Concrete masonry is traditionally built in a running bond pattern; however, the stack bond configuration is gaining popularity among architects for its distinctive aesthetic appeal. Despite this growing interest, research on stack bond masonry remains limited, with most studies concentrating on compressive behaviour, where both bonding patterns exhibit comparable performance. In contrast, the in-plane shear strength, a key parameter affected by the bonding pattern, has not been thoroughly investigated. Current design standards (i.e., CSA S304–24 and TMS 402/602–22) attempt to address this limitation by mandating a minimum amount of horizontal reinforcement to interconnect the stacked units, aiming to align their behaviour more closely with that of running bond construction. This study aims to experimentally assess the in-plane shear behaviour of masonry assemblages built in a stack pattern compared to running bond construction. The stack and running bond assemblages were identical in dimensions and grouting condition, except that the stack pattern assemblages were reinforced horizontally following standards recommendations. Eighteen masonry assemblages were constructed with dimensions of 1.20 × 1.20 m and tested under diagonal tension (shear) to assess the effects of bonding pattern, grouting, and reinforcement ratios. Furthermore, the experimental results were compared with in-plane shear strength predictions from various design standards for both bonding patterns. Additionally, compression tests on grouted and ungrouted prisms were performed to examine the compressive behaviour of each bonding pattern. The shear test results demonstrated that running bond assemblages outperformed their stack counterparts, attributed to the greater sliding shear strains concentrated along the continuous vertical head joints of the stack assemblages. Although the stack specimens incorporated horizontal reinforcement as prescribed by design standards to emulate the behaviour of running bond construction, their performance remained inferior to that of the running bond assemblages. Equations originally derived for running-bond masonry yielded shear-strength predictions in close agreement with the experimental results (except for TMS 402/602–22), with experimental-to-predicted ratios approaching unity; however, these ratios were consistently lower than those obtained for running-bond specimens and had a lower factor of safety. Both patterns exhibited almost the same compression behaviour. • Running bond showed up to 158% higher shear strength than stack bond, regardless of grouting or reinforcement. • Stack bond showed vertical cracking and higher shear strain; running bond failed mainly by diagonal cracking. • Reinforced stack bond had greater energy absorption due to sliding along vertical head joints. • Code shear equations were conservative for running bond but unconservative for stack bond.
Abdelrahman et al. (Sat,) studied this question.