Bridges constructed with adjacent precast prestressed concrete box beams have been in service for many years and provide an economical solution for short and medium span bridges. A recurring problem is cracking in the longitudinal grouted joints between adjacent beams, resulting in reflective cracks forming in the asphalt wearing surface or concrete deck. The cracking appears to be initiated by, but not limited, to stresses caused by temperature gradients, live loads, transverse post-tensioning, or grout shrinkage. Once the cracking has occurred, chloride-laden water can penetrate the cracks and cause corrosion of the reinforcement and prestressing strand.
NCHRP Synthesis 393: Adjacent Precast Concrete Box Beam Bridges: Connection Details reported a wide variety of practices used by state highway agencies for the connection details between adjacent box beams. These practices include partial depth or full depth grouted keyways, keyways grouted before or after transverse post-tensioning, prepackaged or non-prepackaged grout materials, post-tensioned or non-tensioned transverse ties, a wide range of applied transverse post-tensioning forces, and cast-in-place concrete decks or no decks. A few states reported that their practices had reduced the longitudinal cracking, whereas others had not been successful using similar practices.
In 2014, FHWA conducted extensive evaluation of the use of the ultra-high performance concrete (UHPC) connections for adjacent box beam bridges to address the connection performance. In fact, the FHWA-developed UHPC connections have been used by some states.
Since the previous research focused on the connections’ performance as an individual component, there is a need to evaluate their performance as part of an overall adjacent precast box beam bridge system. In addition, new adjacent precast box beam bridge systems could be developed by integrating both proven and innovative connections.
The objectives of this research are to (1) develop guidelines for the design and construction of various adjacent precast box beam bridge systems to enhance performance of connections and bridge service life and (2) propose design and construction specifications with commentary in the format of the AASHTO LRFD Bridge Design 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 critical review of relevant NCHRP reports and specifically NCHRP Project 12-95 (see Special Note A). In addition, the review should include owner and industry practices, FHWA-related research, and other research findings from both foreign and domestic sources.
Task 2. Summarize the performance of the various connections identified in Task 1 and prepare a list of adjacent precast box beam bridge systems to be evaluated under Phases II and III. At a minimum, the research shall include: conventional grouts/concrete for full and partial-depth reinforced connections with and without structural deck, keyway surface preparation, and, if needed, transverse post-tension.
Task 3. Propose performance criteria for evaluating (1) the performance of conventional and UHPC connections and (2) the global structural performance of bridge systems.
Task 4. Propose an analytical evaluation program for the proposed systems to be executed in Phase II. The UHPC connections shall not be included in the analytical and testing programs as they have been tested by FHWA.
Task 5. Propose a system test program to be executed in Phase III. The plan for the system tests should be presented in a matrix format. At a minimum, two system tests shall be conducted.
Task 6. Propose areas of the AASHTO bridge design and construction specifications that will require modification or addition.
Task 7. Prepare Interim Report No. 1 that documents Tasks 1 through 6 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 V. This report must be submitted no later than 4 months after contract award.
PHASE II—Analytical Program
Task 8. Execute the analytical program according to the approved Interim Report No.1.
Task 9. Finalize the system test program work plan and describe how the test results will be utilized to develop the guidelines.
Task 10. Prepare Interim Report No. 2 that documents Tasks 8 and 9 and provides an updated work plan for Phases III through V. This report must be submitted no later than 9 months after approval of Phase I.
PHASE III—System Test Program
Task 11. Execute the system tests program according to the approved Interim Report No. 2. Validate the analytical program based on the results of the system test program.
Task 12. Prepare an annotated table of contents for the draft guidelines and propose design examples to demonstrate the application of proposed guidelines and specifications.
Task 13. Prepare Interim Report No. 3 that documents Tasks 11 and 12 and provides an updated work plan for the remainder of the project. This report must be submitted no later than 12 months after Phase II approval.
PHASE IV—Guidelines and Specifications Development
Task 14. Develop the draft guidelines, modifications to the AASHTO design and construction specifications, and design examples and connection details to demonstrate the application of the proposed guidelines. Prepare AASHTO agenda items for the AASHTO Highway Committee on Bridges and Structures.
Task 15. Prepare Interim Report No. 4 that documents this phase. This report must be submitted no later than 4 months after approval of Phase III.
PHASE V—Final Products
Task 16. Revise the draft guidelines, modifications to AASHTO bridge design and construction specifications, design examples and connection details after consideration of the panel’s review comments.
Task 17. Prepare final deliverables including: (1) the revised deliverables of Task 15, (2) a final report that documents the entire research effort, and (3) a stand-alone technical memorandum titled “Implementation of Research Findings and Products.” See Special Note E for additional information.
STATUS: Research in progress.