云杉-松-冷杉层板钉接木受弯性能试验研究

Experimental investigation into bending performance of nail-laminated timber fabricated with spruce-pine-fir

层板钉接木(nail laminated timber,NLT)是将木材层板在宽面叠合钉接制成的一种工程木产品,相比于胶合木,NLT具有成本低、工艺简单等优点。通过对层板和NLT板的受弯性能进行研究,可以实现合理设计NLT。为此,分别对云杉-松-冷杉(spruce-pine-fir,SPF)层板及由该层板制成的NLT板进行静力试验,分析层板和NLT板的破坏模式与力学性能指标,并基于正态概率分布模型与材料抗力分项系数,计算层板和NLT板弯曲弹性模量和抗弯强度的标准值和设计值。结果表明:层板和NLT板的典型破坏模式均为木材受拉破坏,其中层板为脆性破坏,而NLT板则为层板依次受拉开裂,破坏较缓慢,其荷载-挠度曲线呈阶梯型下降。相比于层板,NLT板弯曲弹性模量和抗弯强度的平均值变化不明显,但标准值和设计值明显提高;NLT板弯曲弹性模量和抗弯强度的标准值分别为8.326 GPa和26.4 MPa,相比于层板的分别提高了22.4%和80.8%;NLT板抗弯强度的设计值为15.2 MPa,相比于层板的提高了76.7%。

Nail-laminated timber(NLT)is fabricated by nailing the wood lamination together through the wide faces.Compared with glue-laminated timber(GLT)and cross-laminated timber(CLT),NLT avoids the use of adhesive,thus simplifying the fabrication and reducing the cost.To compare the bending performance of NLT and provide design basis,bending tests were carried out on both the spruce-pine-fir(SPF)lamination and the NLT specimens fabricated with SPF lamination.The failure modes and mechanical properties of the lamination and the NLT specimens were analyzed.The characteristic and design values of the lamination and the NLT specimens were calculated based on the normal probability distribution model and the material performance factors.The results show that under bending,tension failure is the typical failure mode for both the lamination and the NLT.The failure of the lamination is in a brittle mode.However,the failure of the NLT specimens become more gradual with the successive cracking of the lamination.The ladder type failure is presented in the load-deflection curve of the NLT.The average modulus of elasticity and the average bending strength of the NLT do not change significantly compared with the lamination.However,the characteristic and design values of the NLT increase compared with the lamination.The characteristic modulus of elasticity and the characteristic bending strength of the NLT are 8.326 GPa and 26.4 MPa,which are 22.4%and 80.8%higher than those of the lamination,respectively.The design bending strength is 15.2 MPa for the NLT,which is 76.7%higher than that of the lamination.