Yield Interaction Equations for Nominal Bending Strength of Curved I-Girders

Abstract

Horizontally curved I-girders are subjected to combined vertical bending and torsion under gravity loading alone. The torsional behavior of open I-shaped girders is commonly and conveniently equated to self-equilibrating lateral bending moments in the flanges. The interaction of vertical bending and this lateral flange bending effectively reduces the vertical moment carrying capacity of the section. Yield interaction equations for predicting the nominal bending strength of horizontally curved steel I-girders subjected to vertical moment and torsion are derived. Singly symmetric composite and noncomposite I-shaped cross sections in both the positive and negative moment zones are considered. Strength criteria considered are: (1) complete plastification of the cross section for compact sections; (2) partial yield penetration for compact-flange sections; and (3) initial yielding at the extreme flange tip for noncompact sections. A total of 17 interaction cases are ultimately considered. These strength criteria are based purely on the static equilibrium of the cross section with no secondary amplification considered. The limitations and applicability of the derived equations toward design use are demonstrated and analyzed.