The current AASHTO specification requirements for the web bend-buckling strength-reduction factor (Rb) do not consider the influence of longitudinal stiffeners on the flexural resistance of steel I-girders subsequent to the theoretical bend-buckling of a slender web. This is a deficiency that can have significant impact, especially in regions of continuous-span girders subjected to negative moment. This paper evaluates the contribution of single-web longitudinal stiffeners to the yield limit state flexural resistance of slender-web steel I-girders, often referred to as the plateau resistance for the lateral torsional and flange local buckling limit states. Based on test simulation studies, the authors recommend a cross-section model that captures the response of the postbuckled web for both homogeneous and hybrid girders subjected to uniform moment. The proposed model offers up to 60% improvement relative to the current AASHTO specifications. © 2016 American Society of Civil Engineers.