Four large scale concrete beams of 4.2 m length and 200 × 400 mm cross-section were built and tested under four-point bending. Two beams were used as control beams and were reinforced with mild steel for both shear and flexure. The flexural and shear reinforcement for the remaining two beams were provided by externally bonded carbon fibre (CFRP) sheet. In addition, to achieve ductility in the CFRP reinforced beams, a low modulus high strain high density polypropylene grid (HDPP) was placed within them. The primary focus of this study was to achieve ductility via the provision of HDPP but it was also intended to prevent delamination of bonded CFRP sheets by attaching some of the laminae to the sides of the beam rather than attaching them all to the beam soffit. Finally, the magnitude of shear that could be resisted by externally bonded CFRP U stirrups was investigated. The hybrid reinforced beams achieved their design capacity and initial failure occurred due to rupture of CFRP sheet in the maximum moment region, followed by some delamination. The CFRP stirrups reached 70% of their ultimate strain capacity. After the rupture of CFRP, the HDPP provided the beams with residual strength, but due to the low modulus of HDPP, the deformations of the beams increased substantially.
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