Stress-Strain Behavior of C-Shaped Confined Concrete Masonry Boundary Elements of Reinforced Masonry Shear Walls

Reliable material stress-strain relationship is the cornerstone of any analysis process. Unlike reinforced concrete, limited studies focused on the stress-strain behavior of confined reinforced masonry. Reinforced masonry boundary elements (RMBEs) added at the masonry shear wall ends allow placing of at least four longitudinal reinforcement bars restrained by transverse hoops and thus introducing confinement to the wall's most stressed zone. This study presents the observed stress-strain relationship of 30 C-shaped half-scale fully grouted unreinforced and reinforced masonry boundary element specimens tested under concentric compression loading. The effect of changing hoop spacing, longitudinal reinforcement ratio, and the strength of grout on the axial stress-strain behavior of RMBE is investigated. This study quantifies and correlates the effect of these parameters on the RMBE peak stress, strain corresponding to peak, and postpeak behavior. Finally, this study investigates the capability of three existing stress-strain models in predicting the RMBE stress-strain relationship. Enhancement in both peak and postpeak stress-strain behavior were observed by decreasing the hoop spacing, increasing the longitudinal reinforcement ratio, and increasing the grout strength. The studied models overestimated the enhancement in the RMBE strength, significantly overestimated the enhancement in the RMBE strain capacity, and did not capture the postpeak stress drop. This study emphasizes the need for a new stress-strain model that can predict the RMBE response considering various confinement effects.