Evaluation of Glued Laminated Beams of Eastern Spruce and Eastern Hemlock

Full-size glued laminated beams of eastern spruce and of eastern hemlock were tested to failure to obtain initial design data for these species. The beams were 20 feet long and approximately 5 inches wide. Two beam depths (12.5 and 18 in.) were tested with the latter being included to check for a tendency to fail in shear. The study consisted of 24 spruce beams and 22 hemlock beams. For each species approximately half the beams were designed according to visual grading criteria while the remaining beams were designed utilizing machine-rated MOE data. Results for the spruce beams were affected by a fingerjoint adhesion problem, so no possible design values are being recommended at this time. Even with the fingerjoint failures, however, the spruce beams with visually graded lumber exceeded the predicted values as determined by the conventional method based on the ratio of the moment of inertia of knots to the moment of inertia of the whole cross section (Ik/Ig). For the hemlock beams, design stresses determined for MOR and MOE/ respectively were: 1,600 and 1.2×106 pounds per square inch for visually graded material; 2,000 and 1.2×106 pounds per square inch for E-rated material. The relatively low MOE values may limit the consideration of hemlock for many structural uses. Neither species exhibited shear as a primary failure.

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