A theoretical model is developed to describe the uniaxial stress-strain relationship of spirally confined concrete. As well as using one single spiral, concrete confined by two interlocking spirals is also studied, using a finite element model to determine the magnification factors caused by multiple confinement. Predictions for the behavior of compression specimens with various types of reinforcement are given. Methods of determining the behavior of concrete in the compression zone of beams in flexure, which are subjected to strains that vary through the depth, are also presented. Experimental verification is not presented herein but has been carried out and is referred to in other work.[PUBLICATION ABSTRACT]