Flexural strengthening of RC beams using external unbonded rebar: an experimental investigation

Flexural strengthening of reinforced concrete (RC) beams is an important research topic due to its huge practical demand. In the present study, a new flexural strengthening method for RC beams, called the Shear-key Mounted Unbonded Rebar (SMUR) technique, is proposed and its effectiveness is examined through an experimental investigation. A total of 12 RC beams were cast and tested under four-point loading. Ten were strengthened and the remaining two the original or control beams. Before casting the RC beams, their constituent materials, such as cement, aggregate and rebar, were tested to ensure the quality of casting. The beams were strengthened with unbonded rebars attached to their tension faces through shear keys. One of the main advantages of the proposed technique was its speed and ease of application. As well as its effectiveness, the effects of other important aspects, such as the size and location of the rebar, were also examined. It was found that the proposed method noticeably enhanced the flexural capacity of a control beam. The ultimate load capacity of a strengthened beam was 60% higher than that of a control one. The flexural performances of the beams could be further improved by increasing the bar size and its location. The welding and conventional flexure were the dominant modes of failure in the strengthened beams.