Strength and structural safety of long-span light wood roof trusses

Seventy-five light wood roof trusses were tested to failure in order to evaluate their safety and serviceability, and to examine the effects of size (members and spans) and load distribution (balanced and unbalanced) on truss performance. Two spans were tested: 21 m (45 trusses) and 12 m (30 trusses). It was found that the trusses were not consistent in their ratios of failure load to design load. Failures in the low-strength trusses included shear in the heel region of the top chord and tension in the scarf-cut bottom chord. It was subsequently demonstrated that these weaknesses could be removed through improved heel detailing. Key words: wood, trusses, strength, stiffness, safety, truss plates.