Experiments on the residual load-bearing capacity of prestressed confined concrete columns

This paper is an experimental study of the prestressed external confinement (as opposed to the unstressed external confinement) of concrete compression members as a means of influencing load-deformation behaviour and residual capacity. Residual capacity is understood to be the load which can be absorbed in the event of ineffective or removed external confinement by a column which has previously been subjected to high loading in a confined state. The prestress and tensile stiffness of the confinement, as well as the loads on the confined system, were systematically varied in order to evaluate influences on residual capacity. 45 cylindrical confined specimens, as well as reference specimens, were subjected to concentric and eccentric, single and cyclic loading. The experiments confirmed the beneficial influence of confinement prestressing on concrete residual capacity. Prestressed confinement proved to be particularly effective in the case of cyclic loading and low confinement modulus, especially when compared to the unstressed variant. Analysis of the experimental results goes on to show that safety considerations are indispensable in the case of ineffective unstressed external confinement.