Out-of-Plane Behavior of Reinforced Stack Pattern Tall Masonry Walls

Abstract

Load-bearing masonry is widely used in North America, offering architects various unit patterns, including running bond and stack bond, for both architectural and load-bearing purposes. However, stack pattern masonry in load-bearing walls faces additional design restrictions compared to running bonds. Many prefer stack patterns for their aesthetics but are often unaware of the structural limitations. These constraints originate from research on unreinforced or ungrouted stack pattern walls, with the misconception arising when horizontal reinforcement or continuous grouting is used. Thus, stack pattern walls may end up, after engineering design, being significantly weaker in flexure than running bond pattern walls. Hence, the primary objective of this study is to investigate the structural behavior of stack pattern and running bond pattern tall masonry walls under constant axial and varying out-of-plane loading. Three running bond patterns and three stack pattern reinforced concrete block masonry walls, each 4.0 m tall ×2.4 m long ×0.19 m thick, were tested under combined out-of-plane bending and axial loading. The test data showed that the failure modes of stack pattern and running bond pattern walls are similar. This study found that the out-of-plane flexural capacity of the stack pattern wall is 8% to 11% lower than the counterpart running bond wall. However, the postcracking behavior of the stack pattern and counterpart running bond walls were found to be similar. Findings from this research suggest that changes to both Canadian Standards Association (CSA) S304 and TMS 402/602 provisions regarding stack pattern masonry are warranted. Load-bearing concrete masonry construction, a popular choice in North America, offers architects the flexibility of using different unit patterns for both structural and aesthetic purposes. One common pattern is the stack bond, favored for its visual appeal. However, stack pattern masonry walls have historically faced more design restrictions than those in a running bond pattern. Hence, this study aimed to investigate the structural behavior of tall masonry walls in both stack and running bond patterns under varying out-of-plane load and constant axial load. Testing six concrete block walls, three in each pattern, the results revealed that both types exhibited similar failure modes. The study found that the out-of-plane flexural capacity of stack pattern walls was only 8% to 11% lower than that of running bond walls, while their postcracking behavior remained comparable. These findings suggest the need for revisions to current masonry design codes [Canadian Standards Association (CSA) S304 and TMS 402/602] concerning stack pattern masonry under out-of-plane behavior. We hope that the upcoming Canadian design standard CSA S304 will be updated based on the findings of this study. Such updates can better inform architects and builders when choosing between these patterns, ensuring both structural integrity and aesthetic appeal in construction projects.