Structural Behavior of Masonry Beams with Alternative Shear Reinforcement

Shear reinforcement, or stirrups, for reinforced masonry beams made of concrete blocks are placed inside the cells of the units. Since it is a requirement by masonry standards for shear stirrups to hook around the longitudinal reinforcement, the placement of conventional steel rebar as shear reinforcement in 200 mm (8 in.) or narrower masonry beams becomes challenging. Even the smallest size steel rebar available in Canada [10M or 11.3 mm (0.44 in.) actual diameter rebar], a standard hook detail is difficult for a mason to accommodate within field construction conditions. Hence, the current study investigated two different alternative shear stirrup configurations, namely, the use of 8-mm (5/16 in.) diameter smooth steel bars and the use of commercially available repurposed bed joint wire reinforcement. The current study showed that the masonry beams with the alternative stirrup details exhibited similar ductility as the masonry beam built with conventional steel rebar. The beam containing the bed joint wire as shear stirrups enhanced the capacity of the beam slightly more than the beams with conventional rebar and with the 8 mm (5/16 in.) smooth bar. Most importantly, the use of bed joint wire as shear reinforcement reduced crack width in a similar manner as the conventional rebar. In addition, the study found that the Canadian and American standards overestimated the shear strength of narrow masonry beams. The present study also found that the directionally based strength reduction factor (Chi factor, χ) recommended in the Canadian design standard is overly conservative.