自攻螺钉钉入角度对钢板-正交胶合木节点剪切性能的影响

Effects of the Penetration Angle of Self-Tapping Screw on Shear Performance of Steel Plate Cross-Laminated Timber Joints

【目的】探究斜螺钉连接钢板-正交胶合木(CLT)节点的抗剪切承载性能以及钢板-CLT节点通过自攻螺钉连接的破坏模式和受力机理,分析螺钉钉入角度对剪切强度、刚度的影响规律,为新型连接件的开发和应用提供理论模型和科学依据。【方法】以花旗松为试验材料,使用国产全螺纹自攻螺钉,自攻螺钉主轴与钢板所成夹角作为变量,角度分别为75°、60°、45°,螺钉钉帽偏向钢板受拉方向为拉-剪受力(T-S),螺钉钉帽偏向钢板受压方向为压-剪受力(C-S),参考美国标准(ASTM D1761-12)以1 mm·min^(-1)的速度匀速加载,观察并记录节点受力情况、破坏过程中所达最大荷载、钉子变形情况以及木材破坏特征。【结果】拉-剪和90°剪切受力模式,钉子破坏模式皆为一侧自攻螺钉被剪断。压-剪受力模式,在45°受力模式下钉子出现3种断裂方式;在60°、75°受力模式下一侧自攻螺钉产生2个明显的塑性铰,另一侧自攻螺钉在距离钉帽8 mm处被剪断。对于承载力,拉-剪状态下承载力随角度减小逐渐增大,压-剪状态下则相反;拉-剪状态下的刚度随角度减小逐渐增大。【结论】拉-剪状态下45°、60°、75°节点的承载力分别为90°的1.46、1.35、1.22倍且高于压-剪状态,刚度分别为90°的3.58、2.42、2.08倍且高于压-剪状态,其中75°的能量耗散最大。

【Objective】This study was carried out to explore the shear bearing capacity of an oblique screw connecting steel plate and CLT joint,to explore the failure mode and force mechanisms of steel plate and CLT joints connected by self-tapping screws,and to analyze the influences of angle on shear strength and stiffness.The development and application of new connectors would be expected to provide theoretical models and scientific bases.【Method】Using Douglas fir as the study object and domestic full-threaded self-tapping screws as materials,the included angle between the main shaft of the self-tapping screw and the steel plate,those were 75°,60°and 45°,respectively,was selected as the variable.The screw cap pulled in the tensile direction of the steel plate was shear force(T-S:tensile-shear),and the compression direction of the screw cap toward the steel plate was the compressive-shear force(C-S:compressive-shear).Referring to the American Standard(ASTM D1761-12)and loading at a constant speed of 1 mm·min^(-1),the stress of the node,the maximum load reached during the failure process,the deformation of the nail and the failure characteristics of the wood were observed and recorded.【Result】For T-S and 90°shear force mode,the failure modes of nails were both that one side of the tapping screw was sheared.For C-S mode,the nail had three fracture modes under the 45°force mode,whereas the self-tapping screw on the one side produced two obvious plastic hinges and that on the other side was sheared at a distance of 8 mm from the nail cap under the 60°and 75°force modes.The bearing capacity under the T-S state increased gradually with the decreasing angle,and the opposite was observed under the C-S state;the stiffness under the T-S state increased gradually with the decrease of the angle.【Conclusion】The bearing capacity of 45°,60°and 75°joints under T-S state is 1.46,1.35 and 1.22 times that of 90°,respectively,all higher than those of C-S state.The stiffness of 45°,60°and 75°joints under T-S state is 3.58,2.42 and 2.08 times that of 90°,respectively,and all higher than those of C-S state,of which the energy dissipation of 75°is the largest.