Applicable equivalent bow imperfections in GMNIA for Eurocode buckling curves – SHS, RHS and welded box sections

The direct resistance check using advanced numerical models is spreading among designers nowadays. Therefore, the development of accurate and up-to-date design rules supporting the FEM-based design of slender steel structures is an important task and prospective research field. Using the direct resistance check, the load carrying capacity of the steel structure under investigation is obtained as a result of geometrical and material nonlinear analysis using imperfections (GMNIA). The present paper investigates the imperfection magnitudes of slender steel columns and specifies the accurate value of the equivalent geometric imperfection to be applied for welded square, cold-formed and hot-rolled square (with rounded corners), and rectangular sections. Using the proposed imperfection magnitude, the load carrying capacities can be determined by GMNI analysis and the obtained results will be identical or very close to the buckling resistances calculated by the buckling curves of the Eurocode. The developed imperfection magnitude is given in closed form as a function of relative slenderness, steel strength and buckling curve parameter (imperfection factor α). Details on the determination of the necessary equivalent geometric imperfection and the obtained trends on the flexural buckling resistance are presented in the current paper.