A Ductile Hybrid Fiber Reinforced Polymer Tendon For Civil Engineering Applications

Fiber-reinforced polymer (FRP) composites have become competitive structural materials for civil engineering applications because of their superior advantages such as a high strength-to-weight ratio, corrosion resistance, a wide range of working temperatures, and the ease of handling and construction. FRP has been used for reinforcing/strengthening of new/existing reinforced concrete structures. However, the application of FRPs in structures cannot satisfy all of the structural integrity requirements. For instance, in the case of FRP with high strength and high elastic modulus, such as carbon FRP, the desired ductility of the structure is difficult to achieve. This is attributable to the inherently small failure strain of carbon FRP. Additionally, carbon FRP is also much more expensive than other types of FRP. In contrast, the relatively inexpensive FRPs, such as glass FRP with larger failure strain, can make structures more ductile; however, their relatively low modulus and poor creep behavior usually restricts their application because of structural deformation requirements.Bridge deck slabs are one of the most corrosion-vulnerable bridge components due to the direct exposure to de-icing chemicals and severe weathering conditions. The use of fiber-reinforced polymer (FRP) as reinforcement for bridge deck slabs is a promising solution to corrosion-related problems. Recently, glass FRP (GFRP) bars have been widely used as internal reinforcement for concrete bridge deck slabs since they are less expensive compared to the other kinds of FRPs (Carbon and Aramid). However, because of the relatively low stiffness of GFRP composites, RC-members reinforced with GFRP will have larger deflections and crack widths than steel reinforced members. Consequently, serviceability requirements govern the design of FRP-RC members. In such circumstance, previous studies on FRP-RC deck slabs concluded that to achieve the satisfactory of serviceability, FRP reinforced concrete bridge decks should sustain the same reinforcement stiffness as those bridge decks reinforced with the conventional steel reinforcement. However, the experiments of deck slabs tested in literature, revealed that the failure of deck in punching shear exhibited the carrying capacities of more than three times the factored design. Those results reflect the high material waste in the design of the FRP-RC bridge decks.To overcome the aforementioned limitations and to enhance the utilization of various FRP composites, this thesis, introduces two levels of study incorporating advanced FRP composites in the design:performance of hybrid FRP tendons and an iterative analytical model to predict its properties were studied first; and then the hybrid FRP tendons were used to prestress FRP-RC bridge deck slabs in order to eliminate the material waste.Firstly, this thesis presents the hybridization of different types of fibers to overcome their shortcomings, to integrate their advantages, and to subsequently achieve the best performance-to-price ratio. In addition, through hybridization, the mechanical properties of the FRP composites can be tailored for specific applications. The behavior of hybrid FRP tendons was studied experimentally and analytically. Then, the behavior of partially prestressed FRP-RC deck slabs with the developed hybrid FRP tendons was experimentally investigated. Finally, numerical study on the prestressed FRP-RC bridge deck slab was conducted; the numerical study examines the macro and micro behavior of concrete bridge deck slabs reinforced with partially prestressed fiber reinforced polymers (FRP) bars under the effect of a concentrated load of a vehicle-wheel. Finally, a comprehensive parametric study was conducted.The thesis consists of six chapters. The introduction of the study and the literature review are given in Chapter 1. State-of-the-art of the hybrid FRP composites, FRP-RC bridge deck slabs and FPR grids were included in the literature review. Chapter 2 presents a new methodology for predicting the tensile behavior of hybrid FRP tendons by considering the interfacial stress transfer between the resin and the fibers in hybrid FRP. Subsequently, the authors utilize the fundamental concepts of fracture mechanics to derive a model capable of predicting the mechanical properties of hybrid FRPs. In Chapter 3, the author conducted an experimental study on the tensile properties of hybrid basalt/carbon FRP tendons and hybrid glass/carbon FRP tendons. They identified the effects of resin type, fiber fraction, and fiber arrangement over the cross section. Chapter 4 investigates the behavior of full-scale deck slabs transversely reinforced and prestressed with basalt/carbon FRP hybrid tendons. The study aims to eliminate the FRP reinforcement amount for FRP-RC bridge deck slabs. A total of seven square slabs, with 2400 mm side length and 200 mm thickness were constructed and tested. Two non-prestressed deck slabs, steel-RC deck slab and FRP-RC deck slab, were designed according to the Canadian highway bridge design code CSA-S6-06 and served as control slabs. Three main variables, namely, FRP-reduction factor, prestress level, and partial prestressing index were investigated. Chapter 5 includes numerical study on behavior of partially prestressed FRP-RC bridge deck slabs. The aim of this chapter is to examine numerically the macro and micro behavior of concrete bridge deck slabs reinforced with partially prestressed fiber reinforced polymers (FRP) bars under the effect of a concentrated load of a vehicle-wheel. The numerical simulation is based on previously tested seven FRP reinforced concrete full scale bridge deck slabs. Finite element (FE) analyses and findings of reinforced concrete slabs subjected to punching load is evaluated and compared with the experiment results. Based on the created model, parametric study on RC bridge deck slabs reinforced and prestressed with FRP tendons were also performed. The following key conclusions were reached based on the aforementioned studies:a) the proposed model accurately identified the load drop at the LE fiber rupture, the failure load, and the failure strain of hybrid FRP composites; b) based on the experimental study on a series of hybrid FRP tendons, this study presented a new ductile basalt/carbon FRP hybrid tendon, with a failure strain of 3.61%, which was approximately 105% higher than its pseudo-yielding strain, and a failure load that was 1.35 times its pseudo-yielding load; c) Through proper design of the FRP-prestressed slabs, FRP-reduction facto of 0.45, cracking load of 73% higher than the FRP-RC control slab, and failure load of 2.6 the design factored load could be achieved; d) It has been shown that the load versus deflection diagram, reinforcement strains and ultimate load capacity obtained from FE analyses, with a reasonable degree, match with the experimental results. The detailed concluding remarks of this thesis are summarized in Chapter 6. Some research significance and future recommendations are also included.