Existing Bridge Formulas for Truck-Weight Regulation from International Jurisdictions and Resulting Load Stresses on Single-Span Bridges

Abstract

This paper identifies and characterizes existing bridge formulas from international regions and presents the results of an analysis of the allowable gross vehicle weights and bridge load stress effects on single-span bridges resulting from these formulas. This is done to provide insight into this method of regulating truck size and weight to identify influencing factors and considerations for future decisions regarding the creation of new bridge formulas, or modification of existing ones. It is found that bridge formulas vary significantly in terms of the level of restrictiveness of allowable loads and imposed load effects due to the design criteria used in their development including truck configurations, bridge design methods, design loads, and allowable load rating. Bridge formulas should be designed to limit the imposed stresses on bridges based on criteria suitable to a jurisdiction’s truck fleet and infrastructure characteristics in order to adequately regulate truck sizes and weights. Many issues may result from the implementation of an unsuitable bridge formula for the infrastructure and transportation characteristics of a jurisdiction in terms of the design overstress criteria and additional axle spacing and weight limits. The unintended, and possibly undesirable, outcomes of implementation of a bridge formula must be monitored and resolved for safety, dynamic performance, and infrastructure impacts. With the continuously changing infrastructure and truck transportation characteristics, bridge formulas must be reevaluated and updated to ensure the adequacy of limit weights.