Journal of Engineering Science and Technology Review 12 (4) (2019) 60 - 68 Research Article Viability of Utilizing CFRP Composites for Improving the Structural Behavior of Steel Beams Khairedin M. Abdalla * , Ghazi Abu-Farsakh, and Montaha Al-Shdiefat Department of Civil Engineering, Jordan University of Science & Technology, Jordan Received 21 April 2019; Accepted 12 September 2019 ___________________________________________________________________________________________ Abstract This paper presents an experimental investigation to evaluate the viability of utilizing carbon fiber reinforced polymer (CFRP) composites for strengthening of indeterminate steel beams. Ten steel I-beams were strengthened using unidirectional CFRP composites in a form of plates attached on the flanges and/or web. The beams were tested as fixed- ends under a one center load distributed over the piston area. The indeterminate steel beams having two fixed ends required high load to cause failure. Although, the maximum load carrying capacities were not significantly improved due to debonding of the CFRP plates, but the strengthened-beams demonstrated reasonable improvement in the flexural-stiffness and slight increase in the torsional-stiffness. In most cases, the governing buckling-mode for the strengthened and un- strengthened beams was inelastic lateral-torsional buckling combined with local flange- buckling. The findings of this study show encouraging enhancement in the structural behavior of intermediate steel beams after strengthening with CFRP composites. This study provides an important guidance for future research toward development of means to realize the full potential use of CFRP composites for strengthening of steel beams. Keywords: Strengthening, CFRP composites, indeterminate steel beams, flexural stiffness ____________________________________________________________________________________________ 1. Introduction Structural steel and reinforced concrete structures are employed in construction daily all over the world, and the infrastructure and construction are ever proliferating and developing. Large number of structures becomes unsafe to use or deteriorates on a daily basis owing to changes in design configurations, loading, the use of low-quality building materials, and/or due to natural events like earthquakes. It is more economical to repair and retrofit the deteriorating components than replacing the entire structure. Moreover, in certain cases as in bridges, the process of strengthening and rehabilitation take less time and reduce the possibility of service interruption. The rehabilitation and strengthening processes were traditionally performed through attachment of steel plates, but this process is recently achieved by the use of CFRP composites if a form of sheets, strips, or plates [1- 7]. Over the past few years, the material strength and stiffness characteristics of the CFRP sheets improved greatly [8]. Recently, some types of CFRP composites have almost double elastic modulus of structural mild-steel (Figure 1). Also, the advantages of corrosion resistance and light weight of CFRP composites over steel in highly corrosive environments make them more effective such as in off-shore structures [9]. In-service characteristics of the CFRP composites made them a good choice for rehabilitation of damaged bridge box girders, because of their excellent fatigue and strength properties. Their high strength-to-density ratio made them excellent choice for retrofitting/strengthening of steel beams and structures [10]. Variations of the mechanical characteristics of CFRP composites and their effect on the strengthened systems under various environmental and loading conditions were studied [11]. The authors studied retrofitting and strengthening of double-strap joints of corroded steel plates under tension and also, they investigated the flexural performance of deteriorated steel I-beams using externally bonded CFRP composite plates [11]. The strengthened beams with CFRP plates experienced limited ductility upon failure; either by debonding or rupture, at higher load capacities than those of the unstrengthened beams [12]. Fig. 1 Comparison of stress–strain relations of mild steel, CFRP, and GFRP composites [9] Narmashiri et al. [12, 13] evaluated the load-carrying capacities of strengthened steel I-beams, which increased with increased length and thickness of the CFRP plates. The use of short CFRP plates led to premature end-debonding, Strain, % 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Stress, MPa 0 500 1000 1500 2000 2500 3000 High modulus CFRP Intermediate modulus CFRP High strength CFRP GFRP Mild steel JOURNAL OF Engineering Science and Technology Review www.jestr.org Jestr r ______________ *E-mail address: abdalla@just.edu.jo ISSN: 1791-2377 © 2019 School of Science, IHU. All rights reserved. doi:10.25103/jestr.124.07