Predicted and Actual Performance of Two Laboratory Stress-Grading Machines Employing Different Support Conditions

Actual performance data were developed on two laboratory stress-grading machines differing only in support conditions for comparison with theoretical predictions from a finite element model developed previously. Performance was assessed on the basis of the ability of the grading machines to measure modulus of elasticity on lumber containing natural bow and one ideal defect (notch). Theory and observation were in good agreement in showing that performance of grading machines is dependent on support conditions, especially regarding their ability to identify zones of lower stiffness along the lumber. Practical implications of the results on future machine stress-rating procedures are discussed