Behavior of concrete filled steel tubular beam-columns under eccentric loading of unequal end-moments

Based on a numerical constitutive model of concrete filled steel tubes, a layer method was applied and a fiber model based on partial sinusoidal curves for concrete filled circular steel tubular (CFST) columns was proposed. Utilizing the relationship between the curvature of the least favorable section and sinusoidal amplitude, a FORTRAN program was developed, and the behavior of CFST columns under eccentric loading of unequal end-moments was analyzed. The analysis results are in good agreement with the experimental results in the literature. The influences of significant parameters, such as steel ratio, yield strength of steel, strength grade of concrete, the slenderness ratio and eccentricity ratio, on the equivalent column length coefficient curves and the equivalent moment coefficient curves were discussed by using equivalent column length coefficient method and equivalent moment coefficient method, respectively. The shortcomings in the existing Chinese specification of the equivalent coefficient were pointed out. Through parameter analysis, a practical calculation formula for the equivalent column length coefficient for the beam-columns under eccentric loading was proposed. Reliability of the design method was validated by the test results of 79 specimens from the country and abroad.