Of more than 600,000 bridges listed in the Federal Highway Administration's (FHWA) National Bridge Inventory, close to 1,000 are movable highway bridges. The design and installation of structural, mechanical and electrical systems provide significant challenges for designers, contractors and owners in any movable highway bridge project. The primary design specifications for movable bridge design and construction is the AASHTO LRFD Movable Highway Bridge Design Specifications published in 2000 with 2002 interim revisions. The second edition of the specifications was published in 2007, and the most recent interim revisions were in 2015. Based on the input from movable highway bridge owners, designers and industry representatives, there is an immediate need to incorporate reliability-based design methodology and to reflect advances in electrical, mechanical, and traffic/marine safety systems into the current specifications.
The objectives of this research are to (1) develop a reliability-based methodology to design electrical, mechanical, and traffic/marine safety elements and systems for movable highway bridges and (2) propose revisions to the AASHTO LRFD Movable Highway Bridge Design Specifications including all sections.
Accomplishment of the project objectives will require at least the following tasks.
Task 1. Conduct a literature review of relevant domestic and international practice and research findings related to electrical and mechanical systems used in movable highway bridges including NCHRP Project 20-07/Task 348, “Review of the AASHTO LRFD Movable Bridge Design Specifications for Future Updates”. Other disciplines where reliability-based approaches are being integrated into engineering design should be explored and documented.
Task 2. Define and discuss the application of a reliability-based approach to the design of electrical and mechanical elements and systems. Discuss the quantity and quality of data required for the application of reliability theory and practical limitations.
Task 3. Propose a reliability-based methodology to be developed in Phase II. At a minimum, the methodology shall address the following:
a. Acceptable level of reliability for electrical and mechanical elements and systems;
b. Limit states to design of electrical and mechanical elements and systems where applicable; and
c. Reliability of individual component and system.
Task 4. Identify areas of the existing specifications that required modification or update with consideration to the latest developments in movable bridge design and rehabilitation. Provide a detailed outline of the proposed changes and reorganization of the existing specifications.
Task 5. Prepare Interim Report No. 1 that documents Tasks 1 through 4 and provides an updated work plan for the remainder of the project. This report must be submitted no later than 5 months after contract award.
PHASE II—Reliability-Based Methodology Development
Task 6. Develop the reliability-based methodology according to the approved Interim Report No.1.
Task 7. Develop detailed illustrative examples to demonstrate the full range of applicability of the proposed methodology.
Task 8. Complete a sample section of the AASHTO movable design specifications to be selected by NCHRP. This section should be publication-ready (i.e., AASHTO-style) format with appropriate level of detail.
Task 9. Prepare Interim Report No. 2 that documents Tasks 6 through 8 and provides an updated work plan for the remainder of the project. This report must be submitted no later than 18 months after approval of Phase I.
PHASE III—Specification Revision and Update
Task 10. Revise and update remaining sections of the specifications and develop design examples demonstrating the proposed revisions. The recommended AASHTO specifications shall be provided in AASHTO-style format.
Task 11. Prepare Interim Report No. 3 that documents Task 10 and provides an updated work plan for the remainder of the project. This report must be submitted no later than 6 months after Phase II approval.
PHASE IV—Final Products
Task 12. Revise the AASHTO specifications and design examples after consideration of the panel’s review comments and prepare a ballot item for the AASHTO Highway Subcommittee on Bridges and Structures.
Task 13. Prepare final deliverables including: (a) a final report that documents the entire research effort and (b) the proposed draft AASHTO specifications and design examples.
STATUS: Research in progress.