2.0 REVIEW OF LITERATURE. In the last few years, the use of fiber-reinforced plastic (FRP) rebars to replace steel

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1 REVIEW OF LITERATURE 2.1 General In the last few years, the use of fiber-reinforced plastic (FRP) rebars to replace steel rebars has emerged as one of the many techniques put forward to enhance the corrosion resistance of reinforced concrete structures. In particular, FRP rebars offer great potential for use in reinforced concrete construction under conditions in which conventional steelreinforced concrete has yielded unacceptable service. If correctly applied in the infrastructure area, FRP composites can result in significant benefits related to both overall cost and durability. Other advantages include high strength- and stiffness-toweight ratios, resistance to corrosion and chemical attack, controllable thermal expansion and damping characteristics, and electromagnetic neutrality. These advantages could lead to increased safety and provide savings in fabrication, equipment, and maintenance costs. The most commonly used FRPs for civil engineering applications are carbon (CFRP), aramid (AFRP), and glass (GFRP). They are utilized as reinforcement for reinforced and prestressed concrete members, ground anchors, and for repairing or strengthening existing concrete structures. 2.2 Application for FRP reinforcement The use of GFRP bars for reinforcing concrete bridge decks has captured some interest, particularly for the case of the replacement of the top steel mat. The idea is to eliminate one of the major causes of deterioration (i.e., the steel reinforcement embedded in the concrete region more exposed to chlorides) without significantly increasing cost of construction and without totally removing steel reinforcement. In underground applications, FRP bars have historically been used as temporary soil anchors and,

2 15 recently, have become the reinforcement of preference in ground containment walls for tunneling projects. In such projects, the main purpose of a concrete wall of which the soft-eye is part is to contain the ground allowing both the entrance and removal of the Tunnel Boring Machine (TBM). By using concrete reinforced with GFRP bars in the soft-eye region, the cutting operations are simplified due to the low transversal resistance of GFRP materials compared to steel. Another interesting field of application that has become very common is the use of FRP reinforcement for the RC elements that constitute the containment unit of Magnetic Resonance Imaging (MRI) equipment in hospitals. In this instance, FRP reinforcement is used in lieu of steel for its magnetic transparency. In general carbon fibres are considered to have a very good durability in alkaline environments (as well as acid environments), and research has shown that for CFRP normally only small reductions in tensile strength can be found after accelerated exposures. Glass fibres, on the other hand (and consequently GFRP), are known to be susceptible to degradation due to base hydrolysis. The E-glass fibre, which is the most commonly used glass fibre type for GFRP reinforcement, is known to be susceptible to attack by OH-ions when in contact with an base liquid. Hence, an important task for the matrix is to act as a barrier, protecting the glass fibres from harmful agents. However water and possibly alkalis will penetrate through micro cracks or even the un-cracked resin matrix and eventually attack the fibres, the fibre/matrix interface or the matrix itself. Nevertheless, being considerably cheaper than CFRP, GFRP is still an interesting material for concrete reinforcement.

3 Literature review Amir Mirmiran et al. (2001) were tested seven numbers of concrete filled fibre reinforced polymer tubes to study the slenderness limit for hybrid FRP- concrete columns and developed an analytical tool with an incremental approach. They also conducted the parametric study and concluded that, because of higher strength and lower stiffness than steel, hybrid FRP- concrete columns more susceptible to slenderness effects. Amir Mirmiran et al (2001) carried out a detailed parametric study by varying the type of reinforcement and recommends reduction of slenderness limit from 22 to 17 for GFRP reinforced column bent in single curvature. Mohamed Saafi (2002) carried out a study to obtain the effect of concrete cover, fire exposure time on FRP members, shear and flexural capacities of reinforced beams and recommended 64 mm as minimum concrete cover for fire resistance. Deitz et al (2003) studied GFRP reinforced compression members with 45 samples to determine the ultimate strength and Young s modulus and found that, the ultimate compressive strength is equal to 50% of ultimate tensile strength. Camione and Miraglia (2003) examine the analytical compressive behaviour of concrete members reinforced with Fibre reinforced polymer. They also studied the bearing capacity and maximum strain for the members with circular, square and square with round corners and concluded that, the model proposed in the study allows one to evaluate ultimate strain concrete core based on a simplified energetic approach. Kadioglu and Pidaparti (2005) studied the effect composite rebar s shape in reinforced concrete beam type structures through finite element analysis. They analysed various

