Load-carrying capacity of axially loaded concrete-filled steel tubular columns made of thin tubes

Abstract An experimental investigation was conducted on 30 CFST columns. An influence of the following factors on load-carrying capacity of the investigated columns was analyzed: the column slenderness ( λ 1  = 42, λ 2  = 27 and λ 3  = 15), the tube thickness (the reinforcement ratio was equal to 4% or 6%), the way of applying the load to CFST columns (through the concrete core or through the entire cross-section), the bond strength between a steel tube and a concrete core. The results of the experimental investigation let the author derive a practical method of determining load-bearing capacity of CFST columns. The Eurocode 4 provisions regulating composite steel and concrete structures design impose the minimum share of a steel tube in the cross-sectional area of a CFST column. This minimum share is the prerequisite for the Eurocode 4 to be applicable. It ranges from 0.5% to 6%. As the experimental research presented in the paper indicate, the CFST columns of such low reinforcement ratios can be also effective in carrying loads. The proposed method is a second order analysis based on stiffness, similarly as the calculation procedure for the ordinary reinforced concrete columns which is used in Eurocode 2. The experimental results prove the author's suggestion to be correct.