Exploring the effects of further drying on the tensile capacity of kiln-dried lumber

• Published in: Forest products journal Vol. 43; no. 1; pp. 25 - 32
• Main Authors: Eskelsen, V. (Oregon State Univ., Corvallis, OR), Galligan, W.L, Shelley, B.E, Peterson, J
• Format: Journal Article
• Language: English
• Published: Madison, WI Forest Products Society 01.01.1993
• Subjects: Applied sciences; BOIS DEBITE; CONTENIDO DE HUMEDAD; Exact sciences and technology; Experiments; Forest products industry; Hypotheses; Laboratories; MADERA ELABORADA; Mechanical properties; Mechanical woodworking and drying; MODELE; MODELOS; Polymer industry, paints, wood; SECADO; SECADORAS; SECHAGE; SECHOIR; Studies; TENEUR EN EAU; Test methods; Wood; Wood. Paper. Non wovens; Mechanical properties; Wood; Experimental study; Drying oven; Tensile strength; Drying
• ISSN: 0015-7473; 2376-9637

Some current models for the relationship between moisture content (MC) and strength of lumber predict a decrease in ultimate tensile stress with a decrease in MC below approximately 15 percent. One model, in American Society for Testing and Materials (ASTM) D 2915-84, predicts an increase. The models predicting a decrease were based on tests performed on visually graded lumber that had been dried slowly in the laboratory. Commercially kiln-drying to a target average MC of 12 percent can produce a moisture gradient within the outer zone with an MC as low as 7 percent. The experiment reported herein tests the hypothesis that if the outer zone has had an irreversible strength loss because of the low MCs attained during kiln-drying, further in-service drying to similar MCs would produce no additional strength loss. To this end, machine stress-rated Douglas-fir 2 by 6 specimens that had been kiln-dried on a commercial schedule to a target of 12 percent were further dried at room temperature to about 8.5 percent and then tested in tension. Results were compared with those for controls not dried beyond the commercial schedule. Further drying resulted in significant loss in ultimate tensile capacity (UTC) between the 10th and 60th percentiles. In the lower tail of the distribution, of most significance in establishing allowable stresses, loss in UTC was much less pronounced. The control data were adjusted to the further-dried (8.5%) data by each of three moisture-ultimate tensile stress models to examine model effectiveness in predicting the observed change in UTC that accompanied further drying. The Green-Evans model best fit the main part of the distribution, the ASTM D 1990-91 model best fit the lower tail, and the ASTM D 2915-84 model provided the poorest fit