Calculation of ultimate load-carrying capacity of eccentrically loaded concrete filled steel tubular (CFST) columns with initial stresses

A nonlinear finite element method is presented for analyzing concrete filled steel tube(CFST) columns with initial stress subjected to eccentric load.Case study shows that the calculation results agree well with the test results.This finite element method is employed to analyze the behavior of eccentrically loaded CFST columns,taking initial stress degree,slenderness ratio,and eccentric ratio as the parameters.It is indicated that the influence of initial stress to the behavior of eccentrically loaded stub columns is almost the same with that to axial loaded columns.However,for the eccentrically loaded long columns,initial stress will make its ultimate load-carrying capacity decrease in a nonlinear tendency downwards,and the maximum descend is about 20%.Formula for predicting the initial stress reduction factor(the ratio of ultimate loads of CFST eccentrically loaded column with initial stress to that without initial stress) through an amount calculation results and adding steel strength as the fourth parameter are presented.Finally,a table of initial stress reduction factors with only two main parameters(initial stress degree and slenderness ratio) is given out to put in practice.