Recommendations for More Accurate Shear Rating of Prestressed Concrete Girder Bridges

A numerical parametric study was conducted with two primary objectives: (1) to investigate the accuracy of existing AASHTO shear distribution factors for prestressed concrete girder bridges in the United States; and (2) to provide recommendations to more accurately rate bridges for shear and permitting. Results from the parametric study indicated that the longitudinal stiffness (girder composite longitudinal moment of inertia divided by cube of span length) to transverse stiffness (transverse deck strip moment of inertia divided by cube of beam spacing) provided an indication of the elastic shear distribution in nonskewed bridges. Shear distributed more broadly to adjacent girders when the ratio of longitudinal to transverse bending stiffness was lower. The stiffness ratio can be used as a screening tool to delineate cases for which AASHTO shear distribution factors are conservative or unconservative relative to results of detailed finite-element or grillage analyses. Because grillage analyses can account for the distribution of shear associated with truck axle position, they can be used to better determine permit truck demand.