A segmental bridge is constructed in short sections or segments that are either precast or cast-in-place concrete. Segmental bridges were first built in the United States in the 1970s and have proven to be an efficient design for long span bridges. The earliest segmental bridges were designed, constructed, and load rated using methods that were not codified by the American Association of State Highway and Transportation Officials (AASHTO), and differ significantly from the current AASHTO load and resistance factor design (LRFD), load factor rating (LFR), and load and resistance factor rating (LRFR) methodologies. As a result, the use of current AASHTO LFR and LRFR methodologies to load rate existing segmental bridges has resulted in a significant capacity reduction in comparison to the old load rating procedures. In addition, there are limited resources for owners and consultants to accurately load rate segmental bridges due to the complexities. There is a need to develop load rating guideline to accurately determine the load rating capacity of segmental bridges to ensure safety and mobility.
The objectives of this research are to (1) develop a proposed AASHTO guideline for load rating of segmental bridges; (2) propose revisions for the AASHTO Manual for Bridge Evaluation (including LFR and LRFR) and any necessary related revisions to the AASHTO LRFD Bridge Design Specifications; and (3) develop detailed rating examples with supporting training materials to demonstrate the proposed guideline and revisions to AASHTO specifications.
Accomplishment of the project objectives will require at least the following tasks.
Task descriptions are intended to provide a framework for conducting the research. The NCHRP is seeking the insights of proposers on how best to achieve the research objectives. Proposers are expected to describe research plans that can realistically be accomplished within the constraints of available funds and contract time. Proposals must present the proposers' current thinking in sufficient detail to demonstrate their understanding of the issues and the soundness of their approach to meeting the research objectives.
Task 1. Conduct a literature review of relevant domestic and international research and guidelines including the historical development of load rating specifications. The domestic review should include research conducted through the NCHRP; Strategic Highway Research Program 2 (SHRP2); FHWA; and other national, state, and pooled-fund sponsored research. The review should cover research findings, existing guidelines, and owner and industry experience.
Task 2. Synthesize the literature review to identify the knowledge gaps and the data required for load rating of segmental bridges. These gaps should be addressed in the final product or in the recommended future research, as budget permits.
Task 3. Propose an analytical program to investigate the load rating of segmental bridges and achieve the research objectives to be executed in Phase II. At a minimum, the research should address the following:
1. capacity of segmental bridges including those designed prior to the AASHTO specifications considering the following:
a. longitudinal and transverse capacities,
b. strength across different types of joints,
c. principal tensile stress, and shear and torsional effects,
d. creep, shrinkage, thermal, and other load effects, and
e. system factors.
2. the data required including current bridge condition (including inspection reports, field surveys and measurement, and deflection), design and as-built plans, construction documents (contractor proposed changes, shop drawings, casting and erection plans, material properties, casting records, construction loads, etc.), maintenance records (including repair and rehabilitation records);
3. inventory and operating rating (i.e., design, legal, emergency vehicle, and permit load rating); and
4. reliability assessment of service and strength limit states.
Task 4. Prepare a detailed outline of the proposed AASHTO guideline and identify any required revisions to the AASHTO Manual for Bridge Evaluation and AASHTO LRFD Bridge Design Specifications. Propose at least four load rating examples to demonstrate the proposed guideline.
Task 5. Prepare Interim Report No. 1 that documents Tasks 1 through 4 as well as the data archiving plan (see Special Note C) and provides an updated work plan for the remainder of the research no later than 4 months after contract award. The updated plan must describe the process and rationale for the work proposed for Phases II though IV.
Note: Following a 1-month review of Interim Report No. 1 by the NCHRP, the research team will meet with the project panel to discuss the interim report. Work on Phases II through IV of the project will not begin until authorized by the NCHRP. Phase I shall be limited to $30,000.
PHASE II—Analytical Program
Task 6. Execute the analytical program according to the approved Interim Report No.1.
Task 7. Complete a sample section of the guideline to be selected by NCHRP. This section should be publication ready (i.e., AASHTO-style format) with appropriate level of details.
Task 8. Prepare Interim Report No. 2 that documents Tasks 6 and 7 and provides an updated work plan for Phases III and IV no later than 9 months after approval of Phase I.
Note: Following a 1-month review of Interim Report No. 2 by the NCHRP, the research team will meet with the project panel to discuss the interim report. Work on Phases III and IV of the project will not begin until authorized by the NCHRP. Phase II shall be limited to $150,000.
PHASE III— Proposed Provisions to the AASHTO Specifications
Task 9. Develop the remaining sections of guideline and prepare illustrations (e.g., flowcharts, graphs). Prepare proposed revisions to the AASHTO Manual for Bridge Evaluation and AASHTO LRFD Bridge Design Specifications. The recommended guideline shall be provided in AASHTO-style format.
Task 10. Develop the load rating examples and the supporting training materials.
Task 11. Prepare Interim Report No. 3 that documents Tasks 9 and 10 of Phase III no later than 9 months after approval of Phase II.
Note: Following a 1-month review of Interim Report No. 3 by the NCHRP, the research team will meet with the project panel to discuss the interim report. Work on Phases IV of the project will not begin until authorized by the NCHRP.
PHASE IV—Final Products
Task 12. Revise the guideline and proposed provisions of the AASHTO specifications after consideration of review comments and prepare ballot items for AASHTO Highway Subcommittee on Bridges and Structures consideration.
Task 13. Prepare final deliverables including: (1) a final report that documents the entire research effort; (2) the proposed AASHTO guideline; (3) the proposed provisions to the AASHTO specifications; (4) the load rating examples with training materials; and (5) a stand-alone technical memorandum titled “Implementation of Research Findings and Products.” See Special Note E for additional information. The draft deliverables are due no later than 2 months after approval of Phase III.
Note: Following receipt of the draft final report, the remaining 3 months shall be for NCHRP review and comment and for research agency preparation of the revised final report. Phases III and IV shall be limited to $120,000.
STATUS: Research in progress