review and improvement of stress-strain models for frp-confined concrete

The cyclic stress-strain behavior of frp-confined concrete columns is a key aspect of their performance, particularly in the context of seismic retrofitting and design. significant research has been conducted in recent years to study the cyclic response of frp-confined concrete in both circular and rectangular columns subjected to unloading and reloading cycles. these studies have led to the development of various cyclic stress-strain models to predict the behavior of frp-confined concrete columns under such loading conditions.however, critical gaps remain in the modeling of early-stage unloading strains, reloading slope reduction, and cross-section-dependent behavior. this paper begins by introducing the fundamental components of cyclic stress-strain behavior. it then reviews and evaluates the existing models proposed for each aspect of this behavior, focusing on comparing their predictions with experimental data. furthermore, modifications are suggested for components of the cyclic models that exhibit discrepancies when validated against experimental observations. these include a proposed reloading slope factor and refined unloading path formulations. these improvements aim to enhance the accuracy and reliability of cyclic stress-strain models for frp-confined concrete columns, contributing to their effective application in structural design and seismic resilience.