Design of web-tapered steel I-section members by second-order inelastic analysis with strain limits

A consistent design approach, performed by second-order inelastic analysis using beam finite elements with strain limits, is proposed for web-tapered steel members. In the proposed design approach, a geometrically and materially nonlinear analysis with imperfections (GMNIA) of the tapered steel member is carried out and the ultimate strength of the member is signified by reaching either the strain limit defined according to the Continuous Strength Method (CSM) or the peak load factor, whichever occurs first. To consider the beneficial effect of strain gradients along the lengths of the members on local cross-section resistances, the strains are averaged over the local buckling half-wavelength. The accuracy of the proposed design approach is verified against results from nonlinear shell finite element modelling as well as a number of experiments on tapered members considering various taper ratios, loading conditions and member slenderness values. The proposed method provides more accurate and consistent ultimate strength predictions than EN 1993-1-1 [1], because the following aspects, which are ignored in traditional design methods, are captured: (1) the interaction between cross-section elements for the consideration of local buckling, (2) the influence of local moment gradients on cross-section resistance, (3) the partial plastification of cross-sections and (4) strain hardening.