INFLUENCE OF NON-METALLIC FIBRES ON THE SHEAR STRENGTH OF CONCRETE BEAMS REINFORCED WITH GFRP BARS

摘要

Concrete materials are typically characterized as brittle, with low tensile strength and straincapacity. However, with the use of fibres in concrete, this brittleness can be overcome, producingmaterials with improved strength, ductility and flexural toughness. This paper presents a structuralinvestigation that was carried out on the effect of non-metallic (synthetic) fibres on the shear behaviour ofconcrete beams reinforced with GFRP bars. Sixteen simply supported beams were prepared and tested.The beams were loaded with four point monotonic loading up to failure. The test variables were the fibrevolume, reinforcement ratio, depth of the beam and the shear span to depth ratio. The fibre volume ratioswere 0%, 0.5%, 0.75% and 1%. The test results were analysed and presented in terms of loaddeflection,failure patterns, cracking and ultimate loads. The test results revealed that the addition offibres enhanced the overall behaviour of the beams and their shear strength. The use of 1% fibrevolume ratio increased the beam ultimate load carrying capacity by 45% and increased maximum beamdeformation by 35%, when it is compared with similar beams with no fibres. In addition, the beams wereanalysed using a non-linear finite element model. Three dimensional solid elements were used to modelthe concrete. The predicted results from the FE analysis were compared with the experimental results.Good agreement was observed between the analysis and the experimental results in terms of theultimate load carrying capacity, load–deflection behaviour and mode of failure.1. IntroductionConventional steel reinforcement suffers from corrosion and this is exaggerated in cold climate regionwhere de-icing salts are used to remove snow from the road to maintain traffic. This leads to thedeterioration of concrete structures resulting in costly maintenance and repair which in turn shortens theanticipated service life of the structures. As an alternative to the traditional steel reinforcement, fibrereinforced polymer (FRP) materials have emerged as one of the most promising technologies in structuralengineering in the last decade due to their corrosion resistance, high strength to weight ratio, longerdurability and magnetic neutrality.The development of fibre-reinforced concrete began in the 1960s. Over the past 40 years, research wasconducted to understand the role of fibres in reinforced concrete elements. However, the research mostlycovered the effect of fibres in concrete elements with conventional steel as main reinforcement.Research results on using fibres in concrete with FRP bars as main reinforcement is rare.The shear strength of GFRP reinforced concrete beams is less than the conventional steel reinforcedconcrete beams (Michaluk et.al., 1998; Yost et. Al., 2001; Tureyen and Frosch, 2002). This can beattributed to the low modulus of elasticity of these bars. When these bars are used as main flexuralreinforcement in beams, they create wider cracks than conventional steel after cracking. Wider cracks