Behavior of Laterally Reinforced Concrete Columns

The results of an experimental and analytical investigation of the effect of non-uniform lateral confinement, such as that produced by closely spaced rectangular ties, on the behavior of concrete columns are presented. The main parameters studied were: flexural rigidity of lateral reinforcement, percentage of lateral reinforcement, concrete shrinkage, and strain rate. The effectiveness of lateral reinforcement, primarily depends on the flexural rigidity of the ties. The confining stress in columns with conventional rectangular ties is concentrated in the vicinity of the column corners and corresponds to the limiting state of confinement with corner forces. The stresses in the ties at maximum load are small and the concrete at some distance from the corners is nearly unconfined. Tie rigidity can be increased by cross bars welded to the ties. The added tie rigidity results in significantly increased ductility and, for small tie spacing in an appreciable strength increase. Comparisons are made with the results of other investigations, and a relation between strength increase due to ties and lateral reinforcement percentage is suggested.