double i shape column nonlinear behavior in existing steel structures

in iran, for column design, double i shape section is used due to lack of ipb profile. double i shape column performance is ambiguous in existing steel structures, especially when subjected to seismic loading. in this paper, double i shape column behavior is evaluated with 3d nonlinear analyses. monotonic behavior of 6 specimens and hysteretic behavior of other six specimens have been simulated. half of specimens have been welded ordinarily simulating constructional habit of iranian site welding and six other specimens have been welded ideally with complete manner. finally behavior of two groups of specimens has been compared in the view of the following parameters such as bending and axial strength, stress concentration and collapse mechanism.