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.) timbe rs, 3 m (10 ft.) long, sampled from two mills in the South. Dynamic mo dulus of elasticity (MOE) was also obtained using pulse echo stress wa ve techniques. The results suggest that currently assigned allowable b ending strength, compressive strength, and MOE values are appropriate for Select Structural and No. 2 visual grades. The relationship betwee n bending strength and compressive strength parallel to the grain was found to be similar to that for standard 38-mm- (nominal 2- in.-) thic k dimension lumber A significant relationship was found between pulse echo MOE and static bending properties and between specific gravity an d static bending properties. We conclude that there are no technical b arriers to the development of a mechanical grading system for structur al timbers. Such a system would provide more precise assignment of all owable properties and thus allow better utilization of the forest reso urce. However, new grading and duality control procedures would have t o be developed and approved before mechanical grading of timbers could be conducted under the American Lumber Standard system.