Analysis-oriented stress-strain model of CRFP-confined circular concrete columns with applied preload

The compressive behavior of FRP-confined concrete is a current issue in the field of structural retrofitting. The available models well predict the stress-strain behavior under monotonic and cyclic loads. However, in the practical applications, columns that need an increasing of bearing capacity are often strengthened under serviceability load conditions, with a stress and strain state that could change the response of the reinforced systems with respect to the case of the unloaded state. In this paper, the compressive behavior of circular FRP-confined concrete columns with preload is analyzed with the introduction of a modified analysis-oriented model. Differently from the classical formulations in which stress-strain model is aimed to the evaluation of the confinement capacity of non-preloaded elements in monotonic regime, the proposed model is also suitable for the determination of the combined response of unconfined and confined concrete subjected to an established stress/strain state in the unconfined state. The proposed model is also compared with the experimental results available in the literature under different assigned preloading levels.