Influence of Girder Flaring on Load Effect in Girders of Composite Steel Bridges

A flared or splayed girder bridge is a structure made up of a concrete slab on girders with linearly varying spacing along the length. For such an irregular bridge, the girder distribution factors in the AASHTO LRFD Bridge Design Specifications are not applicable. In lieu of using a refined method of analysis, the study at hand proposes a simple approach for computing the dead and live load effect in the girders. To do so, fifteen composite steel girder bridges are analyzed by the finite element method to determine the influence of the girder flaring angle, girder spacing, number of girders, deck slab thickness, span length, girder stiffness, and presence of cross-bracing on the load distribution within the bridge. This study showed that the tributary width concept is a reliable approach for determining the dead load effect on the splayed girders, especially for the case of shored construction. The girder distribution factors for flexure in the AASHTO specifications can be reasonably utilized for such irregular bridges if the girder spacing at the location of each truck axle is considered, leading to a maximum of 14% difference on the conservative side between the AASHTO approach and the finite element analysis. On the other hand, the lever rule can provide a good estimate of the live load distribution among the splayed girders when subjected to shear, as the maximum safe deviation from the finite element outcome in this situation is less than 10%.