Analytical Design Model for Reinforced-Concrete Beams Strengthened in Shear Using L-Shaped CFRP Plates Amir Mofidi 1 ; Omar Chaallal, M.ASCE 2 ; and Yixin Shao 3 Abstract: This paper presents the results of an analytical study on reinforced concrete (RC) T-beams strengthened in shear with L-shaped fiber-reinforced polymer (FRP) plates. The main objective of this study is to develop design equations for RC beams retrofitted in shear using L-shaped FRP plates, considering all possible modes of failure in ultimate limit states. Unlike RC beams strengthened with externally bonded (EB) FRP plates and fabrics, prefabricated L-shaped plates feature unconventional failure modes because of their special shape and anchor- age. The possible failure modes for RC beams strengthened with L-shaped FRP plates are (1) concrete breakout at the embedded part of the FRP plate in the flange; (2) FRP pull-off at the epoxy/FRP interface; (3) FRP pull-off at the concrete/epoxy interface; and (4) FRP overlap failure at the beam soffit. These failure modes do not occur in RC beams shear-strengthened with EB FRP fabrics and plates. Therefore, the existing design models for EB FRP fabrics and plates cannot predict with sufficient accuracy the contribution of FRP to the shear resistance of RC beams shear-strengthened with L-shaped plates. In this article, new design equations are proposed in light of recent developments and data. These equations distinguish the failure mode and calculate the FRP contribution to the shear resistance of RC beams strengthened with L-shaped FRP plates. In some cases, full embedment of the L-shaped carbon FRP (CFRP) plates in the RC beam flange is not feasible because of the presence of an obstacle (e.g., longitudinal reinforcing steel bars in the flange). The new design equations are applicable to RC beams strengthened with L-shaped FRP plates with different embedment lengths (including no embedment) of the CFRP plates in the RC beam flange. The proposed design equations are validated against experimental data collected from the literature. DOI: 10.1061/(ASCE)CC.1943- 5614.0000433. © 2013 American Society of Civil Engineers. Author keywords: Concrete beam; Fiber-reinforced polymer; Strengthening; Shear; Epoxy bonding; Debonding; Embedment; L-shaped plates; Design equations. Introduction Recently, significant interest has been shown in the application of fiber-reinforced polymer (FRP) composites for strengthening and repair of existing reinforced concrete (RC) beams. During the past two decades, several valuable research studies have been completed on the shear-strengthening of RC beams with FRP composites using different methods. These methods include externally bonded (EB) FRP sheets, near-surface mounted (NSM) FRP rods, and embedded-through section (ETS) FRP rods (e.g., Uji 1992; Chaallal et al. 1998, 2011; Khalifa et al. 1998; Triantafillou 1998; De Lorenzis and Nanni 2001; Galal and Mofidi 2010). Meanwhile, to obtain a better insight into the behavior of FRP sheets and rods bonded to concrete members, a large number of pull-off tests have been conducted worldwide (e.g., Maeda et al. 1997; Brosens and van Gemert 1999; Blaschko 2003; Seracino et al. 2007a). This undertaking has been particularly valuable for shear- strengthening, in which bonding is critical. Based on experimen- tal results, several bond models have been proposed to predict the bond behavior of FRP/concrete joints for EB FRP sheets, NSM FRP rods, and ETS FRP rods (e.g., Neubauer and Rostásy 1997; Maeda et al. 1997; Chen and Teng 2001; Blaschko 2003; De Lorenzis 2004; Yao et al. 2005; Seracino et al. 2007b; De Lorenzis and Teng 2007; Mofidi et al. 2012b). The FRP/concrete bond models have helped researchers to propose design equations for RC beams strengthened in shear with FRP composites by means of EB FRP sheets, NSM FRP rods, and ETS FRP rods (e.g., Khalifa et al. 1998; Chen and Teng 2003; Monti and Liotta 2006; Rizzo and De Lorenzis 2009; Mofidi and Chaallal 2011a; Mofidi et al. 2012b). However, there are very few research studies on the behav- ior of adhesively postinstalled embedded (APE) FRP plates bonded to concrete members. In particular, to the authors’ knowledge, no studies on the bond strength of L-shaped FRP plate/concrete joints are available, and few investigations have been carried out on the retrofit of RC beams in shear with L-shaped FRP plates. Meier (1998) experimentally investigated the strength of L- shaped FRP/concrete joints. Experimental tests on RC beams strengthened with L-shaped plates under static and cyclic loadings have been reported in Czaderski (1998), EMPA Report No. 116/7 (Eidgenössische Materialprüfungs und Forschungsanstalt (EMPA) 2002), Czaderski and Motavalli (2004), Robertson et al. (2007), and Chen and Robertson (2004). Mofidi et al. (2013) reported the experimental results of shear-strengthened RC beams using FRP L-shaped plates with different embedment lengths of the L-shaped plates in the RC beams’ flange. 1 Postdoctoral Fellow, Dept. of Civil Engineering and Applied Mechanics, McGill Univ., 817 Sherbrooke West, Montreal, QC, Canada H3A 0C3. E-mail: amir.mofidi@mail.mcgill.ca 2 Professor of Construction Engineering, Univ. of Quebec, École de Technologie Supérieure, 1100 Notre-Dame West, Montreal, QC, Canada H3C 1K3 (corresponding author). E-mail: omar.chaallal@etsmtl.ca 3 Associate Professor, Dept. of Civil Engineering and Applied Science, McGill Univ., Sherbrooke West, Quebec, Canada H3A 0C3. E-mail: yixin .shao@mcgill.ca Note. This manuscript was submitted on May 21, 2013; approved on August 7, 2013; published online on August 10, 2013. Discussion period open until March 8, 2014; separate discussions must be submitted for individual papers. This paper is part of the Journal of Composites for Construction, © ASCE, ISSN 1090-0268/04013024(8)/$25.00. © ASCE 04013024-1 J. Compos. Constr. J. Compos. Constr. 2014.18. Downloaded from ascelibrary.org by MCGILL UNIVERSITY on 07/22/14. Copyright ASCE. For personal use only; all rights reserved.