EDGEWISE BENDING PROPERTIES OF LAMINATED VENEER LUMBER - EFFECT OF VENEER GRADE AND RELATIVE-HUMIDITY

Effects of veneer grade and relative humidity (RH) on the edgewise ben ding properties of laminated veneer lumber (LVL) were investigated. Fi ve types (based on veneer grade composition) of LVL fabricated with ro tary-cut southern pine (loblolly pine: Pinus taeda L.) veneers of B, C , and D grades and liquid phenolic formaldehyde were destructively tes ted in edgewise bending after being conditioned and equilibrated under the environmental conditions of 65 percent RH at 75 degrees F and 95 percent RH at 75 degrees F (23.9 degrees C). All LVL consisted of 13 p lies of veneer and their layups were: LVL-1: all B grade veneer; LVL-2 : two plies of B grade veneer on both faces and all C grade veneer in the core plies; LVL-3: two plies of B grade veneer on both faces and a ll D grade veneer in the core plies; LVL-4: all C grade veneer; and LV L-5: all D grade veneer. The dimension of LVL specimens was 1.5 inches (3.8 cm) (width) by 3.5 inches (8.9 cm) (depth) by 96 inches (244 cm) (length). Also, No. 1 and No. 2 grade solid sawn southern pine lumber (loblolly) specimens with identical dimensions were destructively tes ted in edgewise bending under identical environmental conditions for c omparison of their structural performance. A significant effect of ven eer grade on the static bending strength (modulus of rupture (MOE) and stiffness (modulus of elasticity (MOE)) of LVL was observed. An incre ase of RH from 65 to 95 percent at 75 degrees F (23.9 degrees C) had a considerable weakening effect on the MOR. Reductions in MOR of 16.3 t o 23.9 percent were observed in the LVL groups; MOE reductions were 24 .7 to 32.4 percent. Effect of RH on the MOR and MOE of solid southern pine lumber was considerably less compared to LVL. The MOR values of L VL-1 (11,231 psi (77.4 MPa)) and LVL-4 (7,415 psi (51.13 MPa) were, re spectively, higher than those of No. 1 grade (10,402 psi(71.85 MPa)) a nd No. 2 grade (6,587 psi (45.42 MPa)) solid southern pine lumber. The 15th percentile values of MOR of each LVL type and solid lumber group determined from this study are to be used for the loads of duration-o f-load (DOL) tests of these groups under different environmental condi tions.