LRFD Minimum Flexural Reinforcement Requirements

According to the AASHTO LRFD Bridge Design Specifications, minimum reinforcement provisions are intended to reduce the probability of brittle failure by providing flexural capacity greater than the cracking moment. There is a concern with the current AASHTO LRFD minimum flexural reinforcement requirements when it’s applied to pretensioned or post-tensioned concrete flexural members. Increasing the nominal capacity of a member can result in increasing the cracking moment of the same member. This makes the design process iterative, and the current minimum reinforcement requirement for post-tensioned members is difficult to satisfy. This also may lead to less efficient design of pretensioned/post-tensioned concrete flexural members. Provisions for the design of minimum flexural reinforcement must be suitable for all structure and reinforcement types covered by the AASHTO LRFD Bridge Design Specifications and should be consistent with the LRFD design philosophy.  The objective of this research is to propose revisions to the AASHTO LRFD Bridge Design Specifications minimum flexural reinforcement provisions. The research should consider reinforced, pretensioned, and post-tensioned concrete flexural members (e.g., bonded and unbonded tendons for segmentally and other than segmentally constructed bridges). Accomplishment of the project objective will require at least the following tasks. (PHASE I—Planning): (1) Conduct a critical review of relevant specifications, technical literature, and owner and industry experiences. The review should cover research findings from both domestic and foreign sources. (2) Propose analytical and testing programs to investigate minimum flexural reinforcement. The proposed analytical program should consider available test data in addition to the testing program to be performed under Phase III. The testing program should cover the design of laboratory specimens to be tested in Phase III. The design should consider the scale effect and testing configurations on the accuracy of the results. (3) Prepare Interim Report No. 1 that documents Tasks 1 and 2 and provides an updated work plan for the remainder of the project. This report is due no later than 3 months after the contract award. The updated plan must describe the process and rationale for the work proposed for Phases II through V. (PHASE II—Analytical Program and Testing Program Development): (4) Execute the approved work plan for the analytical program.  (5) Identify existing articles of the AASHTO LRFD Bridge Design Specifications that require modification. (6) Finalize the testing program development to validate the findings of the analytical program. (7) Prepare Interim Report No. 2 that documents Tasks 4 through 6 and provides an updated work plan for the remainder of the project. This report is due no later than 9 months after approval of Phase I. The updated plan must describe the work proposed for Phases III through V. (PHASE III—Testing Program and Analytical Program Validation) (8) Execute the testing program according to the approved work plan. (9) Validate and finalize the analytical program based on test results. (10) Prepare Interim Report No. 3 that documents Tasks 8 and 9 of Phase III no later than 12 months after approval of Phase II. (PHASE IV— Proposed Modifications to AASHTO LRFD Bridge Design Specifications): (11) Based on the analytical and testing investigations, develop specification and commentary language for proposed changes to the AASHTO LRFD Bridge Design Specifications supported with design examples for different bridge design types (e.g., bonded and unbonded tendons for segmentally and other than segmentally constructed bridges). (12) Quantify the potential economic impact of the proposed revisions. (13) Prepare Interim Report No. 4 that documents Tasks 11 and 12 of Phase IV no later than 6 months after approval of Phase III. (PHASE V—Final Products): (14) Update proposed modifications to the AASHTO LRFD Bridge Design Specifications after consideration of Interim Review No. 4 comments and prepare ballot items for AASHTO Highway Subcommittee on Bridges and Structures consideration. (15) Prepare a final report that documents the entire research effort. 

Language

  • English

Project

  • Status: Active
  • Funding: $550000
  • Contract Numbers:

    Project 12-94

  • Sponsor Organizations:

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590

    American Association of State Highway & Transportation Officials (AASHTO)

    444 North Capitol Street, NW, Suite 225
    Washington, DC  United States  20001

    National Cooperative Highway Research Program

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC  United States  20001
  • Project Managers:

    Dekelbab, Waseem

  • Performing Organizations:

    Iowa State University, Ames

    Ames, IA  United States  50011
  • Principal Investigators:

    Sritharan, Sri

  • Start Date: 20130930
  • Expected Completion Date: 20180731
  • Actual Completion Date: 20161229
  • Source Data: RiP Project 38351

Subject/Index Terms

Filing Info

  • Accession Number: 01547641
  • Record Type: Research project
  • Source Agency: Transportation Research Board
  • Contract Numbers: Project 12-94
  • Files: TRB, RiP
  • Created Date: Dec 12 2014 1:00AM