Flexural behavior of concrete-filled circular CFRP-steel tube with flange-sleeve joints

The concrete filled circular CFRP-steel tube arch formed by pasting carbon fiber reinforced polymer (CFRP) on the outer side of the concrete filled steel tube has higher bearing capacity and stiffness, and can be used for tunnel support under adverse geological conditions such as high stress, extremely soft rock, strong mining, and fault fracture zones. This article proposes a new type of flange-sleeve joint, which is used for concrete filled circular CFRP-steel tube arch in tunnel engineering. The influence of different flange thicknesses (20 mm, 30 mm, 40 mm) on the failure mode, flexural bearing capacity of concrete filled CFRP-steel tube joint under four-point bending was experimentally studied. The results show that the failure mode of the specimens is CFRP axial delamination, and the flange-sleeve joint is intact, indicating that this connection method is effective; When the flange thickness is 20 mm, the bending bearing capacity and stiffness of the specimen are basically the same as those of the node free specimen, and the bending bearing capacity and stiffness increase with the increase of flange thickness. Based on ABAQUS finite element analysis, a comparison was made with experimental results, and parameterized analysis was conducted using flange thickness, casing length, and casing wall thickness as variables. The finite element results indicate that the cohesive zone model can effectively simulate the delamination process of CFRP; The thickness of the flange has a significant influence on the mechanical properties of the joint, while the length and wall thickness of the sleeve have a relatively small influence on the mechanical properties of the joint; For specimens with a steel tube diameter of 140 mm and a CFRP thickness of 3 mm, it is recommended to take a flange thickness of 20 mm, a sleeve length of 200 mm, and a sleeve wall thickness of 5.5 mm.