基于桁梁实桥试验的钢管混凝土界面传力机制

为分析钢管混凝土桁梁桥的承载性能和钢-混凝土组合作用机理，进行了桁梁上、下弦钢管混凝土界面传力行为实桥试验和全桥板壳-实体有限元参数分析；以主跨71 m的简支半穿式钢桁梁桥为依托，沿其上、下弦杆节间长度范围内共布设102个应变测点，测试并分析了加载车作用下钢管轴向应变分布和钢-混凝土界面传力特征；采用ABAQUS软件建立了试验桥板壳-实体有限元模型，经实测挠度与应变数据验证模型的可靠性后，进行了界面连接状态、界面抗剪刚度、钢管厚度、管内混凝土强度等对钢管混凝土界面传力性能的参数影响分析。分析结果表明:钢管轴向应变分布规律可反映钢管混凝土界面传力的基本特征；钢管混凝土桁架上、下弦杆节点区域均出现界面剪力不均匀分布现象，钢-混凝土界面有效传力范围内钢管轴向应变呈负指数函数分布，其他区域钢管轴向应变保持不变；完全脱黏的钢管混凝土桁架弦杆的钢管轴向应变在节点一定范围内呈二次抛物线函数分布；钢管轴向应变因界面连接状态所表现出的不同应变分布规律和剪力传递长度可用于评价钢管混凝土组合作用强弱和界面工作状态；桁架弦杆的剪力传递长度随钢管厚度和管内混凝土强度的增加而增大，钢管厚度的影响更显著；在钢管混凝土桁架弦杆内设置抗剪连接件可缩短剪力传递长度。 

Interfacial force transfer mechanism of concrete-filled steel tube based on field truss bridge test

To analyze the bearing performance of concrete-filled steel tubular truss bridge and steel-concrete composite action mechanism, the field truss bridge test on the interfacial force transfer behavior of concrete-filled steel tubes for the upper and lower chords and the finite element parameter analysis of shell and solid elements of the bridge were carried out. On the basis of the simply-supported half-through steel truss bridge with a main span of 71 m, 102 strain measuring points were arranged within the joint range along the upper and lower chords. The characteristics of axial strain distributions of steel tubes and the interfacial force transfer between steel and concrete were tested and analyzed under the action of the loading vehicle. The software ABAQUS was used to build the finite element model for the shell and solid elements of the test bridge, and the model reliability was verified by the measured deflection and strain. After that, the influences of parameters such as the interfacial connection state, interfacial shear stiffness, steel tube thickness, and concrete strength in the tube on the interfacial force transfer performance of concrete-filled steel tubes were analyzed. Analysis results show that the axial strain distribution laws of steel tubes can reflect the basic characteristics of the interfacial force transfer of the concrete-filled steel tube. The uneven distributions of interfacial shear force are shown in the joint areas of the upper and lower chords of the concrete-filled steel tubular truss. The axial strain of steel tubes at the steel-concrete interfaces within the effective force transfer range is distributed as a negative exponential function. In other areas, it remains unchanged. For the fully de-bonded chords of the concrete-filled steel tubular truss, the axial strain distribution of steel tubes is a quadratic function in a certain range of joints. As a result, the different axial strain distribution laws of steel tubes due to the interface connection state and the shear transfer length can be used to evaluate the steel-concrete composite action strength and interfacial working state between the concrete and the steel tube. The shear transfer length of the truss chord becomes longer with the increases in the steel tube thickness and strength of concrete in the tube, but the influence of steel tube thickness is more significant. Setting shear connectors in the chord of concrete-filled steel tubular truss can shorten the shear transfer length.