脱空缺陷对圆端形椭圆钢管混凝土T形相贯节点轴压性能影响

Effects of concrete gap imperfection on axial compression behavior of CFREHS tubular T-joints

圆端形椭圆钢管混凝土在桥拱和桁架等结构中逐步被推广应用,然而由于施工工艺、服役环境和材料缺陷等不利因素,可能导致其出现脱空缺陷。为研究脱空缺陷对圆端形椭圆钢管混凝土相贯节点受力性能的影响,设计了10个圆端形椭圆钢管混凝土T形相贯节点并进行节点的支管加载轴压性能试验,研究脱空率、相贯类型和主支管径比等参数对其在支管轴压荷载下破坏模式、承载力、刚度和延性的影响,揭示了节点域应变分布规律和典型受力特征,并基于组件法和节点破坏机理,提出考虑脱空缺陷影响的圆端形椭圆钢管混凝土T形相贯节点支管受压的承载力计算方法。结果表明:脱空缺陷的存在会削弱圆端形椭圆钢管混凝土T形相贯节点的承载力和刚度,并随着脱空率的增大,节点的承载力和刚度持续减小;由于脱空缺陷和支管轴压荷载影响,带脱空缺陷圆端形椭圆钢管混凝土T形相贯节点可能出现支管受压屈曲、主管脱空区局部凹陷和主管挠度过大等破坏现象;提出的理论计算方法可准确预测带脱空缺陷圆端形椭圆钢管混凝土T形节点在支管受轴力作用下的承载力。

The concrete-filled round-ended elliptical hollow steel(CFREHS) tube have been gradually applied for bridge arches and truss structures in recent years, while concrete gap imperfections may be observed in these composite members due to the disadvantages resulted from the construction process, the service environment and the material defects. In order to explore the effects of gap imperfections on the performance of CFREHS tubular T-joints, ten CFREHS tubular T-joints were designed in this study. The effects of various parameters including the concrete gap ratio, joint intersection type and brace/chord diameter ratio on the failure patterns, axial load bearing capacity, stiffness and ductility were analyzed, and the strain distribution rule and typical loading characteristics were revealed. The calculation models on the axially loading partition of steel brace and the flexural resistance of CFREHS chord were established based on the component method and failure mechanism of the joints. The design formulae for assessing the axial load bearing capacity of CFREHS tubular T-joints were presented considering the influence of concrete gap imperfections. The results indicate that the concrete gap imperfections would impair the axial load bearing capacity and stiffness of the CFREHS tubular T-joints, and the axial load bearing capacity and stiffness of the joints decrease with the gap ratio. Because of the effects of concrete gap imperfections and axial forces, the failure modes of this type of tubular joints include local buckling of brace, inward buckling of chord and the excessive deflection of chord. The design formulas can predict the axial load bearing capacity of the CFREHS tubular T-joints with concrete gap imperfections properly.