【作者】 王勇；

【导师】 陈得良； 许红胜；

【作者基本信息】 长沙理工大学 ， 结构工程， 2014， 硕士

【摘要】 随着钢管结构在土木工程中的广泛应用,圆钢管K型节点也大量的出现在桁架、网架等结构中。尽管,目前有关K型节点受力性能方面的研究已取得了大量的研究成果,但仍有许多问题并没有得到完美的解决,仍需进一步关注。近年来,对K型节点受力性能的研究主要围绕节点极限承载力的问题而展开的,而对节点疲劳寿命方面的研究相对而言较少。此外,在国家钢结构规范中有关计算节点极限承载力的公式也并未考虑边界条件的影响,整体上偏于保守。因此,本文将以圆钢管平面K型间隙节点为研究对象,主要对节点的极限承载力、破坏模式以及疲劳寿命方面的问题进行了相关研究。首先,利用有限元方法对圆钢管平面K型间隙节点的极限承载力与破坏模式进行了探讨,并应用规范公式对部分圆钢管平面K型间隙节点的承载力进行了计算。分析时主要考虑了支、主管轴线间角度θ,支、主管直径比β(d/D),主管径厚比γ(D/T)以及四种不同边界条件与加载方式对节点极限承载力与破坏模式的影响。然后,将规范公式计算结果与有限元分析结果进行了对比,并分析了产生计算偏差的原因。研究表明节点的几何影响参数θ、β、γ对节点的极限承载力与破坏模式有不同程度的影响,并且γ是影响节点破坏模式的主要参数；当β、γ较小时,边界条件对节点极限承载力的影响基本可以忽略,当β、y较大时,边界条件对节点极限承载力的影响逐渐体现出来。其次,分析了圆钢管平面K型间隙节点的疲劳寿命问题,利用了Paris公式定量反推了节点疲劳扩展阶段的剩余寿命。分析中,一方面采用有限元软件建立了含二维表面穿透裂纹标准三点弯曲试样的有限元模型,并计算了试样的应力强度因子,另一方面应用理论公式法对试样应力强度因子进行了计算。然后将有限元分析结果与理论公式计算结果进行对比,验证了建立含裂纹体模型思路及方法的合理性。最后,将借鉴上述思路与方法建立含初始表面半椭圆裂纹圆钢管平面K型间隙节点有限元模型,并将节点应力强度因子有限元分析结果通过公式换算成有效应力强度因子代入Paris公式中计算节点的疲劳寿命。分析节点的疲劳寿命时,主要考虑了支、主管直径比β,主管径厚比γ以及裂纹深度与主管壁厚比a/T对节点疲劳寿命的影响。研究表明节点的疲劳寿命随γ、a/T值的增大而减小,随β值的增大而增大；对于主管较薄或支管直径较小的节点,β、γ的影响更加明显；对于主管较薄或初始裂纹a较大的节点,a增大,节点的疲劳寿命将急剧减小。更多还原

【Abstract】 With the wide application of steel structure in civil engineering, tubular uniplanar K-joint is frequently applied to truss structure, rack structure, etc. At present, previous researches about tubular uniplanar K-joint mechanical performance have obtained a lot of achievements, but there are still many problems solved imperfectly. Hence, further attention is still needed. Besides, recently, studies on the properties of K-joint stress mostly focus on the ultimate bearing capacity of node, with little attention on fatigue life. In addition, according to the steel structure specification of state, the formulas about computation ultimate bearing capacity of nodes have not taken the influence of boundary condition into consideration, leading to conservative results. Therefore, the present study focuses on tubular uniplanar gap K-joint, and mainly investigates its ultimate bearing capacity, failure mode, and failure life.Firstly, the finite element method is adopted to study the ultimate bearing capacity and failure mode of tubular uniplanar gap K-joint, and meanwhile, the standard formula is used to calculate the bearing capacity of tubular uniplanar gap K-joint. In the present study, the influence of axis angle θ between the main pipe and the branch pipe, the diameter ratio β (d/D) of branch and main pipe, and the diameter-thickness ratio γ (D/T) of main pipe, as well as four kinds of boundary conditions and loading modes on nodes’ultimate bearing capacity and failure mode are analyzed. Besides, the ultimate bearing capacity of tubular uniplanar gap K-joint is calculated by using the standard formula, and then, the result is compared with that of finite element analysis. In addition, the causes of calculation deviation are also investigated in the present paper. Results show that the node geometric parameters θ、β and γ influence the ultimate bearing capacity and failure modes for the tubular uniplanar gap K-joint differently. Among the three parameters, y is the main parameter influencing node failure modes, and when β and γ are small, the influence of boundary conditions on the ultimate bearing capacity of nodes can be ignored, but when they are larger, the influence will show up gradually.Secondly, the fatigue life of tubular uniplanar gap K-joint is also analyzed and calculated by adopting the Paris formula. During the analysis, on one hand, the finite element software is employed to establish a two-dimensional standard finite element model of three-point bend specimens with a through crack on the surface, as well as to calculate the stress intensity factor of the specimen; on the other hand, the theory formula is also applied to calculate the stress intensity factor. And then, the finite element analysis results and the theoretical formula calculation results are compared, which shows that the crack model is reasonable. Finally, the finite element model of tubular uniplanar gap K-joint which contains an initial semi elliptical surface crack is established with the above mentioned method. The fatigue life of node is calculated by firstly obtaining the effective stress intensity factor of nodes from the finite element analysis and then plugging them into the Paris formula. In terms of the analysis of the fatigue life of nodes, the influences of the branch and main pipe diameter ratio β,and the main pipe diameter-thick ratio y, as well as the crack depth and wall thickness ratio a/T on fatigue life of nodes are focused and considered. Results show that fatigue life of nodes decreases with the increasing of y and a/T, while it increases as β increases; what’s more, as to thinner main pipes or branch pipe nodes of smaller diameter, the effects of β and y are more obvious;and moreover, as for thinner main pipes or nodes of larger initial crack a, the fatigue life of node will decrease sharply as a increases.更多还原