Unified solutions on axial compressive strength of concrete filled steel lube

Based on the twin shear unified strength theory, the load capacities of the Concrete Filled Steel Tube (CFST) under axial compression are investigated. The three restriction effect coefficients of the lateral force to the concrete, thin wall steel tube and CFST are derived respectively. The unified formula of the axial compressive strength of CFST is obtained. The results indicate that the restriction effect of intermediate principal stress is important for strength of CFST. The theoretical basis can be provided for the calculations of axial limit strength of CFST by using the results in this paper.