Exploring GFRP bars as reinforcement for rectangular and L-shaped beams subjected to significant torsion: An experimental study A. Deifalla a,⇑ , M. Hamed b , Amin Saleh b , Tarek Ali c a Department of Civil Engineering, BUE, El Shorouk City, Egypt b Department of Civil Engineering, Ain Shams University, Cairo, Egypt c Department of Civil Engineering, Helwan University, Cairo, Egypt article info Article history: Received 13 July 2013 Revised 20 November 2013 Accepted 21 November 2013 Keywords: GFRP bars Bonded GFRP stirrups Bent GFRP stirrups and L-shaped beams abstract Steel corrosion related problems have been a heavy burden on countries economically and socially for many decades. Therefore, the inevitable quest to find an alternative for steel reinforcements is long over- due. On the other hand, fiber reinforced polymer (FRP) bars have non-corrosive nature and could be the solution for this problem. In this study, the objective is exploring the usage of glass fiber polymer (GFRP) bars as torsion reinforcement for L-shaped beams. New adhesively bonded GFRP stirrups are presented and implemented. Five beams were constructed and tested under significant torsion. The bonded GFRP stirrups were more effective as transversal reinforcement compared with the bent steel stirrups and the bent GFRP stirrups. It improved the ultimate torsional strength and increased the corresponding unit angle of twist and the maximum stirrup strain as well as the major concrete crack width. In addition, the increase in the GFRP transversal reinforcement percentage improved the ultimate torsional strength, the toughness, and the deformability. Moreover, the usage of a stirrup strain value of 0.4% resulted in overly conservative predictions for the ultimate torsional resistance; however, it provided adequate torsional deformability index and toughness. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Long-term durability and extended service life of reinforced concrete (RC) structures have become a major concern in the con- struction industry. The sustainability of aging infrastructure can only be achieved through continuous maintenance. During this maintenance, many reported problems are related to steel corro- sion [1]. Deficient RC structures can be repaired using FRP fabrics as external reinforcements [2,3]. However, the emerging economy demands that new infrastructure performs more efficiently with respect to corrosion related problems. An excellent approach to fulfill this demand is to examine new alternatives that are less likely to corrode. Fiber reinforced polymer (FRP) bars promise bet- ter performance as internal reinforcements for new construction because of their superior performance over steel re-bars in terms of corrosion (thus reducing related maintenance and repair costs), transportation, handling, and installation. Since 1995, extensive studies have been conducted on the flex- ural and shear behavior of concrete beams internally reinforced with FRP [4,3,5,6]. However, shear design provisions of beams internally reinforced using FRP bars are not yet fully developed [7–9]. Although researchers have investigated the torsional behav- ior of beams externally reinforced with FRP [10–12], the torsion behavior of beams internally reinforced with FRP has not received much attention. To our knowledge, only one limited experimental study exists in the available literature [13] and two finite element studies [14,15]. The American Concrete Institute Committee 440 noted that manufactured FRP bars could only be bent using heat and pressure if manufactured with thermo-plastic resin [5]. In addition, It was indicated that FRP bars can be manufactured with bends; however, a strength reduction of 40–50% (compared with the tensile strength of a straight bar) can occur in the bent portion due to fiber bending and stress concentration. In 2009, Shehab et al. conducted an experimental investigation of the torsional behavior of FRP reinforced concrete beams [13]. Sixteen rectangular beams reinforced by glass FRP (GFRP) and con- ventional steel bars were constructed and tested under torsion. Different reinforcement details were also implemented. It was determined that GFRP bars are very difficult to bend into stirrups. In addition, the bond between the stirrups and the concrete at the corners was weak, causing a significant loss in strength. During the bending process (even with gentle heating), fibers on the outside of the bend were overstressed and those on the inside buckled. Table 1 shows a summary of the typical details of the tested beams and the experimental results. The reported experimental results 0141-0296/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.engstruct.2013.11.027 ⇑ Corresponding author. Tel.: +20 1009990640. E-mail addresses: diffalaf@mcmaster.ca, ahmed.deifalla@bue.edu.eg (A. Deifalla). Engineering Structures 59 (2014) 776–786 Contents lists available at ScienceDirect Engineering Structures journal homepage: www.elsevier.com/locate/engstruct