PSI - Issue 54

Rami A. Hawileh et al. / Procedia Structural Integrity 54 (2024) 287–293 Hawileh et al./ Structural Integrity Procedia 00 (2019) 000 – 000

288

2

1. Introduction Strengthening and retrofitting of existing structures has proven to be an excellent solution for addressing the consequences resulting from various factors that contribute to the deterioration of structural members, including exposure to harsh environmental conditions, excessive loading due to changes in usage, and design or construction flaws (Danraka et al., (2017); Siddika et al., (2018)). Over the past four decades, the use of fiber reinforced polymers (FRP) as a strengthening system has gained widespread acceptance. This is primarily due to the superior benefits it offers compared to traditional methods such as steel plates, section enlargement, or concrete jacketing. The effectiveness of FRP as a strengthening system lies in its high strength-to-weight ratio, durability, non-obtrusiveness, and versatility (Assad et al., (2022); Choobbor et al., (2019); Hawileh et al., (2011); Mahmoud et al., (2021); M. Z. Naser et al., (2019)). FRP composites have proven successful in enhancing the properties of various structural components, including axial, flexural, and shear load capacities. However, a significant drawback of using externally bonded FRP laminates for strengthening systems is the premature debonding of the FRP from the concrete substrate, which hinders the attainment of the FRP composite's ultimate strength (Abdalla et al., (2020); Assad et al., (2022)). The prevention of debonding failure in RC strengthened beams has been extensively researched, with the anchorage of FRP laminates being a widely explored solution. Anchoring FRP laminates with spike anchors is proven to mitigate debonding failure and thus enhance the strength and deformability of strengthened beams (Ali et al., (2014); Al-Tamimi et al., (2011); Cortez Flores et al., (2020); Grelle et al., (2013); Llauradó et al., (2017); Mhanna et al., (2021); Naser et al., (2012); Ozbakkaloglu et al., (2009); Shekarchi et al., (2020); Sun et al., (2016)). By delaying the occurrence of debonding, the utilization of FRP is enhanced, leading to improved performance in RC beams. The primary role of the anchorage system is to facilitate the transfer of stresses between the FRP laminate and the concrete substrate, effectively arresting the propagation of cracks (Smith et al., (2002a), (2002b); Teng et al., (2003)). Another advantage of FRP dowel anchors is their versatility in accommodating different structural configurations. The straight anchor configuration is commonly used in structural joints, such as beam-to-slab, slab-to-wall, and wall-to-wall connections, where direct tension is the primary load. On the other hand, bent anchors are utilized for anchoring FRP laminates in strengthened beams or slabs, where both tension and shear forces are present. This flexibility allows for tailored solutions based on the specific requirements of the structure. Furthermore, FRP dowel anchors offer corrosion resistance, as FRP materials are non-metallic and do not corrode like traditional steel reinforcement. This feature ensures the long-term durability and service life of the strengthened structure, particularly in harsh environments or in structures exposed to aggressive chemicals. Numerous studies have demonstrated the effectiveness of anchoring FRP laminates in delaying or preventing brittle failure, specifically debonding, in externally bonded strengthened beams. However, most of the available data and models on FRP anchors in the literature were obtained from testing small anchors, i.e., anchors with small dimensions, under direct pullout or pull-off shear tests. Ozbakkaloglu et al. (2009) inspected the effect of anchor configuration on the behavior of FRP plates externally bonded to concrete members through single shear pull-off tests. Authors tested 33 specimens of 350 mm length, 150 mm height, and 25 mm width. The anchors configuration varied as single, double, or multiple anchors in the longitudinal or transverse direction. Their results indicated that peak loads and ductility increase with the increase in anchors numbers. Limited number of studies were conducted on FRP anchors in combination with externally bonded reinforcement (EBR) systems using bending tests on anchored beams. Zaki et al. (2019) tested three full scale T-beams and another three rectangular beams under four-point bending test. Each tested group of beams included a control specimen, and the rest are strengthened with CFRP sheets and anchored along the shear span using either U-wraps or FRP anchors. The diameters of the FRP anchors were 16 and 19 mm. As a result, authors proposed a multiplier coefficient for the ACI440.2R-17 (2017) equation of debonding strain. This multiplier accounts for the development in strain due to the sheets anchorage and was calculated by dividing the load at experimental failure by the predicted load at FRP debonding strain. The highest multiplier value corresponded to the T-beam having 16 mm diameter anchors and it was 1.66. Sun et al. (2016), (2018) conducted 21 three-point bending tests on concrete prisms of (152×152×610) mm dimensions under three-point bending test. They proposed a new anchoring technique which showed an improved behavior in terms of utilization of EB FRP sheets. They also noticed that reducing the fanning angle prevents the unfavorable failure of anchor-sheet delamination and anchor rupture. In another study published by Sun et al. (2020), they used the experimental results from 64 tests on anchors that failed in rupture to evaluate the anchor strength using