Investigation of the Girth Size and intervals Effect on Lateral Buckling Strength of Built-up Double I & C-Sections Columns

Steel composite columns with parallel girth are one of the common types of columns used in steel structures in the country (IRAN). Despite many studies on the behavior of these columns, the impact dimensions and spacing of girth on the buckling load of these columns have been less considered. In addition to resistance criteria, in designing of pressure members, the stability criteria must also be considered. In other words, the pressure members of a structure will be defeated effectively by local buckling before reaching maximum compressive strength or influence of buckling phenomenon. The local buckling is one of the common instability of structural members and is an important factor in design of the Built-up columns, so the buckling phenomenon of these columns must be strongly controlled. In this research, 10 columns by double I sections and 6 columns by double C sections were analyzed by different intervals of girths. All column sections are double IPE140 or UNP140. Dimensions of the girth in double I sections are 100×180 mm, with thickness of 4, 6 and 8 mm, by intervals axes to axes 400, 600 and 800 mm in both side. Dimensions of the girth in double C sections are 100×140 mm, with thickness of 4 and 6 mm, by intervals axes to axes 400, 600 and 800 mm in both side. Finally, the elastic buckling load of these columns was obtained by using the Abacus finite element software and compared with the relationships in the tenth chapter of the National Building Regulations.