Compressive stress-strain model for high-strength concrete confined with spirals

The design of high-strength concrete columns under seismic loading is not only based on the maximum strength of the column but also the ductility of the column. A combination of the axial stress and strain of the column can be represented as the total amount of energy that the column can absorb before failure. An increase in the strength of the concrete core or increase in maximum strain before failure will increase the amount of energy that the specimen can absorb. For the design of circular column, the method to improve the amount of energy the column can absorb is based on the spacing of the transverse reinforcement used. This paper presents a stress-strain model to predict the axial behavior of high strength concrete confined with both single spiral and two opposing spirals. Data from twenty-one of high-strength concrete columns along with ten normal-strength concrete columns is presented and used to derive the model. To have an understanding of the correlation between the amount of transverse reinforcement and the strength of the concrete core, the range from the minimum spacing to the maximum spacing as specified by ACI-318 was considered. Also, the effect of the amount of longitudinal reinforcement was considered in deriving the model.