The technique of strengthening existing reinforced concrete structures with Carbon Fibre-Reinforced Plastics (CFRP) has become more and more popular over the last couple of decades. Although lots of research efforts have been put on the flexural strengthening with CFRP laminates, most investigations have focused on simply supported beams under 3-point or 4-point bending. These loading conditions, however, may not represent the real situation in practice. In order to have a better understanding of the failure behaviour under practical situations, the present work focuses on CFRP-strengthened beams (i) under quasi-distributed loading , and (ii) with part of the plate anchored in the compression zone of a beam....[ Read more ]

The technique of strengthening existing reinforced concrete structures with Carbon Fibre-Reinforced Plastics (CFRP) has become more and more popular over the last couple of decades. Although lots of research efforts have been put on the flexural strengthening with CFRP laminates, most investigations have focused on simply supported beams under 3-point or 4-point bending. These loading conditions, however, may not represent the real situation in practice. In order to have a better understanding of the failure behaviour under practical situations, the present work focuses on CFRP-strengthened beams (i) under quasi-distributed loading , and (ii) with part of the plate anchored in the compression zone of a beam.

To apply quasi-distributed loading to beam specimens, a special wiffle tree system is first designed. From the test results on beams strengthened with relatively thick CFRP, it is found that making the loading more uniform will lead to a change of failure mode from crack-induced debonding to plate end failure. The transition of failure mode is accompanied by a reduction in moment capacity. Existing models for simply supported beams may therefore be unsuitable for the prediction of failure moment under higher load uniformity. On the other hand, for beams strengthened with relatively thin CFRP, as loading becomes more uniform, the failure mode stays as crack-induced debonding, and the ultimate moment capacity is found to increase. Models for simple supported members can hence be applied to give conservative predictions of the failure load.

For strengthened beams with plate ends terminated within the compression zone, it is found that, for beams reinforced with thick plates, increasing the level of longitudinal compression around the plate end may lead to a transition of failure mode from plate end failure to crack-induced failure, with a corresponding enhancement in moment capacity. If failure is due to crack-induced debonding when the plate end is under tension, the presence of compression does not change the failure mode and only slightly affects the ultimate moment. Considering both thin and thick plates, existing models derived for simple supported beams should be applicable to the failure prediction of strengthened beams with plate ends terminated within the compression zone.