High-Strength Concrete in Ultimate Strength Design

The ultimate behavior of concrete structural members was predicted based on the knowledge of the concrete and the steel stress-strain curves and using nonlinear computerized methods. The calculated values of ultimate moment and curvature were compared with some experimental values for beams and columns. The properties of the concrete compression block at ultimate were obtained for normal weight and lightweight concretes of compressive strengths varying from 3,000 psi to 13,000 psi, for beams with varying amounts of tensile and compressive reinforcement and for axially and biaxially loaded columns. The calculated values of the compression block parameters were in general favorable with the ACI recommended values. Some unusual effects of high strength on the value of concrete strain at ultimate and on the ductility of the reinforced sections are noted.