Torsional and Bending Behavior of Wood Beams

Two representative species are selected for experimentation-Douglas fir and Red oak. Ten circular and 10 square beams are tested. First, eight beams are loaded to a specified load within the elastic region under the following load conditions: (1) pure torsion; (2) pure bending; (3) bending and restrained torsion; and (4) bending and unrestrained torsion. Following these nondestructive tests, all 20 beams are loaded to failure under different loading conditions. The experimental results are in close agreement with the theoretical predictions. No appreciable change exists in the magnitude of normal stresses due to restrained or unrestrained torsion when compared to the normal stresses due to flexure only. Unrestrained torsion does not cause significant warping of the cross section of the beam. Analysis of test results for the 20 specimens that were loaded to destruction indicates that the ultimate moment and the ultimate torque are independent of each other. For the specimens tested, the presence of torsion does not appear to change the bending strength of a wooden beam.