Shear Strength of Solid-Sawn Douglas-Fir Beams

Abstract

The objective of this study was to improve current shear design criteria by establishing a test method for creating a database of beam shear strength of solid-sawn Douglas-fir lumber and correlating it to shear block test results; verifying whether the beam-size equation is a valid correlation between shear strength and beam size for solid-sawn material; and determining whether shear strength is more dependent on shear area, volume, or depth for modeling purposes. Experimental results are presented for 160 shear strength tests on unsplit, green, sawn No. 2 or better Douglas-fir lumber. Five different size specimens, ranging from 38 by 89 mm (2 by 4 in.) to 38 by 337 mm (4 by 14 in.), were tested in five-point beam shear. ASTM D143 shear block minors were cut and tested from each beam. Results adjusted to 12% moisture content were compared with prior research on southern pine and Douglas-fir glued-laminated timber beams. Statistical methods of censored statistics and regression investigated the following possible correlations: shear strength to beam size and beam shear strength to ASTM shear block strength. Results indicate that (1) a five-point test setup can consistently produce beam shear failures over a wide range of beam sizes; (2) shear strength is dependent on beam shear area; and (3) beam shear strength is related to ASTM D143 shear block strength values provided the reentrant corner stress-concentration effects are considered.