Contents lists available at ScienceDirect Structures journal homepage: www.elsevier.com/locate/structures Retrofitting external RC beam-column joints of an ordinary MRF through plastic hinge relocation using FRP laminates Mahmoud R. Maheri a, ⁎ , Ashkan Torabi b a Department of Civil Engineering, Shiraz University, Shiraz, Iran b Department of Civil Engineering, Islamic Azad University, Marvdasht Branch, Iran ARTICLE INFO Keywords: Seismic retrofitting RC frame Beam-column joint Cyclic testing Plastic hinge FRP Energy dissipation Flange and web-bonded ABSTRACT This paper presents the results of experimental and numerical investigations on flange and web -bonded FRP retrofitting schemes for external RC joints of moment resisting frames. Two, identical full-scale external joints are designed and constructed according to ACI318M-11 requirements for ordinary moment resisting frames. Quasi-static cyclic loading tests are then carried out on the specimens and some seismic performance parameters including strength, ductility, energy dissipation and stiffness are evaluated and compared. Numerical analyses are also carried out to study the effects of FRP overlay length on required number of plies for plastic hinge relocation and joint strength. It is found that successful relocation of plastic hinge away from the face of the column into the beam is possible with appropriate number of FRP laminate plies and overlay length. It is also found that as the length of the FRP laminate over the beam flange increases, the joint strength is enhanced; however, larger number of plies would be required for plastic hinge relocation. 1. Introduction In recent decades, retrofitting/repairing reinforced concrete struc- tural members, damaged or deemed deficient owing to change in their use or state of loading, has been the subject of different studies. In this regard, RC beam-column joints have received considerable attention due to their key role in stability and seismic performance of the structure. Several techniques have been proposed to retrofit RC joints including: shotcrete jacketing [1], cast-in-place concrete/RC jacketing [2], steel jacketing [3], stiffened steel plates [4] epoxy injection repair [5], applying near surface mounted fibre reinforced polymer (FRP) la- minates/bars [6] and using externally bonded FRP laminates [7–14]. Externally bonded schemes were first used by bonding steel plates with adhesive resins to the tension zones of concrete for increased flexural strength [15]. Externally bonded steel plates were also used at joints as connecting plates for retrofitting an RC frame with steel braces [16–22]. Using steel plates for these purposes has some drawbacks in- cluding: heavy weight, difficulties in installation and susceptibility to corrosion that reduces strength and deteriorates bonding. Superior advantages of FRP laminates over steel plates such as; high corrosion resistance, light weight, high strength and ease of application has made FRP to be an attractive alternative to steel plates. In post-earthquake inspections of damaged RC moment resisting frames, it has been ob- served that external beam-column joints are more prone to damage than the internal joints. Discontinuity of structural geometry and sub- standard confinement conditions in external beam–column joints make them more vulnerable to seismic loading compared to the internal beam–column joints [23–27]. Mosallam [28] conducted a pioneering study on strength and ductility of reinforced concrete moment frame connections strengthened with quasi-isotropic laminates. Prota et al. [29] proposed the use of carbon fibre reinforced polymer (CFRP) rods with externally bonded laminates to restore and rehabilitate deficient interior joints. Ghobarah and Said [30] conducted different tests on exterior joints reinforced with U-shaped and diagonal glass fibre re- inforced polymer (GFRP) layers. The deficient specimens were designed to fail in joint shear, conforming to a typical deficient beam-column joint designed per pre-1970 standards. Balsamo et al. [31] investigated the seismic performance of a repaired RC frame using flange and web- bonded CFRP laminates. Pantelides et al. [32] tested interior beam- column joints with different FRP retrofitting schemes such as web- bonded, U-wrapping and bottom-flange-bonded FRP composites. Their test results indicated that most of rehabilitation methods were suc- cessful in increasing strength and developing a plastic hinge on the beam. Alsayed et al. [33] carried out an experimental study on seismic response of web-bonded FRP exterior RC beam-column joints. The re- sults of the study confirmed the capability of carbon/epoxy composites in improving both strength and ductility of exterior beam-column joints. Dalalbashi et al. [10] compared the numerical results of three https://doi.org/10.1016/j.istruc.2019.08.004 Received 24 May 2019; Received in revised form 20 July 2019; Accepted 1 August 2019 ⁎ Corresponding author. E-mail address: maheri@shirazu.ac.ir (M.R. Maheri). Structures 22 (2019) 65–75 2352-0124/ © 2019 Institution of Structural Engineers. Published by Elsevier Ltd. All rights reserved. T