A simplified method for bridge rating and design using the federal gross weight formula

The purpose of this study is to show that the federal gross weight can be used as a tool to evaluate the structural response of bridges for both bridge rating and design. To date, the federal gross weight formula is used by state departments of transportation to regulate overload vehicles that use state bridges. In this study, a simple technique for computing the maximum bending moment in a multiple span continuous bridge is presented. This maximum bending moment is calculated using information such as the vehicle's wheelbase length, bridge span length, and the federal gross weight. Actual overload permit vehicle configurations, provided by the Tennessee Department of Transportation, were used in the study. The bending moments obtained from the BRASS program, using actual permit configurations, were used to compare with bending moments computed based on the federal gross weight concentrated load. BRASS is a structural software program used to calculate actual live load moments. Based on 728 bridge-overload vehicle combinations, it was found that the technique presented yielded a reasonable estimate for the maximum bending moment.