Shear strength and moment-shear interaction in transversely stiffened steel I-girders

With the advent of HPS495W steel, hybrid I-girders have again become advantageous in bridge design. Unfortunately, the use of tension field action is not permitted in determining the shear resistance of hybrid girders in prior AISC and AASHTO specifications. This is a significant penalty on the strength of these member types. Also, the checking of moment-shear (M-V) strength interaction is a significant complicating factor in the design and capacity rating of I-girders that use tension field action. The requirements for the shear strength design and the equations for M-V strength interaction in the 1999 AISC and 1998 AASHTO specifications were developed originally without the benefit of a large body of experimental tests and refined finite-element simulations. This paper presents the results from the collection and analysis of data from a total of 186 high-shear low-moment, high-shear high-moment, and high-moment high-shear experimental I-girder tests. References to corroborating refined finite element studies are provided. Particular emphasis is placed on the extent to which web shear postbuckling (tension-field) strength is developed in hybrid I-girders, as well as on the interaction between the flexural and shear resistances in hybrid and nonhybrid I-section members. The results of the study indicate that, within certain constraints that address the influence of small flange size, Basler's shear resistance model can be used with the flexural resistance provisions of the 2004 AASHTO and 2005 AISC specifications without the need for consideration of M-V strength interaction. Also, the research shows that a form of the Cardiff model can be used with these flexural resistance provisions without the need to consider M-V strength interaction. These conclusions apply to both nonhybrid and hybrid I-girder designs.