| Light-weight, durable bonded fibre reinforced plastics (FRPs) have been used extensively for the flexural strengthening (see below) of reinforced concrete beams but to a much lesser extent for shear strengthening. Yet in many reinforced concrete structures, strengthening against shear forces as well as bending moments is required. Most of the work to date on FRP shear reinforcing systems has primarily considered bonded passive reinforcement systems where unidirectional or two-dimensional FRP sheets, or laminated FRP sections are bonded to the surface of a beam. In these systems the reinforcement is passive and will not influence the shear behaviour until the concrete has cracked, or existing cracks widen further. A recent development has been the use of versatile unbonded prestressed FRP strap reinforcement. In this system, layers of thin carbon FRP (CFRP) thermoplastic tape are wound around a beam to form a strap which can be prestressed. The closed loop system does not need to be anchored in the concrete and the stressed strap provides active confinement to the concrete which will enhance the shear capacity of the beam.
One of the aims of the current research project is to compare the performance of bonded passive and unbonded prestressed FRP shear systems. Another goal is to investigate the influence of the load history on the strengthened behaviour since, in practice, structures requiring strengthening will have been subjected to a complex load history and may well be carrying significant dead loads while being strengthened.
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Testing of strengthened concrete T-beams - with prestressed CFRP shear straps (left) of bonded CFRP fabrics (right) |
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• Flexural strengthening 
• Column strengthening 
