Strength Properties of Low Moisture Content Southern Pine

Contemporary engineering design practices in the United States require information on the strength of lumber for moisture contents as low as 4 percent. Efficient design of experimental studies on lumber properties at low moisture contents requires a better understanding of the basic mechanisms controlling moisture-property relationships. Studies were conducted on the effect of moisture content on strength and stiffness in tension and compression parallel and perpendicular to grain, and centerpoint bending. The test specimens were cut from commercially dried lumber and sorted into matched groups based on specific gravity. One group was saturated with water and four groups were equilibrated to 4, 8, 12, and 18 percent moisture content prior to testing. The results show that strength and stiffness properties are a function of both moisture content and density. Although properties generally increased with a decrease in mois­ ture content, tensile strength parallel and perpendicular to the grain reached a maxi­ mum at about 12 percent moisture content. Further drying caused significant loss in tensile strength. Empirical models are presented for predicting the effect of moisture content on tensile strength parallel and perpendicular to grain, bending, compression parallel and perpendicular to grain, and shear parallel to grain.