In this article, a new model for FRP-confined circular concrete columns based on a sophisticated material model is presented. With the aid of this model the effect of the stiffness of the confining material on the strength of the structure was investigated. It was found that: (i) in the case of a wide parameter range (low-stiffness confinement) the stiffness has a minor effect on the concrete strength; (ii) in the case of high-stiffness confinement a significant gain in concrete strength can be reached by taking into account the confinement stiffness; and (iii) in theory the concrete can be overconfined (with a lower strength); however, this case is not realistic for conventional FRP. Based on the new model an analytical expression is derived to determine the (lower limit of) strength of confined concrete, and the limit of insufficient confinement is also derived. The results are verified by experiments available in the literature.
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