SHEAR-STRENGTH OF SOLID-SAWN DOUGLAS-FIR BEAMS

The objective of this study was to improve current shear design criter ia 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 val id correlation between shear strength and beam size for solid-sawn mat erial; and determining whether shear strength is more dependent on she ar 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, rangin g from 38 by 89 mm (2 by 4 in.) to 38 by 337 mm (4 by 14 in.), were te sted in five-point beam shear. ASTM D143 shear block miners were cut a nd tested from each beam. Results adjusted to 12% moisture content wer e 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 st rength to beam size and beam shear strength to ASTM shear block streng th. Results indicate that (1) a five-point test setup can consistently produce beam shear failures over a wide range of beam sizes; (2) shea r strength is dependent on beam shear area; and (3) beam shear strengt h is related to ASTM D143 shear block strength values provided the ree ntrant corner stress-concentration effects are considered.