kept constant. In total, 25 finite element models were analyzed. Hollow brick units were modelled in three dimensions with their actual geometry to preserve the discontinuous contact condition at the bed joints. The nonlinear response of the units was described using a concrete damaged plasticity (CDP) model previously calibrated for the same material system. Results were assessed through global performance indicators (peak load, displacement at peak load, stiffness, and energy dissipation capacity) together with stress, damage, and interface slip (CSLIPEQ) distributions at the peak load. The analyses indicate that parameters governing shear transfer along the joints play a dominant role in the structural response and strongly control the initiation, spread, and localization of interface slip bands. In contrast, parameters associated with the normal direction lead to relatively limited changes under the considered loading condition. Fracture energies mainly regulate the softening rate and damage evolution, therefore controlling the post-peak regime; in combination with frictional resistance, they shape the transition toward more localized or more distributed failure mechanisms. Overall, the study provides a practical cohesive modelling framework to interpret interface-parameter effects, guide model calibration, and support sensitivity assessments for hollow brick masonry systems modelled with simplified approaches in commercial finite element software.