Stiffness reduction method for the design of steel columns and beam-columns

A stiffness reduction approach is presented in this paper, which utilises Linear Buckling Analysis (LBA) and Geometrically Nonlinear Analysis (GNA) in conjunction with developed stiffness reduction functions for the design of columns and beam-columns in steel frames. The proposed stiffness reduction approach obviates the need to model member imperfections and to make member buckling checks. While LBA with appropriate stiffness reduction provides inelastic buckling loads of columns, GNA with stiffness reduction is performed for the prediction of beam-column failure. In addition to regular members, the accuracy and practicality of the method is illustrated for irregular members. For the latter case, results indicate that the proposed stiffness reduction method provides more accurate strength predictions in comparison to traditional design approaches. The influence of moment gradient on the development of plasticity (i.e. stiffness reduction) is accounted for by incorporating simple moment gradient factors into the stiffness reduction expressions originally derived for members under uniform bending. The accuracy of the proposed stiffness reduction approach is verified against results obtained through non-linear finite element modelling for all of the considered cases.