Axial Compressive Performance of L-Shaped High Strength Grouting Material Filled Square Steel Tube

[Purposes] This research is conducted to solve the problems of the low applicable height of ordinary concrete-filled steel tubular special-shaped columns and the easy separation of steel tube and concrete at the internal corner. [Methods] Three concrete-filled square steel tubular columns were welded to form an L-shaped composite special-shaped column, and ultra-high-strength grouting material with standard compressive strength greater than 100 MPa was used in the composite L-shaped columns. The influences of different grouting material strengths and steel tube wall thicknesses on their axial compression performances were studied through experiments. [Findings] The results show that the axial compression bearing capacity of composite L-shaped columns with ultra-high-strength grouting materials is 92%-170% higher than that of pure steel L-shaped columns. With the increase of the strength of high-strength grouting materials, the restraining effect of steel pipe on high-strength grouting material decreases, and the ductility of the specimen increases. The wall thickness of the steel pipe increases from 4 to 6 mm, which can effectively prevent local buckling. The failure mode of the component changes from buckling failure to bending deformation, and the ductility of the specimen increases by more than 50% on average. By comparing the results of the axial compression bearing capacity test with the results obtained from the axial compression bearing capacity calculation formula in 8 current codes at home and abroad, the calculated value obtained by using the specification AISC 360 is the closest to the test result. The research results can improve the axial compression bearing capacity and ductility of the composite special-shaped columns, improve the problem that the steel tube and concrete are easily separated at the internal corners, and help the application and promotion of ultra-high-strength grouting materials in the structure of concrete-filled steel tube special-shaped columns.