The comparative performance and behaviour of concrete elements containing glass-fibre reinforced plastic reinforcing bars

• Main Author: Ulas, Esref M.
• Published: Sheffield Hallam University 2001
• Subjects: 333.7
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.741345

Corrosion of steel reinforcement is a major concern in concrete construction, particularly in aggressive environments. Therefore corrosion resistant materials such as fibre composites are becoming increasingly feasible as an alternative concrete reinforcement. There are relatively few reported design guidelines for fibre composites in concrete. Hence, there is an urgent need for research and development to extend existing guidelines and standards such as those produced by the UK Institution of Structural Engineers and the ACI Committee (US), to encourage the wider use and acceptance of fibre composites as an alternative to steel in reinforced concrete elements. This investigation compares the behaviour and properties of a range of reinforced concrete beams under two point loading comprising different concrete grades and types using both steel and Glass Fibre Reinforced Plastic (GFRP) as primary and secondary reinforcement. A variety of conventional and 'novel' rebar configurations were used to assess their effect upon material efficiency and load capacity. Compressive and tensile strength and elastic moduli of all component properties were measured together with load, deflection, rebar and concrete strains on the reinforced concrete beams. Health and safety concepts through a risk assessment process were introduced for the testing at an early stage of the investigation. Principal measures of beam performance include the ultimate load capacity, stiffness and failure modes together with a 'performance quotient'; a mathematical expression derived as an efficiency comparator for beams of different types and composition. Photographic and video records were also used to monitor behaviour throughout. Experimental measurements generally showed good agreement with the corresponding theoretical, quasi-theoretical and design based values although the latter tended to overestimate the structural performance of the beams. In general, load capacity increased with increase in main rebar area but was affected to a lesser extent by concrete strength. The beams reinforced with steel had a greater load capacity than those reinforced with GFRP. However, GFRP reinforced beams generally displayed a greater capacity to absorb energy than steel but exhibited reduced stiffness at any given load although this was enhanced by the inclusion of glass fibres in the mix. Cracks in the GFRP reinforced beams were usually larger and deeper compared with those in the equivalent steel reinforced beams. Failure of the more lightly reinforced steel beams, including one GFRP beam, were predominantly in 'flexure'. The more heavily reinforced steel and the remainder of the GFRP reinforced beams exhibited mostly 'shear-bond' type failure. The 'novel' rebar geometry proved to be a simple, efficient and viable alternative to conventional rebar configurations in terms of load capacity and preferred mode of failure. It is suggested that further developments and applications could focus on small reinforced concrete elements such as lintels in aggressive environments and further refinement of the 'performance quotient' concept.