Efficient application of the Reduced Stress Method for built-up I sections

Abstract

Reduced Stress Method is an alternative to the effective width method of EN 1993-1-1. Because of its built-in conservatism it is less used in practice for the design of building structures. The proposed new application reduces this conservatism. The final stress distribution is obtained with a 2-step iteration which automatically handles the effect of the displacement of the center of gravity of the original gross cross-section. Instead of calculating effective widths or reducing the whole cross-section resistance, reduced thicknesses are assigned to the proper individual plates. Reduction is obtained using the standard plate buckling curves where the plate slenderness is calculated with the help of linear buckling analysis. The buckling shape relevant to each plates of the cross-section is selected with a deformation energy-based buckling sensitivity analysis. The proposed method is demonstrated on a series of welded I beam-column Class 4 sections subjected to constant axial compression force and strong axis bending moment. Resistances are compared with results obtained by the EN 1993-1-3 effective width method and by numerical simulation. The method is ready to be built into computer software which can handle shell finite elements and perform linear buckling analysis.