Simplified Load Distribution for Vehicles with Nonstandard Axle Gauges

Several simplified methods have been developed to determine the live-load distribution factors for overweight vehicles on slab-on-girder bridges; however, these methods were developed for vehicles with standard axles. Many vehicles exist with nonstandard axle configurations, such as two-wheel axles that are wider than 6 ft (1.83 m) and four-wheel axles with wheels that are evenly or unevenly spaced. For these vehicles, a rigorous analysis is generally desired but is often deemed uneconomical. Therefore, a simplified method should be an asset to the bridge community and the trucking industry. A simplified method for determining live-load distribution factors for vehicles with nonstandard axle configurations is presented. Distribution factor formulas for moment and shear in interior and exterior girders are given. These formulas account for the transverse axle configurations that compose a vehicle. Several two- and four-wheel axle configurations are considered. The distribution factor formulas for slab-on-girder bridges presented in the AASHTO LRFD Bridge Design Specifications are incorporated into the proposed simplified method. The simplified method formulas were developed to approximate the results from a rigorous finite strip method. Comparisons are presented as verification of the accuracy of the simplified method. The simplified method results are usually conservative and correlate reasonably well with the rigorous results. In general, simplified methods worked better for interior girders than for exterior girders, and moment was better predicted than shear.