PSI - Issue 42

Jamal A. Abdalla et al. / Procedia Structural Integrity 42 (2022) 1223–1230 Abdalla et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction The use of fiber-reinforced polymers (FRP) to strengthen existing reinforced concrete (RC) and steel structures has eliminated many of the current infrastructure problems. This is due to its favorable properties such as high corrosion resistance, high strength, light weight, rapid installation time, lower life-cycle costs, durability, and sustainability (Mhanna et al. (2021a); Karam et a. (2017)). Such characteristics are vital to maintain the integrity of structures such as bridges and buildings. Introducing FRP in beams and columns is an effective way to enhance the RC beams in shear, flexure, and axial. Shear strengthening using FRP materials is crucial in many critical applications due to the severity of shear failures. In fact, shear failures are sudden and brittle with no signs exhibited prior failure. Shear strengthening using FRP can be accomplished by bonding the FRP sheets to the concrete substrate either in the form of complete wraps, U-jackets, or side bonded. Completely wrapping the FRP around the beams is the ideal strengthening method as it provides confinement as well as shear enhancement. In addition, the complete wrapping scheme develops the tensile capacity of the FRP (Alotaibi et al. (2020); Naser et al. (2019)). However, this method could be difficult to be implemented in many cases due to geometrical hindrance, such as, in cases where the RC beams are attached to slabs. As a result, placing the FRPs in the form of U-wraps is the most commonly used method. The efficiency of the U-wraps is often limited by the insufficient development length and consequently the interfacial bond strength between the FRP and concrete surfaces. The sided bonded scheme is rarely being used nowadays due to its ineffectiveness compared to other conventional methods (Saribiyik et al. (2021)). The primary failure mode of FRP-strengthened beams is the premature debonding of the FRP laminates from the concrete substrate, at low FRP strain levels without developing the full tensile strength of the FRP material (Abdalla et al. (2020)). To address this issue, research have shown that anchoring the U-wraps by means of adequately designed anchorage systems could delay or prevent debonding and develop the tensile capacity of the FRP (Pudleiner et al. (2019); Shekarchi et al. (2020)). Several types of anchorage systems were studied to mitigate debonding failure of the U-wraps, such as but not limited to, horizontal FRP strips (Kalfat et al. (2020)), mechanical anchorage (Abuodeh et al. (2021)), externally bonded reinforcement on grooves (EBROG) and on bores (Mohamed et al. (2020); Mohamed et al. (2018)), and FRP spike anchors (Mhanna et al. (2020)). Different types of anchors have resulted in different degrees of improvement in the FRP-to-concrete bond strength out of which FRP spike anchors have demonstrated the ability to achieve the tensile capacity of FRP strengthening material. Other advantages of FRP spike anchors include compatibility with the FRP laminates (as it is made of the same material) and it can be used for wide variety of structural applications, such as, beam to column joints (Alotaibi et al. (2019); del Rey Castillo et al. (2019)). There are several parameters that would affect the efficiency of FRP spike anchors, including embedment depth, dowel diameter, insertion angle, fan angle, AMR (anchor-material ratio) which is equal to the anchor cross-sectional laminate area divided by the laminate cross-sectional area of the strip, and fan length. The effect of these parameters on the capacity of the anchors has been addressed in several research studies. Sun et al. (2016) addressed the effect of concrete compressive strength, fan length (angle), width of the CFRP strip, and AMR ratio on the capacity of carbon FRP (CFRP) anchored concrete prisms. It was concluded that the bond between the FRP and concrete increased when using higher concrete strengths, resulting in increasing the load level at which the FRP strip debonded (by 10%). In addition, to rupture the CFRP strip, the AMR value should not be less than 2 and the maximum fan angle should be a 64 º . It was also found that wider CFRP strips lowered the average stress at rupture and caused higher local peak strains in the CFRP laminate. Similarly, Pudleiner et al. (2019) studied the effect of various anchor parameters on the flexural capacity of concrete prisms. The variables of the study were width of the CFRP strip, number of FRP layers, number of anchors per strip width, AMR ratio, anchor fan overlap length, and chamfer radius of the anchor hole. Several conclusions were drawn from this study. First, the fan length should increase proportionally with the number of FRP layers to develop the tensile capacity of the FRP sheet. Second, an AMR ratio of 2 and a chamfer radius of 1.4 times the hole cross-sectional radius was recommended. Finally, increasing the number of anchors per strip width improved the FRP sheet stress distribution. Several experimental investigations studied shear behavior of RC beams strengthened with FRP laminates and spike anchors. In a recent study by Mhanna et al. (2021a), the authors studied the effect of CFRP anchor embedment depth and fan length on the shear capacity of CFRP U-wrapped T-beams. It was observed that an anchor embedment length of 100 mm increased the shear capacity of the beams by 21% compared to the 50 mm embedment depth. Therefore, it was concluded to design the anchors with embedment depths equal to 6 times the dowel diameter. In addition,