BACKGROUND
Prestressed concrete elements such as beams, girders, piles, and decks are an essential part of the vast majority of bridges built in the United States. Concrete bridge elements that are built with prestressed 7-wire uncoated steel strands are susceptible to corrosion leading to structure deterioration. Delaying strand corrosion will reduce maintenance needs, extend the bridge service life, and enhance the overall safety. Therefore, state departments of transportation (DOTs) have been investigating alternative strand materials such as stainless steel to address steel strand corrosions. However, there is no national standards or specifications to support bridge owners in using stainless steel strands. Bridge owners, fabricators, and contractors need specifications and guidelines for the applications of stainless steel strands for prestressed concrete bridge elements.
OBJECTIVES
The objectives of this research are to (1) propose modification to the AASHTO LRFD bridge design and construction specifications and (2) develop guidelines for the applications of stainless steel strands for prestressed concrete bridge elements including design examples to demonstrate the application of the proposed modifications.
At the minimum, the research shall include pre-tensioning and post-tensioning of concrete bridge elements.
Accomplishment of the project objectives will require at least the following tasks.
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.
PHASE I—Planning
Task 1. Conduct a literature review of relevant research considered to be the state-of-the-practice related to stainless steel strands for prestressed concrete bridge elements. The review shall include published and unpublished research conducted through the NCHRP; FHWA; and other national, international, state, and pooled-fund sponsored research.
Task 2. Synthesize the literature review to identify the knowledge gaps for the applications of stainless steel strands for prestressed concrete bridge elements. In addition, identify the current available stainless steel strands and their applicability to this research from material and mechanical properties perspective. These gaps should be addressed in the proposed modifications or in the recommended future research as budget permits.
Task 3. Propose analytical and testing programs, to be executed in Phases II and III, to achieve the project objectives. At a minimum, the programs should consider the following: (a) member flexure design, (b) mechanical properties of available strands, (c) transfer and development lengths, (d) relaxation losses, (e) stress level, and (f) creep rupture.
Task 4. Identify areas of the current AASHTO LRFD Bridge Design Specifications and AASHTO LRFD Construction Specifications that will be modified in Phase III.
Task 5. Provide an annotated outline of the proposed guidelines for the applications of stainless steel strands for prestressed concrete bridge elements including examples to demonstrate the application of the proposed modifications.
Task 6. Prepare Interim Report No. 1 that documents Tasks 1 through 5 and provides an updated work plan for the remainder of the research. This report must be submitted no later than 4 months after contract execution. The updated work 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 be required to meet in person with the NCHRP project panel to discuss the interim report. Work on Phases II though IV of the project will not begin until authorized by the NCHRP. Phase I shall be limited to $40,000.
PHASE II—Analytical Program
Task 7. Execute the analytical program according to the approved Interim Report No.1.
Task 8. Finalize the testing program work plan. Describe how the testing results will be utilized to achieve the research objectives.
Task 9. Provide a matrix of the examples to demonstrate the application of the proposed modifications.
Task 10. Prepare Interim Report No. 2 that documents the results of Tasks 7 through 9 and provides an updated work plan for the remainder of the project. This report is due no later than 8 months after approval of Phase I. The updated plan must describe the work proposed for Phases III and IV.
Note: Following a 1-month review of Interim Report No. 2 by the NCHRP, the research team will be required to meet in person with the NCHRP project panel to discuss the interim report, if necessary. 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—Testing Program and Specification Modifications
Task 11. Execute the testing program according to the approved Interim Report No.2.
Task 12. Validate the analytical program based on the testing results and update accordingly.
Task 13. Develop the draft proposed AASHTO modifications based on the research results.
Task 14. Prepare Interim Report No. 3 that documents the results of Tasks 11 through 13 no later than 15 months after approval of Phase II. The updated work plan must describe the work proposed for Phase IV.
Note: Following a 1-month review of Interim Report No. 3 by the NCHRP, the research team will be required to meet in person with the NCHRP project panel to discuss the interim report, if necessary. Work on Phase IV of the project will not begin until authorized by the NCHRP. Phase III shall be limited to $350,000.
PHASE IV—Guidelines Development and Final Products
Task 15. Develop the draft guidelines for the applications of stainless steel strands for prestressed concrete bridge elements including examples to demonstrate the application of the proposed modifications based on the research results and proposed AASHTO specifications. The draft guidelines is due no later than 3 months after approval of Phase III.
Task 16. Revise the draft guidelines considering the NCHRP’s review comments. The revised guidelines is due no later than 5 months after approval of Phase III.
Task 17. Prepare final deliverables including: (1) the proposed AASHTO modifications that reflect consideration of the NCHRP’s review comments, (2) guidelines for the applications of stainless steel strands, (3) a final report that documents the entire research effort, and (4) a stand-alone technical memorandum titled “Implementation of Research Findings and Products.” See Special Note D for additional information.
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. Phase IV shall be limited to $60,000.
STATUS: Research in progress
