竹集成材自攻螺钉拉穿性能试验

Experimental study on the pull-through performance of self-tapping screws in laminated bamboo

对竹集成材-自攻螺钉连接试件进行单轴拉穿加载试验,探究自攻螺钉在竹集成材中的拉穿性能及破坏形态,为自攻螺钉连接设计与工程应用提供基础数据。依据EN 1383-2016木结构试验方法设计8组64个竹集成材-自攻螺钉连接试件,比较竹集成材不同纹理方向和板厚对初始刚度、极限荷载、屈服荷载及延性等影响。试验结果表明:竹集成材自攻螺钉连接试件在节点处的力学性能主要由板材厚度决定,而纹理方向的影响较小。钉节点的破坏形态与竹集成材纹理方向密切相关。自攻螺钉在竹集成材中拉穿破坏形态的横纹弦向和横纹径向存在两种破坏现象,分别为竹集成材表面陷落破坏与整体劈裂破坏。当试件纹理方向相同时,板厚与极限荷载和初始刚度呈现正相关;当试件板厚相同,在横纹弦向上承载能力高于横纹径向。当竹结构满足最小尺寸设计要求时,对于直径6 mm的半螺纹自攻螺钉从横纹弦向钉入板厚30 mm的竹集成材,此时试件拉穿承载性能和延性达到最佳状态,充分发挥了材料的力学性能。

In recent years, various composite engineered bamboo materials have been developed at domestic and abroad as important building material. Laminated bamboo(LB) has a higher strength-to-weight ratio than other engineered bamboo materials. Self-tapping screws are widely used in bamboo-wood structures because of the superior mechanical properties and ease of assembly. Uniaxial pull-through loading test on specimens with LB and self-tapping screws connections. To investigate the pull-through properties and damage patterns of self-tapping screws in LB and to provide essential data for designing and utilizing self-tapping screws connections. Eight sets of 64 specimens were designed according to the standard of EN 1383-2016 to compare the effects of different grain directions and plate thickness on the initial stiffness, ultimate load, yield load and ductility of bamboo composite materials. The test results showed that the mechanical properties of the bamboo-integrated timber self-tapping screw-connected specimens at the nodes were mainly determined by the thickness of the panels. At the same time, the grain direction had less influence. The damage pattern of the node was closely related to the grain direction of the bamboo composite material. There were two kinds of damage phenomena in the cross-grain chordal and cross-grain radial directions: surface trap damage and overall splitting damage of the bamboo composite material. When the specimens had the same grain directions, the plate thickness was linearly related to ultimate load and initial stiffness. The ultimate load and initial stiffness increased with the increased plate thickness. When the specimens have the same plate thickness, the load carrying capacity is higher in the transverse chord direction than in the transverse radial direction. The mechanical properties of the material were fully utilized. In practice, an 6 mm diameter semi-threaded self-tapping screw was used to nail the laminated bamboo from the cross-grain chord direction from a board thickness of less than 30 mm, where the load-bearing properties and ductility are optimal and the mechanical properties of the material can be fully exploited.