钢管混凝土K形节点足尺模型疲劳性能试验

为研究钢管混凝土K形节点足尺模型疲劳性能，对其进行疲劳试验，并与钢管K形节点疲劳性能进行比较，通过对比分析得到钢管混凝土K形节点热点应力分布规律、疲劳性能演化和疲劳破坏形式，并探讨钢管混凝土K形节点疲劳寿命评价方法。结果表明：钢管混凝土K形节点与钢管K形节点最大热点应力的位置均位于受拉支管与主管相贯焊缝主管侧冠点处，钢管混凝土K形节点的应力集中系数约可降低至钢管K形节点的58%，且热点应力宜采用二次外推方式；两者疲劳性能演化过程均可分为疲劳裂纹萌生、扩展和破坏三个阶段，钢管混凝土K形节点在扩展和破坏阶段分别以沿主管壁厚方向和相贯焊缝长度方向扩展为主，与钢管K形节点主要扩展方向相反；两者疲劳裂纹均属于张开型Ⅰ裂纹，钢管混凝土K形节点疲劳裂纹断口沿壁厚方向呈“呲牙”状，且疲劳裂纹扩展路径较长。钢管混凝土K形节点抗疲劳性能明显优于钢管K形节点的最主要原因在于，管内混凝土的约束作用提高了钢管混凝土K形节点主管的径向刚度，钢管混凝土K形节点的压陷和外凸变形远小于钢管K形节点。基于一点法原则建立的钢管混凝土K形节点疲劳设计S-N曲线具有较高精度。

Fatigue performance experiment of full-scale model of concrete-filled steel tubular K-joint

To compare with the fatigue performance of circular hollow section (CHS) K-joint, fatigue test on full-scale concrete-filled steel tubular (CFST) K-joint model was conducted, and distribution of hot spot stress, fatigue performance evolution and fatigue failure mode of CFST K-joint were acquired by comparative analysis. Furthermore, the evaluation method used on fatigue life of CFST K-joint was discussed. It is found that the location of the maximum hot spot stress of CFST K-joint is the same as that of CHS K-joint, namely the crown point of chord and tensile brace intersection welding seam near chord intersecting line, but the stress concentration factor of CFST K-joint decreases to about 58% of that of CHS K-joint, and its extrapolation method tends to change in a parabolic form. Although fatigue performance evolution of both of them can be divided into three stages including initiation, extension and failure of fatigue crack, the main extension direction of CFST K-joint fatigue crack is along the chord thickness and the length of the welds in the latter two stages, respectively, which distinguishes from that of CHS K-joint. Meanwhile, both of them have the same fatigue crack type, namely opening Class I crack, and the fatigue fracture of CFST K-joint along the chord thickness acts as ‘teeth’, whch makes the extension path longer than that of CHS K-joint. Radial stiffness of the chord of CFST K-joint is improved by combined action of concrete filled in the chord, which makes concave and convex deformation along the diameter of the chord much less than that of CHS K-joint under axial loads, and it is the main reason why the fatigue performance of CFST K-joint is superior to CHS K-joint. S-N curve for fatigue design of CFST K-joint established by the one-point method has a higher accuracy.