Effect of Several Drying Conditions on Strength of Coast-Type Douglas-Fir Timbers

Four-inch-thick Douglas-fir timbers were air-dried, kiln-dried, and organic-vapor-dried to determine: honeycomb development in timbers dried in xylene vapors, comparative rate of kiln-drying 4-inch material at 150? and 200?F., and effect of various drying conditions on certain strength properties of timbers. Honeycomb developed in timbers kiln-dried at 200?F. as well as those vapor-dried at 220?F. Honeycomb was so extensive that considerable cutting was required to obtain small clear specimens for testing. Strength properties of Douglas-fir timbers were reduced 15 percent due to high (202?F.) temperatures. Modulus of elasticity was affected least while work to maximum load was affected most. Air-dried timbers were 39 percent stronger in bending than were green timbers. Kiln-drying 4-inch Douglas-fir timbers to 16 percent moisture content required 50 percent more time at 150?F. than was needed at 200?F.

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