A new model for calculating the ultimate shear resistance of steel I-section girders

The design resistance in shear of thin-walled I-sections has elicited numerous theories over the past decades. While there is a consensus on the post-buckling tension-field action that increases the ultimate resistance of thin webs in shear, the mechanism governing this tension-field action still remains debated. Presently, four constituent components for the shear resistance of I-sections are identified: (1) the resistance of the isolated web subject to a pure shear stress; (2) an increase in the web buckling stress due to flexural restraints provided by the flanges; (3) an increased web post-buckling resistance due to membrane restraint provided by the flanges; and (4) a direct contribution from the flanges to the shear resistance of the I-section. Each of these components is examined through parametric studies using finite element (FE) models analysed within Abaqus that are validated against published experimental results. A new design methodology for the resistance of I-sections in shear is presented, with closed-form expressions developed for each of the four component contributions. When compared with the current approach within EN 1993-1-5, the proposed formulae predict the shear resistance of the cross-section with greater accuracy and consistency.