An accurate stress-strain model for FRP-confined concrete based on a novel approach

Accurate modeling of the complete stress-strain relationship of confined and unconfined concrete is of vital importance in predicting the overall flexural behavior of reinforced concrete structures. The analysis-oriented models, which utilize the dilation characteristics of confined concretes for stress-strain relationship prediction, are well recognized for their versatility in such modeling applications. However, the assumption adopted by this type of models, that the axial compressive stress and strain of fiber reinforced polymer (FRP)-confined concrete at a given lateral strain are the same as those in concrete actively confined with a confining pressure equal to that supplied by the FRP shell, has recently been demonstrated experimentally to be inaccurate for high-strength concrete (HSC). The results of the said experimental study indicate that, under the same conditions, FRP confinement provides a lower strength enhancement for HSC compared to that provided by active confinement. To develop an accurate model that can describe the experimentally observed behavior, two large test databases were used to closely investigate the relationships between the axial stress-strain behaviors of companion actively confined and FRP-confined concretes. Based on these observations a new approach is developed to establish the axial stress difference between the actively confined and FRP-confined concretes. Finally, a unified model is proposed to describe the stress-strain relationships of actively confined and FRP-confined concretes.