4 17 configurations of composite rebar and concluded that, circular rebar with 6 square ribs with 1 offset offer best configuration under axial and torsional loadings. Ching Chiaw Choo et al (2006) presented ultimate strength approach to examine the strength interaction behaviour of FRP concrete columns and also slenderness effects using numerical integration technique. It was concluded that, the columns exhibit increased resistance at low axial load levels. Darren Eddie et al (2001) studied the possibilities for the use of GFRP rebar in the concrete pavements especially in corrosive environments and subjected to static and cyclic loads and concluded that the load transfer efficiencies of GFRP are acceptable. Ehab El-Salakawy et al (2003) investigated the use of GFRP rebar in concrete bridge barriers under static and dynamic loads and concluded that the behaviour is very similar to the concrete bridge barriers with steel bars in terms of cracking. Michael R. Wisnom and Jiirgen Hiiberle (1994) investigated the buckling response of 2 mm thick struts of length 20, 30 and 50 mm with approximately built-in end conditions. Good correlation was obtained with the results of large displacement finite element analysis taking into account non-linear material behaviour and found that 50 mm struts buckled stably and then failed due to interlaminar shear, where as 20 and 30 mm struts failed due to a catastrophic instability after the onset of buckling. They concluded that, for all three lengths, ultimate failure was not controlled by the material compressive strength and for the shorter struts which fail at relatively high stresses, it is essential to take account of the nonlinear material behaviour in the fibre direction, and also in shear.

5 18 O. Chaallal and B. Benmokrane (1996) reported the results of a laboratory investigation of a glass-fiber plastic rod used as a rebar for concrete structures. It includes three parts: (a) characterization of the rod, (b) bond performance of the rebar, and (c) flexural behaviour of concrete beams reinforced with such a rebar. It was found that the glass fiber rod is very light and behaves elastically up to failure. It possesses a high ultimate tensile strength, but a low ultimate strain and modulus of elasticity. Also its coefficient of thermal expansion is similar to that of concrete. They found that, the beams reinforced with glass-fiber rebars behaved satisfactorily in comparison to identical beams reinforced with conventional steel rebars, although they featured more cracking, particularly at moderate to high loading. Roman Okelo and Robert Yuan (2005) focused on the bond strength of fiber reinforced polymer rebars in normal strength concrete. Four different types of rebars were tested using the pullout method: AFRP, CFRP, GFRP!, and steel. This involved a total of 151 specimens containing 6, 8, 10, 16, and 19 mm rebars embedded in a 203 mm concrete cube. The test embedment lengths were five, seven, and nine times the rebar diameter. For each rebar, the test results include the bond stress slip response and the mode of failure. The test results showed that the bond strength of an FRP rebar is, on average, % the bond strength on a steel rebar for pullout failure mode. Based on this research, a proposal for the average bond strength of straight FRP rebars in normal strength concrete is made, which verifies an existing bond strength relationship with GFRP and extends its application to AFRP and CFRP. It is an expression that is a function of the rebar diameter, and the concrete compressive strength.

6 19 Grira and Saatcioglu (2000) designed, constructed and tested full size columns confined by CFRP grids. The columns were reinforced with steel bars as longitudinal reinforcement and CFRP as transverse reinforcement. The columns were tested under stimulated seismic loading and exhibited ductile response when properly confined by the grids. The experimental investigations indicated that FRP could be used as column confinement reinforcement for improved seismic performance. Wu (1990) reported that the compressive strength of FRP was lower than its tensile strength. Accordingly, the compressive strength of GFRP, CFRP and AFRP bars were 55%, 78% and 20% of their tensile strengths. Paramanantham and Daniali (1993) investigated the behaviour of FRP reinforced concrete columns under concentric and eccentric loading, by testing small-scale specimens. It was concluded that the concentric capacity of specimens was very similar to each other. The FRP bars were able to contribute to the load carrying capacity by developing stresses corresponding to strains. Alsayed et al (1999) performed a comparative study between steel and FRP reinforced concrete columns and tested a total of 15 columns with different combinations of steel and GFRP reinforcement, including all GFPR reinforced columns. The results indicated that, FRP reinforcement resulted in approximately 10% reduction in concentric colun capacity as compared to steel reinforcement.

7 Objectives of the present research work Based on the critical review of literature, the following objectives are considered for the present study. To study the strength characteristics of High Performance Concrete columns with GFRP reinforcement under axial loading To study the effect of variation of slenderness ratio on strength characteristics of the column To study the effect of variation of percentage of reinforcement on strength characteristics of the column To compare the characteristics of HPC columns with GFRP reinforcement and conventional steel reinforcement on load carrying capacity and load-deformation characteristics To validate the experimental results of load deformation characteristics with the results of analytical model