Finite Element Analysis of Splayed Steel Girder Bridges

Abstract

A splayed girder bridge is a bridge which consists of a deck slab supported on girders with linearly varying spacing. The simple formulas and approximate design procedures in the AASHTO LRFD Bridge Design Specifications are supposed to be used with regular bridges, where the girders are parallel and the deck slab width is constant. For splayed girder bridges, the specifications suggest a refined method of analysis, which could be expensive and time-consuming. Extending the simple live load girder distribution factors and the deck slab strip method to splayed girder bridges would be very helpful for bridge designers. The objective of this research is to investigate the effect of girder splayedness in slab-on-steel-girder bridges on the dead and live load distribution in the deck slab as well as among the interior and exterior girders. Fifteen composite steel girder bridges are analyzed by the finite element method using the computer software ANSYS. In the computer model, 4-node rectangular shell elements were used for the steel girder flanges and web, 2-node beam elements for the cross-bracing, and 8-node solid elements in the deck slab. Linearly-elastic material behavior is utilized and the model is verified against laboratory and field tests of actual bridges. The effects of the girder splayedness angle, girder spacing, number of girders, deck slab thickness, span length, girder stiffness, and presence of cross-bracing are considered. The study showed that the tributary width concept is reliable for determining the dead load on the splayed girders. Also, the girder distribution factors for flexure in the AASHTO LRFD specifications can be reasonably used for splayed girder bridges if the specific girder spacing at the location of each axle of the truck in the longitudinal direction is considered. On the other hand, the lever rule can provide a good estimate of the live load distribution among splayed girders when subjected to shear. With regard to the live and dead load effect in the deck slab, the equivalent strip method can be a reasonable predictor of the critical positive and negative bending moments in the slab interior regions and in the overhang, provided more than one strip are taken at some discrete locations along the bridge centerline.