Analytical Model for Concrete Confinement in Tied Columns

An analytical model for the confinement mechanisms in tied columns has been developed. The model is based on the test results reported previously. A complete stress-strain curve for confined concrete is proposed. The strength of the confined concrete is calculated by using the concept of the effectively confined concrete area within the nominal concrete core. The area of the effectively confined concrete is determined by the tie spacing, the distribution of longitudinal steel around the core perimeter and the resulting tie configuration. According to the model, better distribution of longitudinal steel and smaller tie spacing result in higher strength and ductility of concrete. Other variables examined include the volumetric ratio of lateral reinforcement and the characteristics of steel. The results from the model agree well with the test results. Practical examples demonstrating the application of the model have been presented. Building code requirements for confinement are examined and it has been concluded that in certain circumstances the Codes provisions may be unsafe, while in others they may be unnecessarily conservative.