Evaluation of Existing Stress-Strain Models and Modeling of PET FRP-Confined Concrete

The compressive response of confined concrete greatly depends on the mechanical properties of the confining material. Based on these materials, various stress-strain models have been proposed in the past. Among these materials, the use of fiber reinforced-polymer (FRP) composites is now considered a promising solution to improve the overall behavior of confined concrete. New materials are being developed and used in seismic strengthening/retrofitting applications. Without experimental evidence, applicability of existing stress-strain models to new confining materials with different mechanical properties remains questionable. In this paper, existing stress-strain models which were mostly developed for steel and other FRPs with high elastic modulus and low rupture strain were assessed in predicting the ultimate condition of concrete confined by polyethylene terephthalate (PET) FRP, which is a newly developed material with low elastic modulus and large rupture strain (LRS). The ultimate strength was predicted well by some of these models; however, the ultimate strain could not be well predicted. Regarding the prediction of ultimate strain, some of those models which considered the axial strain capacity of FRP performed relatively better. Considering this discrepancy, a new simple stress-strain model is proposed for PET FRP-confined concrete, which not only considers the ultimate conditions but also the control points in the course of stress-strain path. Based on these control and ultimate points, stress-strain curves were generated using a well-known base curve. Finally, the proposed model was verified in predicting the ultimate condition of existing test data of PET FRP-confined concrete.