The Residual Strength of Confined Concrete

Structural engineers have long recognised the importance of member ductility in the design of reinforced concrete members to overcome uncertainties in the design procedure as well as in absorbing energy due to dynamic loads such as earthquakes, impact and blast loads. This has lead to much research on quantifying the rotational capacities of reinforced concrete hinges where intrinsic to the analysis is the behaviour of the concrete compressive stress-strain softening branch, of which the residual strength and strain capacities are important parameters. Much of the softening branch research has been based on careful empirical analyses of confined concrete cylinders. This paper shows that shear-friction theory, which is an established area of research, can be used to quantify the residual strength of hydrostatically and spirally-reinforced confined concrete and provide a lower bound to the residual strength of FRP confined concrete. Hence shear-friction theory is shown to provide an additional structural mechanics tool in the analysis and application of confined concrete.