This thesis consists of several experimental and analytical studies. Each individual study comprising this thesis has been published or submitted for publication as journal articles throughout the period of the Ph.D. study, but these studies are presented in this thesis as chapters in a consistent and cohesive format. This thesis is structured into nine chapters. A brief summary of each individual chapter contained in this thesis is outlined as follow:
Chapter One defines the current gap in the existing research literature regarding the use of GFRP bars in reinforcing circular high strength concrete columns. Chapter One also defines the main objectives of this research study and the methodologies adopted to achieve these objectives. The layout of the thesis is also presented in Chapter One.
Chapter Two presents the mechanical properties (compressive strength, flexural strength and splitting tensile strength) of the HSC and the SFHSC used in constructing the specimens of Series 1, Series 2 and Series 3 as defined in the Methodology Section above. In addition, Chapter Two presents a new method of testing concrete under uniaxial tension [20]. The method was developed to overcome the difficulties associated with the direct tensile testing methods of concrete adopted in the previous research studies. The feasibility of using the developed method in testing concrete samples under uniaxial tension was assessed through testing different types of concrete.
Chapter Three presents experimental and analytical investigations on the effect of reinforcement type (Steel and GFRP), the pitch of the transverse helices and the loading condition (concentric and eccentric axial loads and four-point bending) on the behaviour of circular high strength concrete columns [21].
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Chapter Four presents a comprehensive experimental and analytical comparison between the structural behaviour of circular normal strength concrete and high strength concrete columns reinforced longitudinally with GFRP bars and confined with GFRP helices under axial and flexural loads [22].
Chapter Five presents the results of experimental and analytical investigations on the effect of steel fibres on the failure modes, maximum axial load carrying capacity, post- peak axial load-axial deformation behaviour and the ductility of GFRP bar reinforced circular high strength concrete columns [23].
Chapter Six reviewed the equations proposed in the previous research studies to predict the axial load carrying capacity of FRP bar reinforced concrete columns [24]. Also, Chapter Six presents an explanation on the different concepts adopted in these equations to predict the contribution of the FRP longitudinal reinforcing bars in the total axial load carrying capacity of FRP bar reinforced concrete columns. Furthermore, based on the experimental results of FRP bar reinforced concrete columns reported in this study and in other studies available in the literature, a new equation for predicting the maximum axial load carrying capacity of NSC and HSC columns reinforced with different types of FRP bars was proposed and critically assessed in Chapter Six.
Chapter Seven and Chapter Eight clarify developed analytical approaches for conducting the axial load-bending moment interaction diagrams (𝑃 − 𝑀) and the moment-curvature relationships (𝑀 − ∅) for GFRP bar reinforced circular concrete columns [25-26]. The stress-strain constitutive models of confined; unconfined concrete and GFRP reinforcement, in addition to the analytical considerations pertaining to the analysis are also presented in these chapters. The analytical results presented in Chapter Seven and Chapter Eight were verified with experimental results of the column specimens tested in this study and other column specimens taken from available literature. Parametric studies were also conducted in these chapters to investigate the effects of different parameters (i.e. concrete compressive strength, longitudinal and transverse GFRP reinforcement ratios and the slenderness ratio of the columns) on the axial and flexural response of GFRP bar reinforced circular NSC and HSC columns.
Chapter Nine provides a summary of this research study and the overall conclusions based on the experimental and analytical investigations conducted in this research study. In addition, Chapter Nine provides recommendations for further research studies.
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References
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[21] Hadi, M. N. S., Hasan, H. A., and Sheikh, M. N., (2017), “Experimental investigations of circular high strength concrete columns reinforced with Glass Fiber-Reinforced Polymer bars and helices under different loading conditions,” Journal of Composites for Construction, Vol. 21, No. 4, 04017005 pp.
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RT = reinforcement type (steel or GFRP) 𝑓𝑐′ = compressive strength of concrete
MP = mechanical properties of GFRP bars 𝜌𝑓 = GFRP longitudinal reinforcement ratio
𝑣𝑓 (%) = steel fibre content
𝑓1⁄𝑓𝑐𝑜 = GFRP transverse reinforcement ratio (confinement ratio)
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