The southern pine species group is the main softwood resource used in the U.S, and the majority of southern pine is used in lumber production. The use of lumber in structural purpose requires feasible strength and stiffness grading method ensuring characteristics allowable stress values. The stiffness and strength of most of southern pine lumber is assessed using visual grading system. The objective of this study was to evaluate a production weighted sample of 2 × 4, 2 × 6, 2 × 8, and 2 × 10 No. 2 grade southern pine lumber collected across its geographic range. The results of this research show a snapshot of the material commercially sold in the southern U.S. region. Over one third of the specimens contained pith, and had an average mean value of 4.6 for number of rings per inch (RPI) and 43.8% for latewood (LW). The overall specific gravity (SG), modulus of elasticity (MOE) and modulus of rupture (MOR) were 0.54, 10.1 GPa, and 41.7 MPa, respectively. The allowable design bending strength (Fb) for 2 × 4, 2 × 6, 2 × 8, and 2 × 10 was 11.2, 9.2, 8.1, and 7.1 MPa, respectively. Specimens containing no pith, RPI higher or equal then 4.0, and LW higher or equal then 33.0% were greater in MOE and MOR. The effect of grading controlling characteristics of the material was also studied. The presence of knots had the most significant impact on mechanical properties. Specimens with wane and shake had greater SG, MOE, MOR, Fb values than specimens with others grading controlling characteristics. The mean values found for RPI, LW, and SG met the requirements recommended for southern pine No. 2 lumber. The MOE and Fb values found therein met the previous and the new allowable design value. The results of this research can be used to identify and to select the best variables to improve the prediction of bending properties of visually graded lumber.
|Advisor:||Seale, R. Dan|
|Commitee:||Jeremic Nikolic, Dragica, Ross, Robert J., Shmulsky, Rubin|
|School:||Mississippi State University|
|School Location:||United States -- Mississippi|
|Source:||DAI-B 79/01(E), Dissertation Abstracts International|
|Subjects:||Forestry, Wood sciences|
|Keywords:||Controlling characteristics, Grading system, Mechanical properties|
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