The aim of this study was to predict the withdrawal resistance of a screw in hybrid cross-laminated timber (CLT) composed of two types of lamina layers. A theoretical model to predict the withdrawal resistance was developed from the shear mechanism between a screw and the layers in hybrid CLT. The parameters for the developed model were the withdrawal stiffness and strength that occurs when a screw is withdrawn, and the penetration depth of a screw in layers of a wood material. The prediction model was validated with an experimental test. Screws with two different diameters and lengths (Ø6.5 × 65 mm and Ø8.0 × 100 mm) were inserted in a panel composed of solid wood and plywood layers, and the withdrawal resistances of the screws were evaluated. At least 30 specimens for each group were tested to derive the lower 5th percentile values. As a result, the developed model predictions were 86–88% of the lower 5th percentile values of hybrid CLT from the properties of the lamina layer. This shows that the withdrawal resistance of hybrid CLT can be designed from the properties of its layer.
This study was performed to analyze the mechanical properties of tropical hybrid cross-laminated timber (CLT) with bamboo laminated board as the core layer in order to evaluate the possibility of its use as a CLT material. Bamboo board was used as the core layer and the tropical species Acacia mangium willd., from Indonesia, was used as the lamination in the outer layer. The modulus of elasticity (MOE), modulus of rupture (MOR), and shear strength of the hybrid CLT were measured according to APA PRG 320-2018 Standard for Performance-Rated Cross-Laminated Timber. The results show that the bending MOE of the hybrid CLT was found to be 2.76 times higher than SPF (Spruce Pine Fir) CLT. The reason why the high MOE value was shown in bamboo board and hybrid CLT applied bamboo board is because of high elasticity of bamboo fiber. However, the shear strength of the hybrid CLT was 0.8 times lower than shear strength of SPF CLT.
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