Axial compression performance of concrete-filled-steel tube flat columns with a large steel ratio

To prevent columns protruded from the inside wall, concrete-filled steel tube flat columns (CFSTFCs) with a large steel ratio were proposed in this study by limiting the sectional width and increasing the sectional height. The influence of the aspect ratio and thickness of the steel tube on the axial compression performance of CFSTFCs was investigated by axial compression tests for 12 CFSTFCs. The test results showed that two different failure modes, including a horizontal buckling ring with welding seam fracture and overall instability with local buckling in the sectional height direction, occurred in the tests. The axial load-carrying capacity and axial deformation ductility of CFSTFCs were enhanced with increasing thickness of the steel tube under the same aspect ratio. However, the axial deformation ductility of CFSTFCs gradually decreased with increasing aspect ratio. Furthermore, the Mander and Han Linhai confined concrete models were used to simulate the in-filled concrete in CFSTFCs to analyze the confinement effect from steel tube to in-filled concrete in CFSTFCs. Finally, the tested ultimate axial load-carrying capacity of CFSTFCs was compared with the different specifications to acquire the design method of CFSTFCs.