Study of the influence of geometric imperfections and residual stresses on the stability of steel columns subjected to axial compression

Steel columns are known to provide strength, durability, flexibility, and greater speed of construction. Although being industrially produced under rigorous quality control, steel columns usually present small geometric imperfections and residual stresses that arise during the manufacturing process. These imperfections and residual stresses play a major role on the columns` final compressive strength. Acknowledging the complexities and high cost involved in experimental investigation of these effects, this research was geared towards assessing the influence of the geometric imperfections and residual stresses on the strength of steel columns subjected to axial compression. For this purpose, computational models of I-beam steel columns were developed and analyzed using the Finite Element Method. Initially, a linearized elastic buckling analysis was carried out to determine the critical loads (eigenvalues) and buckling modes (eigenvectors). Following this, nonlinear analyses were conducted considering materially and geometrically nonlinear effects to evaluate the column’s strength considering the geometric imperfections with different amplitudes and the shape of the first buckling mode. The elastoplastic model without hardening was adopted to represent the material nonlinearity. Finally, nonlinear analyses were carried out considering different levels of residual stresses for each geometric imperfection amplitude. The results show that the geometric imperfections and residual stresses have a strong influence on the load carrying capacity steel columns leading to a column curve close to the curve adopted by NBR 8800:2008. Therefore, both geometric imperfections and residual stresses should be properly considered in advanced analysis procedures for steel structures.