Improved grading system for structural logs for log homes

Abstract

Current grading standards for logs used in log home construction use visual criteria to sort logs into either “wall logs” or structural logs (round and sawn round timbers). The conservative nature of this grading system, and the grouping of stronger and weaker species for marketing purposes, probably results in the specification of logs with larger diameter than would be required if a more precise grading method were available. This study evaluated the relationships between log strength and stiffness as a basis for a mechanical grading system. A sample of 120 logs, 4.9-m (16-ft.) long, was obtained from a mixture of fire-killed subalpine fir and lodgepole pine trees. The logs were tested in bending and in compression parallel to grain. Flexural stiffness as determined by transverse vibration was found to be the best single predictor of static strength and modulus of elasticity (MOE). The proposed mechanical grading system uses a combination of MOE and visual characteristics to predict mechanical properties. The proposed system is predicted to yield a higher strength for a givenMOEvalue than does the current visual system.

Citation

Green, D.W.; Gorman, T.M.; Evans, J.W.; Murphy, J.F. 2004. Improved grading system for structural logs for log homes. Forest products journal. Vol. 54, no. 9 (2004): Pages 52-62