Test Study on Axial Compression Behavior of GCFST Columns Under Unidirectional Repeated Load

Geopolymer concrete is one of the directions of green development in the construction industry, and casting geopolymer concrete inside steel tubes can effectively play the respective advantages of both. In order to study the axial compression performance and failure mechanism of geopolymer concrete-filled steel tubular (GCFST) columns, two hollow steel tubular columns were designed as the control group and eight geopolymer concrete-filled steel tubular columns were tested in axial compression with concrete strength grade, length-to-diameter ratio, and steel tube wall thickness as parameters. The load–displacement curve, skeleton curve, and stiffness degradation curve of each specimen were obtained by observing the force process and failure mode of each specimen, analyzing the characteristic load, and characteristic displacement, stiffness degradation, ductility, and energy dissipation capacity, and deriving the method of calculating the axial compression load-bearing capacity of GCFST columns, and comparing with several codes commonly used in the world. The results show that the length-diameter ratio has a significant effect on the failure mode of GCFST columns. The peak load and initial stiffness of each group of specimens are different, but their load–displacement curves, skeleton curves, and stiffness degradation trend are the same. The increase of geopolymer concrete strength and steel tube wall thickness can improve the ultimate load-bearing capacity, average compression capacity, and energy dissipation capacity of GCFST columns. The axial compression load-bearing capacity calculation formula proposed in this paper is in good agreement with the test results, and the calculated values of the formula are compared with the calculation results of the international codes to verify the accuracy and applicability of the axial compression load calculation formula proposed in this paper, and the results of the study can provide reference for the theoretical research and engineering application of geopolymer concrete-filled steel tube composite structure.