Influence of Geometric Curvature on the Out-Of-lane flexural capacity of Unreinforced Masonry Walls.

Abstract

Unreinforced masonry (URM) remains a prevalent construction system in Uganda and numerous regions worldwide, yet its susceptibility to out-of-plane (OOP) loading continues to precipitate some of the most abrupt and severe structural failures. Existing analytical frameworks and design provisions are predominantly based on straight, planar walls, leaving curved wall configurations, ubiquitous in both architectural practice and vernacular construction, insufficiently characterized within prevailing theory. This study interrogates the combined influence of geometrical configuration and material properties on the flexural resistance of URM walls subjected to OOP loading. Laboratory characterization of locally manufactured clay bricks and selected mortar mixes revealed pronounced variability in stiffness relative to compressive strength, reflecting heterogeneous microstructural features and production inconsistencies. While augmented mortar strength enhanced compressive performance, its effect on unit-mortar interface friction remained marginal, highlighting persistent limitations in bond behaviour. These empirically derived parameters were incorporated into a finite element model developed in ABAQUS and validated against published experimental benchmarks and mathematical metrics, successfully reproducing crack initiation, stiffness degradation, and ultimate failure mechanisms. Parametric analyses revealed that straight walls exhibit predominantly bending-dominated responses, wherein improved mortar grades elevate load capacity without altering the governing failure mode. Conversely, curved walls manifested fundamentally distinct structural behaviour: increasing projection distance markedly improved OOP strength and initial stiffness through the development of compressive thrust lines and an enlarged effective lever armphenomena not adequately captured by classical plate theory. Geometry-induced arching conferred performance gains even for lower-grade mortars, whereas higher-grade mortars accentuated this effect, albeit with reduced ultimate displacement. Using projection height as a practical geometric descriptor, a simplified expression is proposed to estimate the flexural capacity of curved URM walls, providing an accessible alternative to full numerical modelling. Collectively, the findings underscore wall geometry as a dominant, geometry-driven resilience mechanism operating synergistically with material enhancements, challenging the conventional reliance on planar bending theory for predicting URM OOP behaviour.