Bending creep performances of three-ply cross-laminated woods made with five species

Abstract

To improve the performance of cross-laminated woods, 30 types of three-ply parallel-laminated and cross-laminated woods were prepared from five species with various densities and shear compliances in cross section, and their bending creep performances were investigated on the basis of our previous research in cross-laminated wood made with sugi (Japanese cedar). The creep deformation perpendicular to the grain was decreased by cross laminating. The creep deformation perpendicular to the grain of parallel-laminated woods (P_⊥ type), that perpendicular to the grain of face laminae of cross-laminated woods (C_⊥ type), and also that parallel to the grain of face laminae of cross-laminated woods (C_║ type) tended to decrease with increasing density of species used for perpendicular-direction lamina. It was found that the extent of the decrease was greater in creep deformation than in initial deformation. The degrees of anisotropy for both deformations of laminated wood were markedly decreased by cross laminating. The extent of the decrease was much greater in creep deformation than in initial deformation and considerably smaller in buna with higher density than in sugi with lower density. The measured values of initial deformation and creep deformation of C_⊥ type were almost equal to the calculated values obtained from the measured values of parallel-laminated woods, whereas the measured values of both deformations of C_║ type were much greater than their calculated values and increased markedly with increasing shear compliance in cross section of perpendicular-direction lamina used for core. The ratios of the average of measured values to the calculated value of C_║ type ranged from 1.05 (katsura) to 1.50 (sugi) in initial deformation and from 1.30 (katsura) to 3.69 (sugi) in creep deformation. This result can be explained as the effect of deflection caused by shear force.