Torsional Rigidity and Lateral Stability of SCL and I-joist Beams

Abstract

Hindman et al. (2001) presented a paper outlining the potential effects on structural performance of structural composite lumber materials with different E:G ratios compared to solid wood. This paper concluded that the torsional rigidity and lateral torsional stability of these materials may be affected by differences in the E:G ratios. Current research applied a testing protocol to measure the torsional rigidity and critical buckling loads (CBLs) of machine stress rated (MSR) lumber, laminated veneer lumber (LVL) and LVL flanged I-joists. The MSR Lumber had a higher torsional rigidity than both the LVL and LVL I-joists. CBLs of three different test specimen lengths were measured for each engineered wood material for subsequent comparison to design equations including load resistance factor design (LRFD) and modified Euler formula for performance prediction of lateral stability. The CBLs of the MSR Lumber were similar to CBLs predicted by LRFD NDS (1996) equations, while LVL values were best predicted by a Modified Euler equation. All predictions were less than the LVL I-joists measured CBLs. Further refinement of the predictions to determine the CBLs of LVL I-joists may be needed.