Strengthening reinforced concrete beams with external unbonded bars: experimental investigation

In an earlier study the authors outlined a strengthening technique for reinforced concrete beams using external unbonded reinforcement. It was shown that the technique could provide useful enhancements in load capacity in all but heavily reinforced cross-sections. The technique offers advantages in speed and simplicity of installation over other, established, strengthening techniques. The earlier work used deflectors in order that supplementary external bars would follow the curvature of the original beam. If these deflectors could be dispensed with, further simplifications could be made in installation procedures. A more extensive programme of physical testing and associated modelling of behaviour has now been performed in order to further explore the capabilities of the technique and to determine the circumstances under which deflectors should be installed. The paper provides a general description of structural behaviour of beams strengthened using the technique. Results of 27 physical tests on strengthened reinforced concrete beams are reported and compared with those from a further eight reference specimens. It is shown that the technique can provide greater strength enhancements to lightly reinforced sections and that provision of deflectors enhances efficiency. The danger of sudden collapse is found to be no greater than that for equivalent conventionally reinforced beams. The various parameters which affect strength enhancements attainable with the technique are reviewed.