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.
The objectives of this research are 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.
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.
Task 1. Develop a methodology to determine comparative force effects for the AASHTO design trucks and the six trucks used in the USDOT TS&W Study. The Methodology should consider querying the National Bridge Inventory state-by-state for the bridges that have the comparative operating ratings that are exceeded by the six trucks in the USDOT TS&W Study.
Task 2. Determine the replacement costs for each state for each of the six scenario trucks using the average cost of bridge replacement per square foot for each state and summarize the cost impact for the nation for each of the six truck scenarios.
Note: Submit a draft letter report for Tasks 1 and 2 no later than 5 months after contract award. NCHRP approval will be required before proceeding with the remaining tasks.
Task 3. Prepare a roadmap of study items and actions necessary to make the true cost effects of increasing legal loads known by decision makers. The roadmap shall include prioritized list of needed research to investigate the questions and issues that would result from increasing legal loads.
Task 4. Present the research findings to the AASHTO Subcommittee on Bridges and Structures, Technical Committees: T-5 Loads and Load Distribution and T-18 Bridge Management, Evaluation, and Rehabilitation.
Task 5. Submit a final report describing the entire research. Following receipt of the draft final report, the remaining 2 months shall be for NCHRP review and comment and for research agency preparation of the revised final report.
STATUS: Research in progress.