Effect of Unit Bonding Patterns on the Structural Performance of Loadbearing Concrete Block Masonry Beams

Abstract

Loadbearing concrete block masonry construction in North America is generally designed by engineers as a 50% running bond pattern. However, in some situations an architect opts for a stack pattern (or stack bond) unit coursing, not realizing that there are structural implications to this choice. The lack of research in the area of the structural effects of a unit bonding pattern has led to inconsistent and sometimes very punitive requirements for loadbearing masonry design in North America. This paper presents the results of an experimental study on 12 concrete block masonry beams with depths of two, three, and four courses to study the structural effects of a unit bonding pattern. Beam stiffness, crack patterns, deflection profiles, and ultimate strengths are presented and discussed. Using a stretcher unit with approximately 50% of the web height removed to permit grout continuity demonstrated no significant difference between running bond and stack pattern unit coursing. This evidence supports changes to current Canadian design requirements to include stack pattern masonry beams with this unit configuration. This evidence may also be considered to support the adoption of more stringent recommendations in current American design requirements.