Lateral response of PET FRP-confined concrete Shahzad Saleem a , Amorn Pimanmas b,⇑ , Winyu Rattanapitikon a a School of Civil Engineering and Technology, Sirindhorn International Institute of Technology, Thammasat University, Bangkok, Thailand b Department of Civil Engineering, Faculty of Engineering, Kasetsart University, Bangkok, Thailand highlights  Experimental results on the dilation of PET FRP-confined concrete were presented.  Confinement ratio, corner radius and cross-section shape were the variables of this study.  Concrete dilation was very high and significantly influenced by the considered variables.  PET FRP efficiently redistributed the concrete damage due to its large rupture strain.  Existing models were unable to predict well the lateral response and need further modification. article info Article history: Received 12 May 2017 Received in revised form 15 September 2017 Accepted 26 October 2017 Keywords: Circular Corner radius Lateral strain PET FRP-confined concrete Rectangular Square abstract 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 hith- erto 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 dee- ply 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. Ó 2017 Elsevier Ltd. All rights reserved. 1. Introduction To increase the strength and ductility of poorly detailed rein- forced concrete (RC) columns, particularly for seismic retrofitting, one of the widely accepted techniques is to confine the lateral expansion of concrete by wrapping with fiber-reinforced polymer (FRP) sheets in the hoop direction. After the formation of internal cracks, the Poisson’s ratio of concrete, which is in the range of 0.15–0.20 in elastic range, starts to increase before reaching the unconfined strength. As a result, concrete expands laterally at a faster rate nonlinearly. This unstable expansion of concrete exerts outward pressure on the confining device which induces hoop strain in the FRP wrap. Consequently, FRP wrap exerts inward https://doi.org/10.1016/j.conbuildmat.2017.10.116 0950-0618/Ó 2017 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: Department of Civil Engineering, Faculty of Engineering, Kasetsart University, Bangkok, Thailand. E-mail addresses: shahzad.saleem@uettaxila.edu.pk (S. Saleem), apimanmas@ yahoo.com (A. Pimanmas), winyu@siit.tu.ac.th (W. Rattanapitikon). Construction and Building Materials 159 (2018) 390–407 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat