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.