榫头局部正交层板结构对直榫节点受力性能的影响

Effects of Locally Cross-Laminating in Tenon on the Structural Performance of Straight Tenon and Mortise Joints

【目的】针对直榫节点受弯时榫头横纹变形较大、刚度和承载力较弱的问题,将“正交胶合木”概念引入直榫节点中,探讨榫头局部正交层板结构对直榫节点受力性能的影响,并提出合理的直榫节点“预增强”方法和参数为传统榫卯节点在现代木结构工程中的应用提供理论与技术支持。【方法】以花旗松普通层板胶合木为材料,设计制作18个足尺直榫节点试件,其中部分试件榫头不作处理(对照组),其他试件榫头加工成正交层板结构。通过节点抗弯试验分析直榫节点的破坏模式和工作曲线,计算得到节点的抗弯刚度和极限弯矩;提出复杂应力状态下的木材本构关系模型,建立直榫节点有限元模型,对其抗弯性能进行模拟。与试验结果对比并验证模型准确性后,基于模型对局部正交层板结构直榫节点进行参数分析,探讨正交层板厚度、宽度等参数对直榫节点受力性能的影响规律。【结果】对照组直榫节点主要破坏模式为榫头端部顶面和根部底面的局部横纹压缩变形,局部正交层板结构可有效缓解榫头横纹压缩变形。与对照组相比,4组不同局部正交层板结构直榫节点的抗弯刚度平均值提升14.0%~36.9%,而极限弯矩有升有降;数值分析结果与试验结果吻合良好;随正交层板宽度增加,直榫节点的抗弯刚度先升后降,而承载力先降后升;随正交层板厚度增加,直榫节点的抗弯刚度呈上升趋势,而承载力呈下降趋势;对本研究直榫节点,建议正交层板厚度与榫头厚度比值取0.25,宽度取210 mm。【结论】局部正交层板结构可提高直榫节点的抗弯刚度,通过合理选择参数还可提高直榫节点的承载力;采用强度和韧性较好的材料,如重组竹和钢板等替代木材层板,可进一步提高直榫节点的抗弯刚度和承载力。

【Objective】Based on the fact that the local compression deformation of straight tenon and mortise joints under bending is relatively large and the bending stiffness and load bearing capacity are low,the concept of“cross-laminated timber”was referenced to develop suitable pre-reinforcing methods for straight tenon and mortise joints.This study was carried out to investigate the effects of locally cross-laminating on the structural performance of straight tenon and mortise joints,and put forward a reasonable pre-reinforcement methods and relevant parameters in order to provide theoretical and practical supports for the application of traditional tenon and mortise joints in modern timber structure projects.【Method】18 straight mortise and tenon joints were manufactured with glulam of No.1 Douglas fir(Pseudotsuga menziesii)lamination,of which some were treated with 4 different reinforcing methods.All of the joints were tested under monotonic loading.The failure modes and working curves were observed,and the moment carrying capacity and initial stiffness were obtained.The constitutive model of wood under complex stress state was developed and finite element(FE)model was developed.The tests were simulated by FE methods and the model was verified by comparing the predicted deformation modes,load-displacement curves,moment and stiffness with the test results.Then parametric study was conducted to investigate the effects of locally cross laminating on the structural performance of the straight tenon and mortise joints.【Result】It was observed that compression deformation perpendicular to grain at the upper surface near the tenon end and the lower surface near the beam was the most critical for the untreated tenons.By locally cross laminating,the compression deformation perpendicular to gain could be effectively reduced.It was found that the initial stiffness of the joints increased from 14.0%to 36.9%for different reinforcing configurations,and the moment carrying capacity of some specimens increased while some specimens decreased.The predicted results from FE model were correlated well with the test results.With the increase of width of the cross-laminations,the stiffness of the joints firstly increased and then decreased,however,the moment presented an opposite trend.With the increase of thickness of the cross-laminations,the stiffness of the joints increased while the moment decreased.For the tenon and mortise in this study,it was recommended to take a rate of thickness of cross-lamination to the tenon width of 0.25 and a width of 210 mm as the optimum solution,respectively.【Conclusion】The rotational stiffness of straight tenon and mortis joints could be improved by the locally cross laminating.By choosing appropriate parameters,the ultimate moment could also be increased.The structural performances of the straight tenon and mortise joints could be further improved by using materials like bamboo scrimber and steel plates,which might have a higher strength and ductility,instead of wood laminations.