Behavior of circular concrete-filled steel tubular columns with different end moment ratios: Modelling and discussion

Abstract

This paper develops a nonlinear model for the analysis of circular CFST columns under equal and unequal end moments using fiber beam element (FBE) method. An iterative process adopting Newton’s method combined with secant method was proposed to improve the calculation efficiency. A test database was collected to assess the accuracy of the proposed model regarding the prediction of axial load-bearing capacity, deflection curves and load–deflection curves. The verified model was then further used to investigate the behavior of CFST columns under different end moments. It was found that the normalized sectional locations of maximum deflection of CFST columns are only significantly affected by the end moment ratio, whereas those of critical sections are also influenced by the axial load. The specimen with a larger end moment ratio, steel strength, L/D ratio and/or a smaller e1/D ratio, D/t ratio experiences more significant second order effect. The bending stiffness of CFST columns is hardly affected by the end moment ratio. Moreover, the current codes, i.e., EC4 and AISC 360, may underestimate the capacities of CFST columns under unequal end moments.