Lateral response of PET FRP-confined concrete

The passive confinement of externally wrapped fiber-reinforced polymer (FRP) composites can effectively restrain the unstable lateral expansion of confined concrete, hence results in significantly improved strength and ductility. Unlike uniform lateral expansion in circular columns, concrete expansion is highly variable around the cross-section perimeter in non-circular columns. In case of seismic retrofitting, where the ductility enhancement is of prime concern, bulging of concrete on flat sides and premature failure of FRP around the sharp corners usually limit the confinement effectiveness because of limited strain capacity of commonly used FRP composites. Most recently, new FRP composites and fiber ropes have been developed which possess large rupture strain (LRS) capacity. Concrete expansion under the restraining mechanism of such LRS materials' confinement, particularly in non-circular columns, is hitherto unclear and should be investigated in detail for a reliable structural design. For this purpose, results of an experimental study on the lateral behavior of circular and non-circular concrete specimens confined by polyethylene terephthalate (PET) FRP, which possesses a LRS capacity, are presented and discussed in this paper. The parameters considered were the cross-sectional shape, the corner radius, and the number of FRP layers. Axial stress-lateral strain and lateral strain-axial strain relationships are presented to deeply understand the dilation of confined concrete. The experimental results showed remarkable influence of the considered parameters on the dilation of confined concrete. Different lateral expansions measured in different directions of non-circular specimens revealed important insights, which are responsible for the distribution of confining stress around the perimeter of such cross sections. In addition, predictions of lateral strain-axial strain response by some existing models were compared with the experimental results of PET FRP-confined circular specimens of this study. The comparison shows that these models were unable to predict well the lateral strain-axial strain response and need further modification.