Minimum reinforcement in flexural concrete member

In lightly reinforced concrete members, the area of steel (As) cannot be less than a minimum value (As,min), so that the ultimate limit state can be reached under a yielding moment higher than the cracking moment of the plain concrete. Also in the service stage, a minimum amount of reinforcement should be provided in tensile zones in order to reduce crack widths. Minimum reinforcement is provided in concrete beams in order to improve their behavior towards cracking and ductility at failure. Generally, the codes of practice for minimum steel ratios, longitudinal and transversal, are mainly empirical and do not include all the influential parameters in them. Therefore, due to the fact that they lack a theoretical background, different codes can give values for the minimum reinforcement ratios that greatly differ from each other. Also the validity of these equations may be questioned in the case of high strength concrete and prestressed concrete beams.

For this thesis, the following have been used to establish a theoretical background for minimum longitudinal reinforcement in beams: (1) ACI 318 codes (From 1963 to the Current 2008 Version); (2) LRFD AASHTO specifications (4th Edition 2007); (3) Textbook of Wang and Salmon (2005, 7th Edition); (4) ACI Paper journals; (5) Non U.S codes (Canada, Australia, and New Zealand).

Included in this thesis is an approach used to calculate the minimum reinforcement ratio that is required for the ductile behavior at failure of prestreesed and nonprestressed concrete beams. Comparisons are also made between the ACI codes, the LRFD AASHTO code, and between the ACI codes and some non U.S codes such as the codes from Canada, Australia and New Zealand.