Axial and lateral stress-strain model for concrete-filled steel tubes

The confining stress acting on the concrete in a concrete-filled steel tube is dependent on the lateral strain of the confined concrete whilst the lateral strain of the confined concrete is dependent on the confining stress. Hence, the lateral strain and confining stress are inter-related. Up to now, it remains a difficult task to evaluate the lateral strain of concrete confined by a steel tube and the confining stress acting on the concrete. To resolve this problem, a theoretical model for evaluating the lateral strain and confining stress in a concrete-filled steel tube system at various stages of loading is developed. The theoretical model is first applied to analyze concrete-filled steel tube specimens tested by other researchers to verify its accuracy and then used to work out the required thickness-to-diameter ratios of steel tubes for achieving different levels of ductility.