Measurement and prediction of lateral torsional buckling loads of composite wood materials: Rectangular sections

Differences in the elastic constant ratios and torsional rigidity between solid wood and structural composite lumber may result in differences of the lateral torsional buckling behavior of these materials. The experimental critical buckling loads (CBLs) determined from a cantilever beam test method were compared with CBL predictions based upon the load resistance factor equations for wood design and modifications to the design equations incorporating measured E:G ratios and measured torsional rigidity terms. Experimental materials included machine-stress-rated lumber, laminated veneer lumber (LVL), parallel strand lumber (PSL), and laminated strand lumber (LSL) tested at three different lengths. The current LRFD equations best predicted the CBL values for solid wood and the PSL, but predicted nonconservative CBL values for the LVL. The current LRFD equation modified to incorporate measured E:G ratios was the best predictor for the LVL and LSL materials tested and represented no improvement in CBL prediction for the solid-sawn lumber and PSL. The incorporation of the measured torsional rigidity term did not significantly enhance any of the CBL predictions. The modeling of the test specimens as isotropic materials produced more agreeable CBL predictions than use of the measured torsional rigidity values. Therefore, the current LRFD equations are verified for solid-sawn lumber and recommended for use with PSL. The LRFD equations incorporating the material specific E:G ratios are recommended for LVL and LSL to provide more accurate CBL predictions.