Doctor of Philosophy
School of Civil, Mining and Environmental Engineering
Hasan, Hayder Alaa, Structural Behaviour of Circular High Strength Concrete (HSC) Columns Reinforced with Glass Fibre-Reinforced Polymer (GFRP) Bars and Helices under Different Loading Conditions, Doctor of Philosophy thesis, School of Civil, Mining and Environmental Engineering, University of Wollongong, 2018. https://ro.uow.edu.au/theses1/291
Steel reinforcement in reinforced concrete structures is vulnerable to corrosion, especially in marine structures or structures located in aggressive areas or moist environments. The corrosion of the steel reinforcement causes huge maintenance cost and in some situations leads to severe damages in the concrete structures.
Fibre Reinforced-Polymer (FRP) bars have several advantageous properties, including, light weight, high tensile strength, and electromagnetic neutrality, in addition to the corrosion resistance. The FRP bars became ideal replacements for the conventional steel bars in reinforcing concrete structures that require such characteristics. However, FRP bars are not recommended to reinforce concrete columns. This is because of the anisotropic and nonhomogeneous nature of the FRP bars, which lead to micro-buckling in the internal fibres of the FRP bars when subjected to axial compression.
The majority of the previous research studies on FRP bar reinforced concrete columns are limited to columns constructed with normal strength concrete (NSC). Although high strength concrete (HSC) columns offer several advantages over NSC columns such as enhanced durability and considerable cost saving resulting from the reduction of member size, only a few research studies investigated the behaviour of FRP bar reinforced HSC columns. The observations obtained from the studies on FRP bar reinforced NSC columns might not be applicable for FRP bar reinforced HSC columns since the behaviour of HSC columns is fundamentally different from the behaviour of NSC columns. Given the lack of experimental research studies on HSC columns reinforced with FRP bars, this study aims to investigate the structural behaviour of Glass-FRP (GFRP) bar reinforced circular HSC columns under concentric and eccentric axial loads and under four-point bending.
The other focus of this study is to investigate the structural behaviour of GFRP bar reinforced steel fibre high strength concrete (SFHSC) columns. The main objective of using steel fibres is to overcome the lack of ductility that might be experienced by the GFRP bar reinforced HSC columns since both HSC and GFRP bars are brittle materials compared to NSC and steel bars, respectively.
In this study, a total of 20 circular steel and GFRP bar reinforced HSC and SFHSC column specimens were experimentally tested. The column specimens were 210 mm in diameter and 800 mm in height. Critical assessment on the effect of the concrete compressive strength, loading conditions (concentric and eccentric axial loads and fourpoint bending), type of reinforcement (steel and GFRP), the GFRP transverse reinforcement ratio and the inclusion of steel fibres on the performance of GFRP bar reinforced HSC columns was made. In addition, analytical approaches were developed to predict and to examine the axial load-bending moment (𝑃 − 𝑀) interaction diagrams and the moment-curvature (𝑀 − ∅) relationships of the GFRP bar reinforced HSC and SFHSC column specimens. Reasonable correlations between the experimental and the analytical results were obtained.
The experimental and the analytical results reveal that GFRP bars can be used as longitudinal reinforcements to enhance the performance of concrete columns under axial and flexural loads. In addition, neglecting the contribution of the longitudinal GFRP bars may lead to overly conservative estimations for the maximum axial load carrying capacity of GFRP bar reinforced concrete columns. Finally, the ductility and post-peak axial load-axial deformation behaviour of the GFRP bar reinforced HSC specimens can be significantly improved by adding steel fibres and using closely spaced GFRP helices.
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