Flexural Ductility Improvement of Frp-Reinforced Concrete Members

This dissertation, "Flexural Ductility Improvement of FRP-reinforced Concrete Members" by Tak-bun, Denvid, Lau, 劉特斌, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled Flexural Ductility Improvement of FRP-reinforced Concrete Members Submitted by LAU Tak Bun Denvid for the degree of Master of Philosophy at The University of Hong Kong in August 2006 Fiber-reinforced polymer (FRP) has become a practical alternative construction material for replacing conventional steel bars as reinforcement in concrete structures. Although recently guidelines for the design and construction of concrete reinforced with FRP bars are available, they are not comprehensive enough and some lack the support of experimental results. In addition, the testing method for determining the tensile strength of FRP bars still has room for improvement. One major problem in tensile tests of FRP bars is failure at the anchor or grip region. Existing guidelines about anchor protection of FRP bars are not practicable for most of tensile test machines. Therefore, theoretical and experimental analyses were carried out in this research to find a more suitable protection method for the anchor. Tensile tests were conducted on a large number of glass fiber-reinforced polymer (GFRP) bars having a range of diameters from 12 to 25mm. It was found that epoxy resin and aluminum are suitable materials for filler and anchor tube respectively. Finally, a more practicable and economical anchor design for FRP bars was proposed. Because FRP is a brittle material that has elastic behavior until failure, it greatly reduces the ductility of concrete members reinforced with FRP bars, which are referred to as FRPRC in this research. In order to improve the flexural ductility of an FRPRC i imember, and at the same time retain the high strength feature of its FRP bars, conventional steel longitudinal reinforcement is proposed to be added to form a hybrid FRPRC beam. To investigate the ductility improvement of hybrid FRPRC members, a number of beam specimens consisting of conventional steel-reinforced concrete (SRC) beams, pure FRPRC beams and hybrid FRPRC beams were fabricated and tested under three point monotonic loading. From the test results, it was evident that the hybrid FRPRC members behaved more ductile than the pure FRPRC beams, and the higher the degree of over-reinforcement (in terms of GFRP bars or both steel and GFRP bars), the more ductile the FRPRC beams. It is therefore concluded that the addition of conventional steel reinforcement could improvement the flexural ductility of FRPRC members, and over-reinforcement is a preferred approach in the design of FRPRC members to prevent brittle failure by fracture of FRP bars. In addition, to guarantee in the design that pure FRPRC sections are over-reinforced, it was proposed in this research that the over reinforcement ratio should be at least 40% larger than the balanced reinforcement ratio. The minimum content of FRP flexural reinforcement for strength was also investigated. Experimental results showed that the minimum FRP flexural reinforcement recommended by the existing guideline could be reduced by about 25%. As over-reinforcement is recommended in the design of FRPRC members, their failure is governed by concrete crushing in the compression zone. From the test results, it was found that stirrups with 135 hooks gave a better confinement for the compression zone, so that the ductility of FRPRC members could further be improved. ii ii DOI: 10.5353/th_b