Simplified analysis on concrete enclosure for composite circular columns in axial compression

According to the assumption that constraint force for core concrete and annular tensile force in enclosed concrete is balance, theoretic minimum thickness and stirrup reinforcement ratio for axial compressive composite circular columns reinforced by enclosed concrete subjected to secondary load are deduced. And based on the section stain analysis, simplified calculation method for bearing capacity of enclosed concrete and enclosed longitudinal steel in ultimate state is established, which provides theoretical analysis basis for design and calculation for axial compressive composite circular column.