Properties and grading of southern pine timbers

Bending and compression parallel-to-the-grain tests were conducted on approximately 200 dry southern pine 140- by 140-mm (6- by 6-in.) timbers, 3 m (10 ft.) long, sampled from two mills in the South. Dynamic modulus of elasticity (MOE) was also obtained using pulse echo stress wave techniques. The results suggest that currently assigned allowable bending strength, compressive strength, and MOE values are appropriate for Select Structural and No. 2 visual grades. The relationship between bending strength and compressive strength parallel to the grain was found to be similar to that for standard 38-mm- (nominal 2- in.-) thick dimension lumber. A significant relationship was found between pulse echo MOE and styptic bending properties and between specific gravity and static bending properties. We conclude that there are no technical barriers to the development of a mechanical grading system for structural timbers. Such a system would provide more precise assignment of allowable properties and thus allow better utilization of the forest resource. However, new grading and quality control procedures would have to be developed and approved before mechanical grading of timbers could be conducted under the American Lumber Standard system.