This report investigates the use of reinforcing steel, which exhibits no well-defined yield plateau, in the design of structural concrete members through analytical studies. Steel reinforcement considered includes ASTM A1035, A955 (stainless steel), A706, A496, and A82. Analyses considered include material testing and characterization of each steel type for various sizes of reinforcing bar; the calculation of flexural capacities using an elastic-perfectly plastic approach, employing the Ramberg-Osgood function, and through fiber analysis techniques; determining effective tension-controlled and compression-controlled strain limits for high-strength reinforcement; column capacity computations as well as spiral spacing evaluations by considering a refined concrete confinement model; and flexural and shear crack distribution and width through the use of existing equations and computer analysis.
The analytical studies suggest that concrete members designed using high-strength reinforcing bar which lacks a defined yield point will behave similarly to members designed using Gr. 60 steel when the yield strength is defined as 100 ksi. However, idealizing the round-house stress-strain diagram of the high-strength steel as elastic-perfectly plastic does not always provide conservative estimates of flexural capacities.
Strain limits delineating tension-controlled and compression-controlled behavior of structural concrete members can be related to providing a certain amount of ductility in the member at a particular level of strain. Because the stress-strain diagram for A1035 reinforcing steel has no well-defined yield plateau, the currently accepted strain limits of 0.005 and 0.002 were reevaluated. These strain limits have been established to ensure a certain level of ductility for members reinforced with A615 reinforcement. In order to achieve equivalent implied curvature ductilities between A615 and A1035 reinforcement, the strain limits for tension-controlled behavior and compression-controlled behavior of members reinforced with A1035 bars were found to be, respectively, 0.008 and 0.004.
Specification for the spacing limitation longitudinal reinforcement for concrete beams was evaluated. Two possible recommendations were suggested to allow for slightly larger crack widths in members reinforced with A1035 steel.