Serviceability and Ultimate Performance of Steel and Chopped Glass Fibre Reinforced Concrete Flexural Members: Experimental and Analytical Study

Abstract

Fibre reinforcement in concrete mitigates cracking, significantly enhancing peak, post-cracking, and toughness responses. The versatile applications of Fibre-reinforced Concrete (FRC) encompass parking lots, taxiways, runways, ground slabs, tunnels, barriers, railway tracks, site access road bridges, and culverts, showcasing its adaptability across diverse infrastructure projects, from transportation networks to structural foundations. A profound understanding of FRC's compressive and flexural behaviour holds paramount importance in designing structural elements such as beams, slabs, columns, piers, and compressive struts of beams. Commonly, Steel fibres (SFs) and glass fibres (GF) are often added to concrete to enhance toughness, durability, and post-cracking response, affecting the flexural and cracking behaviour of Fiber Reinforced Concrete (FRC). Understanding this is important because fibres increase moment resistance and stiffness. The investigation initiates with the optimization of mixture designs for FRC, examining the impact of fibre type (SF, GF, and/or a combination to evaluate the benefits of non-corrosive and deformable GF with higher stiffness SF), aspect ratios (55 for SF and 67 for GF), lengths (50 mm for SF and 36 mm for GF) and dosage (0.5, 1.0, and 1.5% by volume fraction). The findings reveal substantial reductions in slump with increased fibre content, offering nuanced insights crucial for concrete mixture designers and structural engineers. Moving to the compressive behaviour of FRC, the study examines the effects of incorporating SF and/or GF on critical parameters such as compressive strength, modulus of elasticity, Poisson’s ratio, and toughness index. A simplified model is proposed to understand how adding fibres changes the stress-strain relationship in concrete. Subsequently, the research delves into the flexural and cracking behaviour of FRC prisms, employing a combination of experimental and analytical methods. The outcomes introduce proposed design-oriented expressions for equivalent stress block parameters, refining our understanding of FRC's structural response. Addressing a notable gap in the literature, the thesis employs Finite Element Analysis (FEA) to model large-scale Steel Reinforced (SR)-FRC and Glass Fibre-Reinforced Polymer (GFRP)-FRC beams. This analysis extends beyond conventional load-displacement considerations to encompass parameters like crack width and reinforcement strain. The findings show the viability of FEA predictions for both steel and GFRP reinforced concrete beams response, indicating a potentially cost-effective alternative to extensive experimental programs. The recent update in one-way shear provisions for steel-reinforced concrete by the American Concrete Institute prompts consideration for similar provisions in Fibre-Reinforced Polymer (FRP) Reinforced Concrete (FRP-RC). The lower shear strength of FRP-RC, particularly GFRP, is attributed to its considerably lower modulus of elasticity compared to steel. This research evaluates existing design provisions for one-way shear in FRP-reinforced concrete, offering recommendations based on an analysis of 147 tests documented in the literature. The CSA S806-12 standard is considered the most consistent at predicting shear strength. Lastly, this study used the numerical database from FEA to develop service and ultimate design equations for FRC with SR and GFRP bars. The flexural and shear strength models demonstrated precision. Short-term deflection and reinforcement strain were obtained by deriving an effective moment of inertia for FRC. The FEA underestimates deflection because it often assumes ideal and perfect conditions. The analytical model accurately predicts reinforcement strain, aligning closely with FEA results. These findings significantly advance our understanding of FRC structures, guiding future research and practical applications in structural engineering. The investigation initiates with the optimization of mixture designs for FRC, examining the impact of fibre type (SF, GF, and/or a combination to evaluate the benefits of non-corrosive and deformable GF with higher stiffness SF), aspect ratios (55 for SF and 67 for GF), lengths (50 mm for SF and 36 mm for GF) and dosage (0.5, 1.0, and 1.5% by volume fraction). The findings reveal a reduction in slump with increased fibre content, offering nuanced insights crucial for concrete mixture designers and structural engineers. Moving to the compressive behaviour of FRC, the study examines the effects of incorporating SF and/or GF on critical parameters such as compressive strength, modulus of elasticity, Poisson’s ratio, and toughness index. A simplified model is proposed to understand how adding fibres changes the stress-strain relationship in concrete. Subsequently, the research delves into the flexural and cracking behaviour of FRC prisms, employing a combination of experimental and analytical methods. The outcomes introduce proposed design-oriented expressions for equivalent stress block parameters, refining our understanding of FRC's structural response. The thesis employs Finite Element Analysis (FEA) to model large-scale Steel Reinforced (SR)-FRC and Glass Fibre-Reinforced Polymer (GFRP)-FRC beams. This analysis extends beyond conventional load-displacement considerations to encompass parameters like crack width and reinforcement strain. The findings show the viability of FEA predictions for both steel and GFRP reinforced concrete beams response, indicating a potentially cost-effective alternative to extensive experimental programs. The recent update in one-way shear provisions for steel-reinforced concrete by the American Concrete Institute prompts consideration for similar provisions in Fibre-Reinforced Polymer (FRP) Reinforced Concrete (FRP-RC). This research evaluates existing design provisions for one-way shear in FRP-reinforced concrete, offering recommendations based on an analysis of 147 tests documented in the literature. The CSA S806-12 standard is considered the most consistent at predicting shear strength. Lastly, this study used the numerical database from FEA to develop service and ultimate design equations for FRC with SR and GFRP bars. The flexural and shear strength models demonstrated precision. Short-term deflection and reinforcement strain were obtained by deriving an effective moment of inertia for FRC. The FEA underestimates deflection because it often assumes ideal and perfect conditions. The analytical model accurately predicts reinforcement strain, aligning closely with FEA results. These findings significantly advance our understanding of FRC structures, guiding future research and practical applications in structural engineering.