Confining of square RC columns with FRP sheets using corner strip–batten technique Davood Mostofinejad, Elaheh Ilia ⇑ Department of Civil Engineering, Isfahan University of Technology (IUT), Room 341, Isfahan 84156-83111, Iran highlights  Corner strip–batten method was proposed for FRP confinement of square RC columns.  The performance of the proposed method was compared with other confining methods.  FRP rupture point in both IVS-B and IVS-IW methods was observed at middle of sides.  The maximum increase in bearing capacity was observed in IVS-B and IVS-IW methods. article info Article history: Received 14 October 2013 Received in revised form 18 June 2014 Accepted 23 July 2014 Keywords: Confinement CFRP composite Square RC column Corner strip Batten Uniaxial compression abstract The application of fiber reinforced polymer (FRP) composites has been successfully promoted for external strengthening of reinforced concrete (RC) columns. Recent studies showed that when these jackets are formed in a wet lay-up process for confinement of columns, an average rupture strain of FRP in specimens substantially fall below those of flat coupon tensile tests. The problem is more important in rectilinear columns because of premature rupture of FRP at corners due to stress concentration. In this paper, a new method is introduced for confinement of square concrete columns as using FRP strips at corners and FRP battens at sides. In this method, FRP battens do not experience any curvature in confining of section and are stretched as completely flat strips similar to flat coupons. To compare the new proposed method with other FRP-confining techniques, sixteen square RC columns with 133  133 mm cross section and 500 mm height were experimentally tested under uniaxial compression. The test parameters included continuity or discontinuity of corner strips along height of column, the vol- ume of fibers used, and the number of confining layers. The experimental results clearly demonstrated that confining battens in the new method of corner strip–batten are uniformly stretched under the ten- sion stresses of confinement; therefore, more uniform distribution of confining pressure on section occurs and the stress concentration at corners is eliminated. Thus, in the proposed method, better perfor- mance of FRP in confinement was observed and the compressive behavior of the strengthened column was significantly improved compared to those confined using conventional FRP wraps. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction The use of fiber reinforced polymer (FRP) composites has been recognized as an effective technique for repair and strengthening of reinforced concrete (RC) structures. Among the applications of FRP composites is their use as external confining jackets in retrofit of existing reinforced concrete (RC) columns; which increases both load carrying capacity and ductility of column. Based on experimental observations, the failure of the concrete column confined with FRP, dominates by the hoop rupture of com- posite when the overlap length is sufficiently provided [1–4]. Therefore, in column specimens with FRP rupture failure mode, the ultimate state of confined concrete is affected by the ultimate tensile strength and strain of composite measured in experimental tests. Recent studies have shown that the ultimate rupture strain of composite obtained in FRP confined concrete specimens is much smaller than the ultimate strain obtained from flat coupon tensile tests; which shows that the full tensile capacity of composite is not effectively used in confinement. Several reasons have been sug- gested for the difference between FRP ultimate tensile strain obtained from coupon tests and measured in FRP confined concrete http://dx.doi.org/10.1016/j.conbuildmat.2014.07.073 0950-0618/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +98 311 391 3818; fax: +98 311 391 2700. E-mail addresses: dmostofi@cc.iut.ac.ir (D. Mostofinejad), e.ilia@cv.iut.ac.ir (E. Ilia). Construction and Building Materials 70 (2014) 269–278 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat