Experimental investigation of axial compressive behavior of square and rectangular confined concrete-masonry structural wall boundary elements

Reinforced masonry boundary elements (RMBEs) are critical components in determining the lateral response of reinforced masonry structural walls with boundary elements. Fundamental interpretation of the effect of various influential parameters on the RMBEs ' behavior is essential to enhance their stress-strain response. This study investigates, experimentally, the influence of various design parameters and construction procedures on the axial compressive behavior of fully grouted RMBEs built with C-shaped concrete-masonry blocks. Thirty-eight unreinforced and RMBEs were constructed and tested under concentric axial loading till failure. The effect of five parameters, namely, the vertical reinforcement ratio, the volumetric ratio of confinement reinforcement, crosssection configuration, stack pattern and running-bond, and pre-wetting of dry masonry shell before grouting, was investigated. The test results showed that increasing the vertical reinforcement ratio of the RMBEs resulted in a significant increase in the peak compressive stress and a considerable reduction in the corresponding strain ductility. Moreover, as the RMBEs volumetric ratio of transverse reinforcement doubled, the strain ductility witnessed a remarkable enhancement, whereas the peak compressive stress experienced an inconsistent trend. RMBEs built with rectangular C-shaped cross-sections exhibited comparable peak stress, smaller drop following the face shell spalling, and better strain ductility than square RMBEs. The running-bond pattern had a negative effect on both the peak stress and the strain ductility of dry RMBEs, although it exhibited comparable or even enhanced response in wet RMBEs compared to those built in the stack pattern. Pre-wetting of dry masonry shell before grouting was found to boost the peak compressive stress of unreinforced and RMBEs significantly. However, it adversely affected their strain ductility. Wet RMBEs showed a steeper post-peak descending branch compared to their dry counterparts. Indeed, the vertical reinforcement ratio and pre-wetting of dry masonry shell were the most critical parameters affecting the RMBEs peak compressive stress, whereas the confinement ratio mostly influenced the strain ductility. This study sheds light on the most critical parameters influencing the stress-strain components (i.e., strength and ductility) of RMBEs.