Comparison of Shear Modulus Test Methods

Abstract

This research compared the results of three tests: ASTM D 198 torsion, ASTM D 198 three-point bending and the five-point bending test (FPBT) using machine-stress-rated (MSR) lumber and laminated veneer lumber (LVL) to determine if the shear properties evaluated by the different test methods were equivalent. Measured E:G ratios were also compared to the E:G ratio of 16:1 commonly assumed for structural wooden members.

The average shear moduli results showed significant differences between the three test methods. For both material types, the shear moduli results determined from the two standard test methods (ASTM D 198 three-point bending and torsion), both of which are presently assumed to be equivalent, were significantly different.

Most average E:G ratios from the two material types and three test methods showed differences from the E:G ratio of 16:1 commonly assumed for structural wooden members. The average moduli of elasticity results for both material types were not significantly different. Therefore, the lack of significant difference between moduli of elasticity terms indicates that differences between E:G ratios are due to the shear modulus terms.

This research has shown differences in shear moduli results of the three test types (ASTM D 198 torsion, ASTM D 198 three-point bending, and the FPBT). Differences in the average E:G ratios per material and test type were also observed.