矩形钢管K型节点复合型应力强度因子计算方法研究

相比圆形钢管桁架，矩形钢管桁架在施工方面具有一定的技术经济优势，并已广泛应用于桥梁工程中，鉴于断裂力学法评估该类结构疲劳性能的需要，该文探讨矩形钢管K型节点在支管拉压平衡荷载作用下的应力强度因子计算方法。提出带表面裂纹矩形钢管K型节点有限元建模方法，并与试验进行验证；通过参数分析，研究节点和裂纹几何参数对节点几何修正系数Y的影响；多元回归分析拟合得到矩形钢管K型节点应力强度因子计算公式及其修正后的设计计算公式，并通过算例分析给出基于断裂力学的钢管节点剩余疲劳寿命评估方法。结果表明：有限元结果与试验结果比值均值为1.012，变异系数为0.034，两者最大差值仅为5.5%，表明有限元计算结果可靠；节点几何参数2γ、τ与Y呈正相关，θ与Y呈负相关，其原因主要在于节点相贯线处刚度和受拉荷载变化，改变了裂纹尖端应力场，从而影响了裂纹扩展速率，裂纹几何参数c/a与Y呈正相关，但影响不明显，a/t₀与Y呈负相关；提出的应力强度因子计算公式与有限元计算结果吻合良好，且修正后用于设计的计算公式具有95%的可靠度；圆形钢管节点应力强度因子高于矩形钢管节点，平均提高24.9%，说明在相...

STUDY ON CALCULATION METHOD FOR EQUIVALENT STRESS INTENSITY FACTOR OF RECTANGULAR HOLLOW SECTION K-JOINTS

Compared to the trusses with circular hollow sections, the trusses with rectangular hollow sections have both technical and economic advantages on the aspect of construction, therefore they are widely used in the bridge engineering. In terms of the demand on the fatigue assessment of this sort of structures based on fracture mechanics method, the calculation method for stress intensity factor of rectangular hollow section K-joints under basic balanced loadings is studied. The finite element model for a rectangular hollow section K-joint with surface crack is developed and validated with test results. Then, the influence of joints and weld parameters on the geometrical correction factor Y is evaluated through parametric analysis. The equation of stress intensity factor of rectangular hollow section K-joints is proposed through multiple regression analysis and, then it is modified for design purpose. Additionally, a case study is conducted to present the fatigue residual life assessment method for hollow section joints based on fracture mechanics. The research results show that the mean value of finite element results to test results is 1.012 with the variable coefficient of 0.034. The maximum difference between these two results is just 5.5%. It indicates that the finite element model is reliable. It also shows that the joint geometrical parameters 2γ and τ correlate with Y, while θ negatively correlates with Y. The reason is due to the change of joint stiffness and of tensile loading, which changes the stress field at crack tip and crack propagation rate. The weld geometrical parameter c/a correlates with Y, while a/t₀ negatively correlates with Y. It should be noted that the influence of c/a on Y is not obvious. The proposed equation of stress intensity factor can agree well with the finite element results, and the modified equation for design purpose has the reliability of 95%. The stress intensity factors of circular hollow section joints are greater than the rectangular hollow section joints with an average increase of 24.9%. It demonstrates that the crack propagation rate of circular hollow section joint is faster compared to the rectangular hollow section joint under the same loading conditions. The case study further demonstrates this conclusion that the fatigue residual life of a circular hollow section joint is 2.1×105 cycles, which is lower than a rectangular hollow section joint with the fatigue residual life of 2.3×105 cycles.