Recommended LFRD Minimum Flextural Reinforcement Requirements


ABSTRACT

This report documents and presents the results of a study of minimum reinforcement requirements for the design of concrete bridge structures. This study included a review of U.S. and international practice, test data and research findings related to minimum reinforcement requirements and flexural cracking of concrete structures. A total of 4 representative methods of specifying minimum reinforcement were evaluated and compared by performing design calculations on a wide range of concrete bridge members. The findings of this study suggest that in nearly all cases lightly reinforced concrete members can develop the nominal flexural strength and have significant strength and ductility reserves after cracking has occurred. Also, the modulus of rupture over estimates the flexural cracking stress of concrete bridge members. A rational approach to the specification of minimum reinforcement is proposed, where variables are appropriately factored and includes the maximum rather than nominal strength of the section as a true measure of ductile versus brittle response.






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