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.
Summary.A new model for eccentrically loaded FRP confined concrete or reinforced concrete columns is presented. With the aid of this model we wish to predict the experimental data and to explain the behavior of confined columns under eccentric loading.
In this article, a new model for eccentrically loaded FRP-confined circular concrete columns is presented. The cross-section is built up by 2D finite elements (where the variation of the stresses and strains is 3D), and the concrete modeled by a confinement-sensitive (non-associated) material law. The numerical solution of this model showed agreement with the experimental results available in the literature. It is shown that the maximum axial stresses in the cross-section -despite of the big differences in the radial-and hoop confinement stresses -are about the same for concentric and eccentric loadings. It is also shown that the recommended stress-strain curves available in the literature may lead to non-conservative results for eccentric loading, and -based on our numerical calculations -new stress-strain curves are recommended.
In this article, a model recently published by the authors is applied for the calculation of the axial resistance of centrically loaded fiber-reinforced plastic-confined rectangular concrete columns. The calculated results of our model agree well with the experimental data found in the literature. It is shown that the stiffness of the confinement has a much stronger effect on the strength than for the case of circular cross sections. Based on the numerical results, a simplified model is introduced which can be used in engineering practice.
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