An Investigation of Interfacial Stresses in Reinforced Concrete Beams Using FRP Laminates Baris Sayin 1 and Ekrem Manisali 2 1 Construction Works & Technical Department, Istanbul University, Istanbul, Turkey 2 Department of Civil Engineering, Faculty of Engineering, Istanbul University, Istanbul, Turkey Reinforcement of reinforced concrete (RC) beams against bending through utiliza- tion of bonded fibre-reinforced plastic (FRP) laminates has been accepted as an effective method of strengthening. In this study, the effects of FRP reinforcement over the parameters of interfacial stresses in reinforced concrete beams were exam- ined both experimentally and numerically. Essentially, the main goal of the study was to investigate quantitatively the behaviour of the RC beams strengthened with adhesively bonded FRP. In order to achieve this goal, an experimental study was initially carried out. Afterwards, the ANSYS 1 WB finite element program was employed to model and analyze the RC beams externally bonded to FRP. The obtained results are expected to demonstrate the main characteristics of interfacial stress distributions inside beams strengthened with FRP. The evaluation of inter- facial stresses provides the basis for understanding the main characteristics in such beams and for developing suitable design rules. Keywords: Adhesive; Fibre reinforced plastic (FRP); Finite element analysis; Interfacial stresses; Reinforced concrete (RC) beam 1. INTRODUCTION For more than 15 years, strengthening of reinforced concrete (RC) beams in flexure by adhesive bonding of a fibre reinforced plastic (FRP) laminate to the tension face has become an accepted and general method due to the favourable mechanical properties of FRP composites. Externally bonded FRP reinforcement has been shown to Received 7 December 2009; in final form 20 July 2010. Address correspondence to Baris Sayin, Construction Works & Technical Depart- ment, Istanbul University, Fatih, Istanbul 34116, Turkey. E-mail: barsayin@ istanbul.edu.tr The Journal of Adhesion, 86:1132–1157, 2010 Copyright # Taylor & Francis Group, LLC ISSN: 0021-8464 print=1545-5823 online DOI: 10.1080/00218464.2010.519260 1132