Reduction coefficient of load carrying capacity of longitudinal members of concrete-filled steel tubular composite strut columns subjected to axial loads

The concrete-filled steel tubular(CFST) composite column in this paper is a new type of structure which is composed of four CFST members connected together by reinforced concrete(RC) plates in the main loading direction.The axially loaded specimens fail due to the crushing of RC plate near the mid-height section while the CFST longitudinal members don't reach their strengths.Therefore,the ultimate strength of CFST longitudinal members should be reduced when the superposition method is applied to calculate the axial ultimate strength of CFST composite strut column.The portion of total load carried by the CFST longitudinal members corresponding to the crushing of RC plate is derived based on the deformation compatibility equation,and the ratio of the portion of the total load resisted by longitudinal members to the ultimate strength of CFST member itself is defined as the reduction coefficient of the load carrying capacity of CFST longitudinal members in CFST composite strut column subjected to axial loads.The specified value of reduction coefficient based on different calculation theory was discussed using finite element method,and the effect of confining factor on the value of reduction coefficient was also analyzed.The results show that the reduction coefficient value is constant for various specimens with different confining factor when the unified theory is used,while the reduction coefficient from the limit equilibrium theory decreases linearly with the increase of confining factor,and the relationship can be fitted simply as a linear function.