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Fibre Reinforced Plastics (FRP)

FRP reinforcement consists of high strength/high stiffness fibres combined with a suitable resin to form a rod or grid. The most commonly used fibre is glass, combined with a vinylester resin, although carbon/epoxy products are available. Glass FRP rods have ultimate strengths in the region of 1200N/mm2 and a stiffness of about 40kN/mm2.

Carbon FRP rods have higher stiffnesses. Because FRP materials are brittle (i.e. they do not yield) modified design approaches are required. Guidance has been published by the Institution of Structural Engineers. FRP reinforcement cannot be bent on site to form links etc. Bent shapes must be specially prepared by the manufacturer.

FRP reinforcement has been used in many applications, such as bridge decks. They have been used under sensitive electronic equipment where stray electrical currents would be a problem. In Japan, FRP grids have been used to reinforce sprayed linings for tunnels. It should be noted that FRP reinforcing bars of a given size are likely to be at least twice the cost of carbon steel bars of the same size.

FIB (Federation internationale du beton) Bulletin 40, FRP reinforcement in RC structures, summarises the main physical and mechanical properties of FRP reinforcing bars, with special emphasis on durability aspects. For each of the typical ultimate and serviceability limit states, the basic mechanical model is given, followed by different design models according to existing codes or design guidelines. However, the Bulletin does not propose any final set of design formulae; the Task Group that prepared the document is continuing to refine the models used, which may eventually lead to a completely new design philosophy, different from that for conventional steel reinforcement.

Acknowledgement: The Concrete Society

Other references:
FIB (Federation internationale du beton), ´FRP reinforcement in RC structures´, Bulletin 40, 2007.

J L Clarke (Editor), ´Alternative materials for the reinforcement and prestressing of concrete´, Chapman & Hall, 1993.

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Interim guidance on the design of reinforced concrete structures using fibre composite reinforcement