Analytical model to predict axial stress-strain behavior of heat-damaged unreinforced concrete columns wrapped by FRP jacket

Abstract

Although there are several confinement models to obtain analytically the axial stress-strain response (fc − εc) of concrete columns wrapped with fiber-reinforced-polymer (FRP) jacket at ambient conditions, a reliable designoriented model to determine the fc − εc of heat-damaged concrete columns post-confined with FRP is still lacking in the literature. This study aims to address this research gap, by proposing a formulation that predicts the favourable effects of FRP confinement on concrete elements previously exposed to high temperatures. This model proposes a closed-form formulation to derive a fc − εc expression, including a set of strength and strain submodels to calculate the stress/strain information at transition and ultimate points defining the stress-strain response. To develop the model and calibrate its key components by data analysis of statistical treatment techniques, a large test database of FRP confined unheated/heat-damaged concrete of circular/square crosssection consisting of 1914 specimens was collected. The proposed design-oriented model is able to demonstrate the influence of pre-existing thermal damage on the axial fc − εc relationship, whose reliability is revealed comprehensively through predicting data from several experimental heat-damaged concrete specimens confined with FRP systems.