A novel anchorage system for strengthening slender RC columns with externally bonded CFRP composite sheets Wisam Aules 1 , Yasir M. Saeed ⇑ , Franz N. Rad 2 Department of Civil and Environmental Engineering, Maseeh College of Engineering and Computer Science, Portland State University, Portland, OR 97201, USA highlights  Pullout tests were conducted on three types of CFRP anchorage systems.  Three columns were tested under a combined axial and flexural cyclic loading condition.  The effectiveness of using the proposed CFRP strengthening technique was investigated.  The initial lateral stiffness, ductility, and strength of RC columns were improved.  The efficiency of the proposed anchor was compared with available anchorage systems. article info Article history: Received 30 August 2019 Received in revised form 10 January 2020 Accepted 12 February 2020 Keywords: Anchors CFRP Concrete Slender columns Retrofit Strengthening abstract Previous studies have shown that using externally bonded (EB) fiber reinforced polymer (FRP) is one of the most effective techniques for strengthening reinforced concrete (RC) structures. The current guideli- nes recommend using anchorage systems to prevent debonding failure. Strengthening RC columns for flexure, the use of an anchorage system is necessary to transfer the forces from the column to the foun- dation. In this study, three types of Carbon Fiber Reinforced Polymer (CFRP) anchors were tested under pullout loading. The best of the three anchors, based on the results of pullout tests, was used in strength- ening one RC column. Three half-scale specimens of RC columns were tested under a combination of con- stant axial and cyclic lateral load. As expected, the results showed that strengthening RC columns with lateral confinement only increased the ductility of the columns but did not have a major effect on the moment capacity or stiffness. However, the lateral stiffness, moment capacity, and ductility of the col- umns confined with CFRP and strengthened with longitudinal CFRP sheets anchored to the foundation using a proposed novel anchor exhibited significant improvements. Ó 2020 Elsevier Ltd. All rights reserved. 1. Introduction and background In general, the use of fiber reinforced polymer (FRP) materials in reinforcing, strengthening, and repairing concrete structures has been significantly increased in the past two decades [1–3]. FRPs can be made with glass GFRP, aramid AFRP, and carbon CFRP mate- rials. CFRP sheets is one of the most commonly used material for strengthening concrete members. CFRP sheets have extremely high tensile strength (about 4 times stronger than that of conventional steel reinforcement) and high tensile modulus (about 75% that of steel) compared with other types of FRP materials. Typical tensile strength of CFRP is between 1200 and 2300 MPa, and typical ten- sile modulus of CFRP is between 100 and 150 GPa [4]. In seismi- cally active regions, and especially for older reinforced concrete (RC) moment frame buildings, the concern is almost always about the lateral performance of the columns. The current design code for RC buildings in the United States [5] requires that any column has to be stronger than the beams at any joint to ensure strong column-weak beam condition. Therefore, strengthening existing RC columns to meet the lateral load demands has gained a high level of importance. Much research has been done on strengthen- ing of RC columns using composite materials [6–8]. The conclu- sions often indicate that debonding controls the design [9–11].A special challenge occurs when FRP materials are used to transfer the load to another structural component where development https://doi.org/10.1016/j.conbuildmat.2020.118423 0950-0618/Ó 2020 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: Department of Civil and Environmental Engineering, Portland State University, P. O. Box 751, Portland, OR 97207, USA. E-mail addresses: wisam.a.aules@tu.edu.iq (W. Aules), yasir@pdx.edu (Y.M. Saeed), franz@pdx.edu (F.N. Rad). 1 Department of Civil Engineering, Tikrit University, P. O. Box 42, Tikrit, Salah Al- Din 34001, Iraq. 2 Civil and Environmental Engineering, Arthur M. James Professor of Structural Engineering, Department of Civil and Environmental Engineering, Portland State University, P. O. Box 751, Portland, OR 97207, USA. Construction and Building Materials 245 (2020) 118423 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat