Experimental study of size effect on shear-controlled hollow clay brick unreinforced masonry walls under in-plane shear-compression loading

Drift capacity of unreinforced masonry walls (URM) is a key parameter for seismic assessment and design. Although previous studies have established its dependence on wall size for flexural and hybrid failure modes, this relationship remains unclear for walls failing in shear. This study investigates how wall size influences the in-plane drift capacity of hollow clay brick URM walls in walls with shear-controlled behaviour. Six quasi-static shear-compression tests were conducted on walls of three heights (1.4 m, 2.0 m and 2.8 m), with the same aspect ratio, material properties and boundary conditions, and with two levels of compression load. Results show that small walls exhibit significantly higher drift capacity than medium and large walls, supporting previous recommendations to adopt a minimum testing height of 1.5 m when deriving drift capacities from experiments. From a mechanical perspective, the ratio of shear-to-flexural displacement was found similar across the wall sizes, indicating it is not responsible for the observed drift differences. Digital Image Correlation measurements revealed that at a given drift, crack widths were smaller in small walls, while at a given limit state, crack widths were similar across all sizes. This suggests that crack width could be used as a size-independent indicator of limit state attainment, despite the challenges associated with quantifying this parameter in certain numerical models. Future research should examine the applicability of these findings to other masonry typologies.