PSI - Issue 28

Haya H. Mhanna et al. / Procedia Structural Integrity 28 (2020) 811–819 Mhanna et al./ Structural Integrity Procedia 00 (2020) 000–000

812

2

1. Introduction Many reinforced concrete (RC) structures need to be retrofitted to increase its capacity, stiffness, and durability. Repairing structures via applying externally bonded fiber-reinforced polymer (EB-FRP) reinforcement has proven to be effective and convenient (Choobbor et al. (2019); Helal et al. (2020); Naser et al. (2019); Nawaz et al. (2016); Salama et al. (2019)). Compared to existing strengthening techniques, such as, section enlargement and addition of steel plates, EB-FRP offers several advantages including high strength, quick installation, durability, and versatility. FRP can be applied onto the RC beams’ tension side to enhance its flexural capacity or onto the side face of the beams in the form of side bonded, U-Wraps, or closed wraps to enhance its shear capacity. Numerous studies investigated different parameters affecting the contribution of externally bonded FRP reinforcement to the shear strength of RC beams (Abuodeh et al. (2020); Hawileh et al. (2015); Lee et al. (2017); Ozden et al. (2014)). These parameters include span-depth ratio, FRP types, different FRP layouts and configurations, steel transverse reinforcement, and the amount of the FRP materials. These studies proved that the use of FRP for strengthening RC beams in all forms enhances the shear capacity of beams, and in particular the case of completely wrapped scheme, the composite sheets also enhances the beam’s ductility. However, completely wrapping the beams is not feasible in most applications, due to geometrical obstructions, such as presence of slabs over beams. Therefore, completely wrapping scheme is the most used form of shear strengthening. Despite its advantages, the main drawback of EB-FRP technology is the premature debonding of the FRP laminates prior to utilizing the full tensile strength of the laminates and typically results in a brittle failure (Ali et al. (2014); Hawileh et al. (2014); Mhanna et al. (2019); Mostofinejad et al. (2016); Mohamed et al. (2018); Naser et al. (2012)). To overcome this problem, techniques to increase the bond length such as various laminates configurations and different types of anchors have been extensively studied (Bae and Belarbi (2013); Eshwar et al. (2008); Hawileh et al. (2019); Kalfat (2016); Kim et al. (2015); Kalfat et al. (2013); Karam et al. (2017); Smith et al. (2013)). While most of these solutions resulted in various levels of improvement in the EB-FRP systems, FRP splay anchors has shown promising results in terms of enhancing the capacity and ductility of the strengthened members. FRP anchors are made up of bundle fibers in which one end is inserted into a predrilled hole (dowel component) and the other end is splayed onto the laminate’s surface (fan component) to distribute the stresses. The key portion is the part of the anchor that connects the fan to the dowel. There are numerous advantages of FRP splay anchors as opposed to other anchorage systems. FRP anchors have better compatibility with the FRP laminates as they are made of the same material. In addition, the anchors can be designed to suit wide range of structural applications, such as, shear and flexural strengthening of RC beams and slab to column joints. FRP anchors are also noncorrosive and have high strength to weight ratios (Castillo, Kanitkar, et al. (2019); Singh et al. (2019)). There are two types of FRP anchors: straight anchors, where the dowel is inserted straight into the structure. This type of anchorage is subjected to tensile stresses. The other type of FRP anchors is bent anchors, where the anchors are installed at an angle, called insertion angle. This type of anchorage is subjected to tensile and shear stresses, hence, are less effective than straight anchors. Although straight anchors have improved the member’s capacity than bent anchors, it cannot be applied in many cases due to restrictions in member size or steel reinforcement spacing. Thus, it is important to study the effect of anchoring the laminates with bent FRP anchors. In general, there are five anchor failure modes that should be avoided in design to prevent limiting the strength of EB-FRP system. The FRP anchor failure modes as reported in the literature are concrete-cone failure, concrete-cone + bond failure, dowel pull-out, fan to-sheet debonding, and fiber rupture. Concrete-related failures and dowel pull-out failure are mostly affected by the hole diameter, embedment depth and concrete compressive strength. In addition, pull-out failure is affected by insertion angle, as in the case of bent anchors. Fan-to-sheet debonding failure is dependent on fan area and shear strength of the epoxy adhesive. Finally, fiber rupture failure is influenced by the tensile strength of FRP sheets, dowel cross-sectional area, fanning angle and insertion angle (Castillo, Dizhur, et al. (2019); Lluardó et al. (2017); Kim and Smith (2009)).