In-Plane Cyclic Behavior Analysis of Masonry Walls Strengthened with Ultra-High-Performance Concrete

Unreinforced masonry walls (URM) exhibit poor energy dissipation capacity, limited tension-carrying capacity, and rapid stiffness degradation under cyclic loading. This study develops a three-dimensional numerical model in Abaqus to evaluate the effectiveness of ultra-high-performance concrete (UHPC) overlay in improving the in-plane cyclic performance of URM walls. A simplified micro-modelling technique was adopted, along with the Drucker-Prager criterion for masonry units, the concrete damage plasticity model for UHPC, and a surface-based cohesive behavior for masonry joints. The URM wall and UHPC material models were validated separately against published experimental and numerical results. Following validation, double-layer stretcher-bond URM walls were strengthened with UHPC overlays and analyzed under in-plane cyclic loading to investigate the effects of UHPC thickness and UHPC-masonry interface behavior, considering cohesive interaction to capture bond degradation and possible debonding, and tie-interaction to simulate perfect bonding. The results showed that a perfectly bonded 40 mm-thick UHPC overlay enhanced the structural load capacity and energy dissipation capacity to 6.9 and 1.5 times those of the URM wall, respectively, while reducing the residual drift ratio by 10%. When the UHPC thickness was increased from 15 mm to 50 mm, the lateral load capacity and energy dissipation capacity increased to 3 and 1.7 times the corresponding values of the 15 mm-thick overlays, respectively, while the residual drift ratio changed minimally.