Axial compression behavior of square section concrete-filled steel tubes reinforced with internal latticed steel angles

The axial compression behavior of square CFSTs (concrete-filled steel tubes) reinforced with internal latticed steel angles was investigated in this study, and the test results including load-displacement and load-strain behavior, failure modes, and ultimate load were obtained. The experimental results demonstrated that the steel angles exerted an additional confining effect on the enclosed concrete, and altered the stress distributions of the adjacent concrete. The corresponding finite element model was established subsequent to the experiment, and the analysis and discussion of the axial compression mechanisms was conducted. The parametric analysis was performed to evaluate the influence of main parameters on the load-displacement behavior, and the analysis results revealed that the concrete made the highest contribution to the ultimate load. Additionally, the formulas for calculating the ultimate load were proposed according to the superposition method, and the calculation results demonstrated that the design formula derives from the unified theory of CFSTs exhibit enhanced accuracy and reduced deviation. Finally, a reliability analysis was conducted to evaluate the feasibility of the proposed design formula, and the analysis results indicated the calculated reliability index decreases with an increase in the steel ratio, and for specimens with a higher steel ratio, a lower yield strength of steel tube leads to a lower reliability index.