Behaviour of rectangular RC columns confined with bi-directional GFRP under combined axial and bending loadings

Gora, Abdurra'uf Mukhtar (2022) Behaviour of rectangular RC columns confined with bi-directional GFRP under combined axial and bending loadings. PhD thesis, University of Nottingham.

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Concrete structural members, such as columns, can deteriorate owing to a variety of circumstances, including concrete cracks, steel reinforcement corrosion, poor structural design, excessive loading, natural disasters, and harsh weather conditions. Various corrective actions may be necessary to rehabilitate the structural members depending on the nature and severity of the deterioration or defect. Advanced fibre reinforced polymer (FRP) composites have been increasingly used over the last two decades for strengthening, upgrading, and restoring degraded civil engineering infrastructure. Substantial experimental investigations have been conducted in recent years to understand the compressive behaviour of FRP-confined concrete columns. It is very evident that only a few studies have investigated the behaviour of eccentrically loaded noncircular RC columns wrapped with FRP composites. This study presents the experimental investigation on the behaviour and performance of rectangular reinforced concrete (RC) columns with full bi-directional glass fibre reinforced polymer (GFRP) wrapping under combined axial and bending loading conditions.

To achieve the objectives of this research, small rectangular RC columns with a scale of 1:3 the prototype column's size and lower concrete compressive strength were used. A total of sixteen rectangular RC specimens with cross-sections of 100 × 150mm and 800mm in height were constructed and tested under axial, eccentric, and flexural loading conditions. The corners of columns were rounded with a radius of 20mm to prevent the FRP rupture failures. The effect of bi-directional GFRP reinforcement on rectangular RC columns with different number of layers (i.e. zero, one, two and three) and eccentricities (i.e. 0, 25mm, and 50mm) were investigated. Among the 16 rectangular RC specimens, 12 specimens were tested under axial and eccentric loading, and four specimens were tested under flexural loading condition. Moreover, a numerical study using finite element (FE) method was performed on 16 GFRP-confined rectangular RC specimens under concentric, eccentric and flexural loads, to determine the load-displacement behaviour and ductility.

The experimental results reveal that the rectangular RC columns with bi-directional GFRP confinement under axial loading achieved a substantial improvement in ultimate axial load capacity and ductility. Also, the ultimate axial capacity of GFRP confined rectangular columns increased with increasing number of bi-directional GFRP layers to a maximum of 187%. Similarly, the GFRP confined specimens under flexural loading achieved a significant enhancement in flexural load capacity of 51% in addition to ductility enhancement. Furthermore, subjecting the specimens to eccentric loading led to a loss in the ultimate capacity and ductility of the specimens. On the other hand, the loss in ultimate load carrying capacity and ductility increases with increased in eccentricity.

The results of finite element analysis (FEA) revealed a significant enhancement in the load carrying capacity and ductility of GFRP confined rectangular RC columns over the control columns (i.e. without GFRP wrapping). For columns governed by eccentric loading, the ductility significantly increases with increased in GFRP layers, and remarkably decreases when the eccentricity was increased. The comparison between the experimental and finite element analysis results of GFRP confined columns showed a reasonably close agreement, except in columns subjected to concentric loading. For specimens subjected to flexural loading, the FE results of the control beam agrees quite well with the load-deflection plot of the actual beam in both linear and nonlinear range, whereas the load-deflection curves of the FE GFRP wrapped beams are much stiffer than that of the experimental beams in both linear and nonlinear range of the curves.

The theoretical axial load-bending moment interaction diagram showed that specimens wrapped with three layers of GFRP reinforcement outperformed specimens with one and two layers of GFRP reinforcement. The axial load-bending moment interaction diagrams demonstrated that, with the exception of the control and three layers GFRP wrapped column, the FEA provided axial load values that were extremely close to the experimental values under concentric loading. When eccentric loading was applied, the FEA produced ultimate bending moment values that were higher than the experimental results. For specimens under flexural loading, the FEA gave bending moment values that were significantly greater than the experimental results.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Parvez, Mohammed Anwar
Jaganathan, Jayaprakash
Ali Mohamed, Abdullahi
Alengaram, U. Johnson
Keywords: bi-directional GFRP composite, concentric loading, ductility, eccentric loading, FRP confinement, rectangular RC section, reinforced concrete column
Subjects: Q Science > QD Chemistry
Faculties/Schools: University of Nottingham, Malaysia > Faculty of Science and Engineering — Engineering > Department of Civil Engineering
Item ID: 67463
Date Deposited: 27 Feb 2022 04:40
Last Modified: 08 Mar 2022 03:15

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