Experimental Study On The Bond Slip Stress-Strain Relationship Of Improved Composite Concrete Shaped Steel Tube

The application of improved combined shaped(L-shaped and T-shaped)concrete-filled steel tubes in actual construction projects can effectively avoid problems such as pillar fertilizer beams and protruding edges and corners in the structure,which is beneficial to increase the use area of the building.The traditional special-shaped steel pipes are formed by bending and welding of steel plates,but the processing is difficult,the binding ability is poor,and the corners are easily deformed.The improved combined shaped steel pipe is welded directly from the rectangular steel pipe and the U-shaped steel pipe to effectively avoid the above problem.The project has a wide range of application prospects.Based on the summary of domestic and foreign literature in this field,this paper adopts a theoretical analysis,combined the experimental research with finite element simulation,and focuses on the improvement of the bond-slip stress-strain relationship of the composite profiled concrete-filled steel tube concrete.It mainly includes the following aspects:(1)Based on the main parameters of steel tube thickness,steel tube length,and concrete strength grade,11 L-shaped concrete-filled steel tube concrete specimens and11 T-shaped steel tube concrete specimens were designed and manufactured.Through the launch test of 22 irregularly shaped steel tube concrete specimens,the working mechanism and failure mode of the improved composite steel tube concrete under axial pushing force were studied.The test shows that the ultimate failure load(P_u)increases with the increase of the thickness and length of the steel tube.And with the increase in the grade of concrete strength increases.(2)The relationship curve between the load(P)and the slip(S)amount at the loading end and free end of the test specimen was obtained by pushing out test,and the ultimate failure load(P_u)and the magnitude of the displacement(S_u)at the time of failure were determined.By analyzing the stress of the component,the method of measuring the bond stress between the steel pipe and the concrete is proposed,the distribution law curve of the axial strain(?(x))along the longitudinal direction of the pipe and the distribution law of the bond stress(?(x))along the length of the component are obtained.The results show that the axial strain(?(x))and the bond stress(?(x))of the steel tube have a negative exponential change before the ultimate failure load occurs.(3)The ABAQUS finite element simulation software was used to simulate and analyze the process of pushing out the test,and the curve of the relationship between load(P)and slip(S)at the load end of the special-shaped steel tube concrete specimen was obtained.Compared with the test results,the correctness of the results was verified.