Behaviour of RC beams with a fibre-reinforced polymer (FRP)-strengthened web opening

Abstract

The beam opening (BO) technique, which involves (1) the creation of a web opening in the beam to weaken its flexural capacity and (2) the fibre-reinforced polymer (FRP) shear strengthening around the opening to avoid shear failure of the beam, was proposed to realize the strong column-weak beam hierarchy in existing reinforced concrete (RC) frames, which were designed using previous codes and thus violated such hierarchy. In the present study, six large-scale T-section beams with a web opening of different sizes and made by different methods (pre-formed and post-cut) were tested to assess the effectiveness of BO technique and the test results are presented. The experimental study shows that the post-cutting method is feasible for making web openings in existing RC beams, the BO technique can effectively reduce the flexural capacity of the beam to the desired value if the size of web opening is appropriate, and the FRP strengthening can well compensate the loss of shear capacity and ductility of the beam caused by the creation of web opening. The present study provides a basis for the safe use of BO technique to achieve the strong column-weak beam hierarchy in existing RC frames.