In this paper, concrete filled steel tubes columns (CFT) are investigated by using finite element program ANSYS 15.0. Analysis are done for four different shapes of columns (circular, square,hexagonal andoctagonal). Results of analytical solution (for circular and square) were compared with existing experimental data provided by [Alwash et al., 2013].Comparative resultsof failure load give 4% difference between experimental and ANSYS 15.0. Also, parametric studies have been carried out to investigate the effect of concrete filled steel tubes columns shapes (for hexagonal and octagonal) on load carrying capacity.Finally, a newformulaefor predicting the ultimate strength of CFT is proposedbased on experimental data of 148 CFT columns of different cross sections with side length ranging between 200 and 4000 mm. To check the validity of the proposed equation, the loads calculated from the designmethods (American Concrete Institute (ACI 318M-14), Eurocode (EC4),New Zealand Standard of concrete structures(NZS) and American Institute of Steel Construction (AISC)) are used to compare with it. The comparison shows least convergence percentageof the proposed equation.