How should structural timber be tested for compliance?
What types of structural tests should be performed to evaluate my structural product/s?
There are 10 design properties that are assigned to a timber stress grade: Bending Strength, f’b; Bending Stiffness, MOE; Tension Strength, f’t; Compression Strength, f’c; Beam Shear, f’s; Modulus of Rigidity, G; Bearing Strength perpendicular to the Grain, f’p; Bearing Strength parallel to the Grain, f’l; Joint Shear Strength, f’sj; Tension perpendicular to the Grain, f’tp.
The first three properties are most commonly measured when evaluating a timber species’ in-grade characteristic properties, and best describe timber’s overall strength characteristics and its general relationship to other strength properties. The last four are linked to the strength group classification assigned to the timber species, and are not measured by standard in-grade testing procedures.
When first establishing in-grade strength properties, it is worthwhile to test for bending strength, bending stiffness, and tension strength. Having established these characteristic material properties, the next stage is to periodically monitor the bending strength and stiffness values. After gaining confidence that the grading process is producing timber that is meeting or exceeding the desired target strength values, then the periodic monitoring could focus on a lower number of test replications for either compression strength or beam shear strength together with bending strength and stiffness. In this manner the most important strength values are covered, while still demonstrating the assumed linkages between bending strength and remaining strength properties.
A progressive cost-effective testing program can be discussed with you and drafted to suit your mill’s compliance testing needs. Please contact us to discuss initiating or continuing with a more effective compliance testing program.
Tags: bending stiffness, compliance, compression strength, modulus of rigidity, shear strength, strength characteristics, strength properties, structural tests, structural timber, target strength, timber species