BACKGROUND

Many of the aging concrete bridges in the United States were designed prior to the nationwide adoption of the American Association of State Highway and Transportation Officials (AASHTO) Load and Resistance Factor Design (LRFD) Bridge Design Specifications (BDS) that were first published in 1994. The current AASHTO LRFD BDS has shear design and detailing provisions that differ from older design standard specifications. Girders of older bridges often do not meet the shear requirements of the current AASHTO LRFD BDS. Moreover, data on concrete members with sizes, cross-sectional shapes, and material grades that reflect actual design and construction practices is lacking. 

The transition toward AASHTO specifications for load and resistance factor rating (LRFR) and the modified compression field theory to determine shear capacity of concrete members has often led to lower bridge ratings than previous evaluation methodologies. Research is needed to help bridge owners overcome the significant lack of data on the shear capacity and behavior of concrete members that are not compliant with the current specifications and to accurately determine the load rating of older concrete bridges.

OBJECTIVE

The objective of this research is to develop procedures for evaluating the shear capacities of in-service prestressed and non-prestressed concrete girders that do not meet current shear design and load rating requirements of AASHTO.

Accomplishment of the project objective will require at least the following tasks.

TASKS

PHASE I—Planning

Task 1.  Conduct a literature review of research and the state of the practice on the analysis and load rating of concrete bridges relevant to this research. The review shall include any existing databases, published and unpublished documentation, past surveys, and research conducted through the NCHRP; the Federal Highway Administration; other national, state, and local agencies; and international organizations.

Task 2.  Synthesize the results of the literature review to identify knowledge gaps related to the research objective. These gaps should be addressed in the final product or the recommended future research, as budget permits.

Task 3. Propose the research plan to be executed in Phase II to achieve the research objective. At a minimum, the research plan shall include:

• A plan to identify and engage key subject-matter experts (e.g., bridge owners, load rating engineers, consulting engineers, etc.) to seek input on the state of the practice and gather relevant data;
• An experimental program to create data and knowledge for large scale prestressed and non-prestressed concrete girders based on the findings of Tasks 1 and 2.  It shall include representative member sizes, cross-sectional shapes, reinforcing and prestressing details, and materials;
• An analytical program that includes an investigation and comparison of measured (experimental) and predicted (analytical) capacities to develop the basis for evaluation procedures;
• An assessment of existing bridge evaluation and design methodologies for shear and develop recommendations of practical method(s) for evaluating shear capacity for girders with noncompliant details;
• An investigation (or consideration) of load application/distribution as it relates to shear; and
• A list of rating examples that covers a range of geometry, materials, and types to demonstrate the use of the proposed procedures. The use of existing bridges is preferred.

Task 4. Prepare Interim Report No. 1 that documents Tasks 1 through 3 and provides an updated work plan for the remainder of the research. The updated plan must describe the process and rationale for the work proposed for Phases II through IV.

PHASE II—Execution

Task 5. Execute the research plan according to the approved Interim Report No. 1.

Task 6. Develop (1) procedures for evaluating shear capacity of prestressed and non-prestressed concrete girders that do not meet current shear design and load rating requirements of AASHTO and (2) recommendations for modifications to the existing requirements for load rating using LRFR as described in Task 3.

Task 7. Prepare Interim Report No. 2 that documents Tasks 5 and 6 and provides an updated work plan for the remainder of the research. The updated work plan must describe the process and rationale for the work proposed for Phases III and IV.

PHASE III—Draft AASHTO Deliverable

Task 8. Revise the proposed procedures after consideration of the panel’s review comments.

Task 9. Develop draft language that may be considered by the AASHTO Committee on Bridges and Structures for inclusion in its next update of the AASHTO Manual for Bridge Evaluation (MBE) for LRFR. The draft language hereafter will be called the AASHTO Deliverable. It should be publication ready (i.e., AASHTO-style format).

Task 10. Prepare load rating examples according to the approved Interim Report No. 2. The examples shall follow the current format and level of details of the AASHTO MBE.

Task 11. Prepare Interim Report No. 3 that documents Tasks 8 through 10 and provides an updated work plan for the remainder of the research. The updated work plan must describe the process and rationale for the work proposed for Phase IV.

PHASE IV—Final Products

Task 12. Revise the AASHTO Deliverable and load rating examples after consideration of the panel’s review comments.

Task 13. Submit the draft final deliverables, including (1) the AASHTO Deliverable, (2) a final report that documents the entire research effort, (3) load rating examples, and (4) a stand-alone technical memorandum titled “Implementation of Research Findings and Products.” 

STATUS: Proposals have been received in response to the RFP. The project panel will meet to select a contractor to perform the work.