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Iowa State University--Becoming the Best

LRFD Minimum Flexural Reinforcement Requirements


Principal investigators:

Project status

In progress

Start date: 09/30/13
End date: 12/29/17



About the research


According to the American Association of State Highway and Transportation Officials (AASHTO) Load and Resistance Factor Design (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, pre-tensioned, and post-tensioned concrete flexural members (e.g., bonded and unbonded tendons for segmentally and other than segmentally constructed bridges).