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Concrete In Australia : June 2014
Concrete in Australia Vol 40 No 2 47 repair and maintenance due to steel corrosion (Achillides & Pilakoutas, 2004) will be avoided. However, the use of FRP bars as reinforcement in concrete structures is still unfamiliar to many practising Australian engineers even though there are full material and design codes in Canada (2008) and America which they can follow to design with FRP, and the BCA allows this under the alternative provision. Garnaut4 indicated that builders may avoid adopting products based on new technology if they cannot assess their reliability and use more familiar, older and less efficient products. In order to encourage its development and use, a better understanding on the behaviour of concrete structures reinforced with FRP bars should be gained to ensure confidence in the design and utilisation of this new technology as adopted widely in North America for many years. For example, Pultrall the manufacturer of V-Rod, has built more than 350 major highway bridge decks using V-Rod, along with water retaining structures, underground suspended car park slabs and electrical applications, as FRP is nonferrous and will not conduct electricity. The impressive list goes on. This paper provides an overview on the current research, development and application of FRP bars as internal reinforcement in concrete structures to ensure that Australia is properly informed in the engineering research for this advanced material allowing its responsible introduction and wider use. Furthermore, information on international codes and standards on FRP bars are briefly discussed for Australian engineers to familiarise themselves with designing and effectively utilising this material in civil infrastructure. Figure 2: The V-Rod GFRP bars. Table 1: Guaranteed properties of V-Rod GFRP bars. Bar diameter Nominal cross- sectional area (mm2) Guaranteed tensile strength (MPa) Modulus of Elasticity (GPa) Ultimate elongation (%) 12.7 mm 129 1312 65.6 + 2.5 2.00 15.9 mm 199 1184 62.6 + 2.5 1.89 19.0 mm 284 1105 63.7 + 2.5 1.71 2.0 GFRP BARS AS INTERNAL REINFORCEMENT TO CONCRETE STRUCTURES The extensive research and development efforts at the University of Sherbrooke in Canada have contributed to the increasing application of the FRP bars as internal reinforcement in concrete structures. The University of Sherbrooke is one of the key member universities of the Intelligent Sensing for Innovative Structures (ISIS Canada), which is a collaborative and research process established to accelerate the transfer of the technology from the laboratory to the marketplace. This section presents some of the current research and development activities at the University of Sherbrooke on the behaviour of concrete structures reinforced with GFRP bars. 2.1 GFRP bars and properties V-Rod, produced by Pultrall in Canada, is one of the most commonly used commercially available FRP reinforcing bars. This reinforcement bar (Figure 2) is made up of fibres which provides the mechanical strength as well as resin which acts as the matrix and increases the chemical resistance of the product. The glass fibre reinforced polymer (GFRP) bars were manufactured by a pultrusion process of continuous longitudinal E-glass fibres impregnated in modified vinyl ester resin. The surface of the bar was coated with Grade 24 silica sand to promote the bonding between the concrete and the reinforcement. The fibre content of these FRP bars is almost 85% by weight and its mechanical properties as reported by the manufacturer are presented in Table 1. As previously mentioned, hundreds of major projects have been completed internationally as well as in Australia with this material, some of which are presented in the latter part of this paper. 2.2 FRP rebar as reinforcement in beams GFRP bars are a competitive option as reinforcement in concrete beams. Benmokrane et al (1995) conducted an experimental and theoretical comparison between flexural behaviour of concrete beams reinforced with FRP reinforcing bars and deformed steel bars. Comparisons were made in relation to cracking behaviour, load-carrying capacities and modes of failure, load-deflection response, flexural rigidity, and strain distribution. The results revealed that a perfect bond exists between FRP reinforcing bars and the surrounding concrete. The crack pattern and spacing in concrete beams with FRP bars were similar to those of steel reinforced concrete beams at low load. However, there were more and wider cracks at the service load. Moreover, the results of the beam tests indicated that the ultimate strength of GFRP 46-56 - Manalo.indd 47 46-56 - Manalo.indd 47 22/05/14 11:56 AM 22/05/14 11:56 AM