Bending Properties of Laminated Lumber with the Same Modulus of Elasticity Composed of Several Softwoods with Different Thicknesses of the Elements

In the present study, bending properties (modulus of rupture (MOR), modulus of elasticity (MOE), bending work (W), and Janka plastic modulus (Z)) were investigated for 4-ply and 3-ply laminated lumber composed of softwoods with different thicknesses of the elements. In 4-ply laminated lumber, sugi (Cryptomeria japonica D.Don) elements were used for the inner 2 layers, and hinoki (Chamaecyparis obtusa Sieb. et Zucc.) or karamatsu (Larix kaempferi Carriere) laminas were used for the outermost 2 layers. In 3-ply laminated lumber, a sugi element was used for the inner 1 layer, and hinoki or karamatsu laminas were used for the outermost 2 layers. Elements and laminas were graded by dynamic modulus of elasticity and then laminated for manufacturing the laminated lumber with the same MOE. Although the MOE was almost the same value in all laminated lumber members, significant differences in MOR, W, and Z were recognized among the types of laminated lumber. In addition, W was affected by the bending property (W) of species laminated at the outermost layers. On the other hand, Z was affected by the bending property (Z) of species laminated at the inner layers. In all types of laminated lumber, W and Z were mainly affected by deflection at the plastic region. When laminas and elements without finger joints were used, bending properties of 4-ply and 3-ply laminated lumber were almost the same as those of 10-ply laminated lumber.