PSI - Issue 68

Maha Assad et al. / Procedia Structural Integrity 68 (2025) 252–258 M. Assad et al./ Structural Integrity Procedia 00 (2025) 000–000

253

2

properties such as high strength-to-weight ratio, excellent corrosion resistance, and ease of application (Assad et al., (2022b), (2022a); Kaliyappan & Pakkirisamy, (2023); Salama et al., (2019); Zhang et al., (2024)). However, the effectiveness of CFRP strengthening systems is limited by the premature debonding failure of the CFRP laminates from the concrete substrate (Assad et al., (2024); Castillo et al., (2019); Zaki et al., (2019)). This reduces the ultimate load-carrying capacity of the strengthened beams. To mitigate this issue, CFRP anchorage systems have been developed to enhance the bond between the CFRP and concrete. Several previous studies highlighted the effectiveness of using CFRP spike anchors in delaying debonding failure and enhancing the overall performance of the strengthened beams (Abdalla et al., (2023); Abdalla et al., (2023); Mhanna et al., (2020), (2021)). CFRP spike anchors consist of a bundled fiber sheet, where part of the bundle -the dowel- is inserted into a hole in the concrete and the remaining part is splayed on the FRP sheet to form the fan, adhered to concrete. Many parameters related to the design of the CFRP anchor were found to influence the behavior of the CFRP-to-concrete anchored joint, namely, the anchor’s embedment depth and fan length, the fanning angle, anchor’s dowel diameter, and anchor’s inclination/insertion angle (Alshami et al., (2021); Hawileh et al., (2024); Pudleiner, (2016); Sun et al., (2020)). Straight anchor configurations are frequently employed in structural joints like beam-to-slab, slab-to-wall while bent anchors are used to secure FRP laminates in strengthened beams or slabs. Generally, the efficiency of straight anchors is better than bent anchors. This is due to the fibres being less well aligned with the direction of the applied force in the case of bent anchors. Hence, the anchors are subjected not only to tensile forces but also to shear forces. Zhang and Smith (2012) proposed an equation for the reduction coefficient for bent anchors compared to straight anchors, depending on the insertion angle. The insertion/inclination angle is the angle at which the anchor’s dowel is inserted in the concrete’s hole with reference to a horizontal line. In bent anchors, the angle is between 0º and 180º. The behaviour of CFRP anchors in FRP-to-concrete anchored joints was extensively studied by researchers through conducting single shear pull-off tests. Zhang et al. (2017) conducted a series of single shear tests of FRP strengthened concrete specimens with FRP anchors. Different insertion angles of FRP anchors were explored. Authors concluded that an anchor’s insertion angle of 135º provided the optimum performance. The anchor’s effect was also studied through bending tests by few researchers. Alshami et al. (2023) concluded that an insertion angle of 135º and 155º provided a significant capacity increase compared to the vertical anchors. When the anchor is bent at an angle of 135º, it is assumed that the tensile capacity is maximized, and the effect of shear stresses is minimized. One study performed by Mhanna et al. (2022) investigated the effect of insertion angle on the shear behaviour of RC T-beams. Authors found that small anchor inclination angles performed better in terms of enhancing the shear strength and ductility of RC T-beams than perpendicular anchors. However, to the best of the author’s knowledge, no previous studies were conducted on the effect of inclined anchors on the flexural strength of RC beams, especially those anchored with large anchors (diameter larger than 14 mm). In light of this, this study aims to investigate the effect of the anchor’s inclination angle on the flexural behaviour of strengthened and end-anchored RC beams. By assessing the overall performance at failure, load versus deflection curves, flexural load-carrying capacity, and maximum strain in the CFRP laminates, the response of the beams is compared to a strengthened unanchored beam and a beam anchored with

vertical anchors at each end. 2. Experimental program 2.1. Details of the tested beams

The experimental program consists of five RC beams. One beam is strengthened with CFRP laminates and is left unanchored. The rest of the four beams are strengthened and anchored with CFRP spike anchors. The spike anchors used herein had a diameter of 14 and 20 mm, inserted at either a 90º angle or 135º angle, respectively. The beams had a length of 2000 mm, a width of 200 mm, and a depth of 250 mm. The reinforcement consists of 2Ø12 rebars at the bottom and 2Ø8 at the top. The beams were designed to have adequate shear strength in order to induce a flexural failure. A schematic of the beams is shown in Fig. 1 and the strengthening and anchoring configuration are illustrated in Fig. 2. The test matrix with the anchors’ design parameters is explained in Table 1. Beams were tested under a four point bending test in a Universal Testing Machine (UTM) under a displacement-controlled rate of 2 mm/min. One linear variable differential transformer (LVDT) was placed under the beam’s soffit to measure midspan deflections.