层积结构对加拿大铁杉三层胶合木典型力学性能的影响

The influence of lamination structure on major mechanical properties of 3-layer glulam timber made from Canadian hemlock

以锯材为基本单元的正交胶合木(cross-laminated fimber, CLT)和平行胶合木(glue-laminated timber, GLT)是具有广阔应用前景的两种胶合木。为研究层积结构不同而引起的胶合木胶合性能和力学性能差异,选用No.2加拿大西部铁杉[(Tsuga canadensis L.) Carrière]在相同制备工艺条件(胶黏剂为单组分聚氨酯胶黏剂,施胶量为160 g/m^(2);冷压时间为1 h,冷压压力为1.0 MPa)下,并在同一大幅面压机上压制尺寸为4 300 mm×1 200 mm×105 mm的三层结构CLT和GLT板。依据LY/T 3039—2018、CSA O112.10-08、ANSI/APA PRG 320-2019与ASTM D198-15等国内外标准,测试CLT和GLT的胶层剪切强度、抗弯性能和抗剪性能。结果发现:干态条件下CLT的胶层剪切强度平均值为1.17 MPa,湿态条件(浸水真空-加压循环)下则降为0.83 MPa,而干态条件下GLT的胶层剪切强度为5.59 MPa,湿态条件下则降为3.47 MPa,由降幅可判定GLT胶合质量对环境湿度变化更为敏感;CLT和GLT梁四点面外弯曲时跨中截面应变沿高度方向基本上是均匀且对称的线性分布,由此可认为这两种胶合木梁在跨高比较大时受弯变形遵循平截面假定;CLT梁的抗弯弹性模量、抗弯强度、层间剪切强度分别为10 065.84,37.86和1.96 MPa,皆小于GLT梁的抗弯弹性模量、抗弯强度和层间剪切强度;比起GLT梁,CLT梁受弯破坏模式更为复杂,包含了沿木材年轮方向的滚动剪切破坏和纵横向层板之间的胶合界面破坏。上述试验研究和分析为这两种胶合木在工程中的应用提供了设计参考和理论依据。

Made from sawn lumber, cross-laminated timber(CLT) and glue-laminated timber(GLT) are two types of engineered wood products(EWPs) with broad application prospects. The materials for both EWPs are similar, but their assembly structures are very different, namely, CLT is a panel product obtained by gluing sawn lumber components arranged in layers oriented perpendicular to each other, while GLT is composed of sawn lumber components bonded along the grain direction. However, many performance differences between both EWPs due to lamination structures have not been revealed. In order to study the differences in bonding properties and mechanical properties of CLT and GLT, Canadian western hemlock(Tsuga canadensis(L.) Carrière) Grade 2 sawn lumber specimens were selected to make three-layer CLT panels and GLT panels with a dimension of 4 300 mm(length) ×1 200 mm(width)×105 mm(thickness), using the same one-component polyurethane(PUR) resin and the same press with the same processing parameters to minimize variations. According to the standards of LY/T 3039-2018, CSA O112. 10-08, ANSI/APA PRG 320-2019, and ASTM D198-15, the bonding shear strength(BSS), bending and shear properties of CLT and GLT were examined. The results showed that the average BSS of CLT under dry condition was 1.17 MPa, which decreased to 0.83 MPa under wet condition, while the BSS of GLT under dry condition was 5.59 MPa, which decreased to 3.47 MPa under the wet condition. From the decrease, it could be believed that the bonding quality of GLT was more sensitive to the change of environmental humidity. When CLT and GLT beams were tested by the method of out-of-plane four-point bending, the cross-section strain in the middle of the span was uniformly and symmetrically linear-distributed along the height direction. Therefore, it could be considered that the bending deformation of CLT and GLT beams followed the plane section assumption with a large span-height ratio. The bending flexural modulus of elasticity, bending strength and interlaminar shear strength of the CLT beam were 10 065.84, 37.86 and 1.96 MPa, respectively, which were lower than those of the GLT beam. Compared with the GLT beam, the bending failure mode of the CLT beam was more complex, including rolling shear failure along the direction of wood growth ring and bonding interface failure between longitudinal and transverse layers. The above experimental research and analysis provided a design reference and theoretical basis for the engineering applications of these two types of EWPs.