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Five large circular reinforced concrete columns confined by spiral reinforcement in accordance with the provisions of the draft of the New Zealand Concrete Design Code were tested under reversed cyclic bending combined with various axial load levels. Results of load-deflection hysteresis loops, curvature distributions, and confining and shear steel strains are presented. Substantial enhancement of flexural and shear strength values (above those predicted using normal ultimate strength theory) was obtained. A method for predicting confined moment capacity is suggested.
Priestley et al. (Thu,) studied this question.