Currently, in the AASHTO LRFD Bridge Design Specifications, the nominal flexural resistance of web sections in negative flexure in kinked continuous I-girder bridges, horizontally curved I-girder bridges, and straight I-girder bridges with supports skewed more than 20 degrees from normal is not allowed to exceed the moment at first yield at the strength limit state. As interior-pier sections yield and begin to lose stiffness and shed their load, the forces in the adjacent cross-frames will increase. There is currently no established procedure to predict the resulting increase in the forces without performing a refined nonlinear analysis. In horizontally curved bridges and severely skewed straight bridges with discontinuous cross-frames, significant lateral flange bending effects can occur. The resulting lateral bending moments and stresses are amplified in the bottom compression flange adjacent to the pier as the flange deflects laterally. There is currently no means to accurately predict these amplification effects as the flange is also yielding. Skewed supports also result in twisting of the girders, which is not recognized in plastic-design theory. The relative vertical deflections of the girders create eccentricities that are also not recognized in the theory. Similarly, the nominal flexural resistance of composite sections in positive flexure in kinked continuous I-girder bridges and in horizontally curved I-girder bridges, that would otherwise qualify as compact sections, is currently not allowed to exceed the moment at first yield at the strength limit state. The specifications are currently silent with regard to such sections in straight I-girder bridges with supports skewed more than 20 degrees from normal; as such, the decision whether the section should be treated as a compact or noncompact section is left to the judgment of the engineer. 

The objective of this research is to determine if the restrictions identified in the previous paragraph can be lifted in determining the nominal flexural resistance at the strength limit state of compact web or noncompact web sections in negative flexure, and composite sections in positive flexure that would otherwise qualify as compact sections, in kinked continuous I-girder bridges, horizontally curved I-girder bridges, and straight I-girder bridges with supports skewed more than 20 degrees from normal. The research should identify any deleterious effects on cross-frames forces, flange lateral bending moments and stresses (and the amplification of those moments and stresses as applicable), and torsional displacements of the girders that may need to be considered should these restrictions be lifted. Reasonable and rational design approaches should be developed to calculate the maximum nominal flexural resistance that can be achieved for each type of section (if any adjustments to the current approaches are necessary), along with a means to consider any other related effects that may need to be considered in the design of the various components of the superstructure system. 

The research shall include a parametric study of various practical and realistic I-girder bridge geometries using refined non-linear analyses. It will be limited to sections in negative flexure with compact or noncompact webs and sections in positive flexure that would otherwise qualify as compact sections if the current restrictions on bridge geometry were not in effect.