OBSERVED STRESS-STRAIN BEHAVIOR OF CONFINED CONCRETE
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Thirty-one nearly full-size reinforced concrete columns, of circular, square, or rectangular wall cross section, and containing various arrangements of reinforcement, were loaded concentrically with axial compressive strain rates of up to 0.0167/s. The circular sections contained longitudinal and spiral reinforcement, the square sections contained longitudinal reinforcement and square and octagonal transverse hoops, and the rectangular wall sections contained longitudinal reinforcement and rectangular hoops with or without supplementary cross ties. The longitudinal stress-strain behavior of the confined concrete was measured and compared with that predicted by a previously derived stress-strain model with allows for the effects of various configurations of transverse confining reinforcement, cyclic loading, and strain rate. The measured longitudinal concrete compressive strain when the transverse steel first fractured was also compared with that predicted by equating the strain energy capacity of the transverse reinforcement to the strain energy stored in the concrete as a result of the confinement. ASCE.