Exposure Effects Upon Performance of Laminated Veneer Lumber and Glulam Materials

Parallel laminated veneer lumber (LVL) has demonstrated tensile strengths comparable to structural lumber but with far lower variance, thus allowing higher design values. These properties have made LVL an ideal material for the tension laminations of glulam beams. This study was undertaken to study the deterioration of Douglas-fir LVL and solid-sawn glulam specimens following accelerated exposure. LVL and solid-sawn laminated specimens were tested for glueline shear strength, tension perpendicular-to-the-glueline strength, and percentage of delamination prior to and following exposure to a vacuum-pressure soak-dry schedule. The solid-sawn material exhibited higher dry strengths than the LVL but following exposure the materials differed only slightly in strength. Measurement of the percentage of delamination revealed that the solid-sawn glulam had twice the amount of splitting/separating found in the LVL. Finite-element analyses of the moisture-induced strains in the laminated materials revealed that failure of the solid-sawn sections could be caused by the variation of ring angle between laminations. The LVL was judged to be more stable than the solid-sawn material as indicated by its low incidence of delamination and high retention of glueline shear and tensile strengths.

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