Institute for Transportation

This report presents experimental results of modulus of rupture and shear strength tests on unsplit, green, sawn Douglas-fir lumber. Five different size-matched specimens, ranging from nominal 2- by 4-in. (standard 38- by 89-mm) to nominal 4- by 14-in. (standard 95- by 343-mm), were tested in third-point bending and five-point beam shear. A total of 120 bending and 160 shear specimens, as well as shear blocks cut from each beam, were tested. Results adjusted to 12 percent moisture content are compared with results from prior research on Douglas-fir glued-laminated timber beams. Statistical methods were used to investigate possible correlations of shear strength to beam size, shear strength to bending strength, and beam shear strength to ASTM shear block strength. The results indicate that (1) a five-point test setup can consistently produce beam shear failures over a wider range of beam sizes, (2) shear strength is dependent on beam shear area, (3) beam shear strength is related to ASTM D143 shear block strength values provided that the re-entrant corner stress-concentration effects are considered, and (4) a low correlation exists between modulus of rupture and shear strength.