In the recently completed U.S. Department of Transportation (USDOT) Study, Review of U.S. Department of Transportation Truck Size and Weight Study (USDOT TS&W Study), a small number of bridges in relation to the total population of bridges were evaluated for force effects and the associated cost to strengthen or replace them due to the increased weight of the new legal truck configurations and gross weights. A broader study of the force effects, such as increased demand on girders and deck, reduction in service life, and remaining fatigue life, on the total population of bridges in the United States would be beneficial to understand and predict more accurate cost effects of increasing legal loads. More generally, the Highway Subcommittee on Bridges and Structures needs a roadmap that acknowledges ongoing and complete truck-size-weight-cost studies related to bridge condition and provides the logical next steps.

At the minimum, the parametric study should compare the force effects (moments and shears) of standard AASHTO bridge design trucks (HS-20, HS-15, H-20, H-15 and HL-93) over a full range of span lengths (20’ to 250’) for both simply supported and continuous structures to the six trucks evaluated in the USDOT TS&W study.

The objectives of this research were to (1) conduct a parametric study to assess the impact of increasing legal loads on highway bridges, including local and currently posted bridges, on the cost of bridge replacement per state; (2) prepare a roadmap of study items and actions necessary to make the true cost effects of increasing legal loads known by decision makers.

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