The National Academies

NCHRP 20-07/Task 217 [Completed]

Verification and Implementation of Strut-and-Tie Model in LRFD Bridge Design Specifications
[ NCHRP 20-07 (Research for AASHTO Standing Committee on Highways) ]

  Project Data
Funds: $74,986
Research Agency: Modjeski & Masters
Principal Investigator: Barney Martin
Effective Date: 4/28/2006
Completion Date: 10/27/2007
Comments: Completed

The first edition of the AASHTO LRFD Bridge Design Specifications, published in 1994, introduced the Strut-and-Tie Model (STM) for design and detailing of concrete members. The model applies at geometric and load discontinuities, which are encountered in all components of concrete bridges. Ten years after publication of the first edition of the LRFD Specifications, there is still a lot of confusion, and lack of comfort, regarding how to apply the STM provisions to new designs. Design engineers are finding it equally difficult to use the STM to evaluate existing structures. Starting in October 2007, all new bridges receiving federal aid must be designed by the AASHTO LRFD Bridge Design Specifications.

The objectives of this project were (1) to critically review and expand existing Strut-and-Tie Model provisions of the AASHTO LRFD Bridge Design Specifications, and (2) to develop design examples to help implement the STM provisions for design of new structures and for evaluation of existing structures.

The project is complete.     The report contains recommended revisions to the AASHTO LRFD Bridge Design Specifications and 10 detailed design examples.  The report can be downloaded 

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