Geometric curvature in the out-of-plane flexural design of unreinforced masonry walls
The out-of-plane behaviour of unreinforced masonry (URM) walls is commonly assessed using formulations developed for planar elements, despite the widespread use of curved masonry in architectural and historical structures. This study investigates the influence of geometric curvature and mortar properties on the out-of-plane flexural response of URM walls through an integrated experimental-numerical framework. Material characterization revealed substantial variability in locally manufactured clay bricks, with elastic modulus exhibiting coefficients of variation of up to 77%. Increasing mortar grade enhanced masonry prism compressive strength by a range of 71% (2.08-3.56 MPa), increased elastic modulus more than sixfold (360-2595 MPa), and produced an approximately 23-fold increase in normal interface stiffness. A validated ABAQUS simplified micro-model accurately reproduced experimental behaviour, achieving a normalized root mean square error of 10% and a Pearson correlation coefficient of 0.945, confirming predictive reliability. Parametric analyses showed that increasing mortar strength enhanced the peak pressure resistance of planar walls by approximately 150% (1.2-3.0 kPa), whereas the corresponding increase in highly curved walls was limited to approximately 50% (5.2–7.8 kPa). In contrast, increasing wall projection from 0 to 1000 mm enhanced yield moment capacity by 352%, 226%, 149%, and 167% for M2, M4, M6, and M12 mortars, respectively, demonstrating that geometric curvature exerts a substantially greater influence on flexural performance than material strength. Highly curved walls also exhibited increased initial stiffness and sustained moment development beyond crack initiation, indicating enhanced post-cracking reserve capacity. Analysis of the effective section modulus revealed a strong exponential dependence on wall projection (R2 = 0.96). The findings demonstrate that conventional plate theory systematically underestimates the flexural resistance of curved URM walls and establish geometric curvature as the dominant parameter governing their out-of-plane structural response.