Finite Element Model for Predicting Modulus of Elasticity of Lumber Measured by Stress-Grading Machines

Development of a finite element model to predict modulus of elasticity of lumber as measured by bending-type stress-grading machines is discussed. The model is general in that lumber characteristics critical in machine grading, such as natural bow and local stiffness variations, can be taken into account. Simulations are carried out to compare the performance of two constant deflection machines employing different testing geometries. Results show that, depending on support conditions, grading machines may vary substantially in their ability to locate low stiffness zones along the length of lumber and identify the value of modulus of elasticity at these zones. Ability of the grading machines to test end portions of the lumber is also discussed, along with the influence of span on machine accuracy