Strength and Behavior of Spirally Prestressed Concrete Cylinders under Eccentric Loading

摘要

An investigation was made of three inch diameter by twelve inch long concrete cylinders prestressed with high strength steel spirals. The results of the experimental work are given and the behavior of the cylinders under the application of axial and eccentric loads are described. Sixty-eight spirally wrapped cylinders were tested during this investigation. The variables considered were (1) percentage of spiral reinforcement (2) initial prestress in the spiral reinforcement and (3) eccentricity of loading. It is shown that (1) the principal effect of the initial prestress in the spiral reinforcement was to alter the initial stiffness of the cylinder (2) the initial prestress in the spiral reinforcement had no corresponding significant effect upon the ultimate load capacity and (3) the primary result of varying the percentage of spiral reinforcement was to alter the lateral restraint of the concrete so that it could develop its strength to different degrees in a gradual type of compression or tension failure depending upon the eccentricity of the loading. The ultimate load formulas for compression and tension type of failures in the current ACI Building Code (ACI 318-63) are modified to include the contribution by the spiral reinforcement to the ultimate load. (Author)