Full-scale test behavior of cold-formed steel roof trusses

Ten full-scale roof trusses fabricated from cold-formed steel channel sections were tested to ultimate capacity under concentrated panel point loading. As the test program moved forward and failure modes became manifest, various practical means of increasing truss capacity were investigated. While gusset plates at the heel connections in bearing were a significant factor in strength determination, local buckling of the top chord adjacent to the heel plates was the predominant failure mechanism. Trusses that experienced this local buckling failure exhibited postbuckling ductility, whereas failures at the connections in hearing were sudden. A truss was subjected to partial point loading to simulate the effect of a partial roof snow load and the experimental ultimate capacity substantiated the predicted capacity. A beam-column analysis of the top chord in the region where failure Occurred was performed in accordance with the requirements of the Canadian Standards Association CSA S136-01. The calculated nominal resistance was 12% conservative as compared to the experimental ultimate capacity of the truss. The trusses were sufficiently stiff to satisfy a deflection requirement of the span length (L) divided by 360.