Strengthening for Shear of RC Beams by External Plate Bonding

The main focus of this paper is to investigate the applicability of external plate bonding to strengthen in shear reinforced concrete (RC) beams without any internal shear reinforcement. Extensive test data are presented to evaluate the feasibility of the technique when the externally bonded tension plate is made of steel or of glass-fibre-reinforced polymer. A total of 12 beams, 150 x 250mm in cross-section, were tested over an effective span of 2800mm at a shear span-to-efective-depth ratio of 3.0. The influence of various parameters, such as the plate material properties, amount of internal stirrups, lateral confinement of the compression zone, and amount of flexural reinforcement on the effectiveness of external plate bonding, has been critically assessed. The results show that, with properly designed, externally bonded plates in the form of end anchorages, U-shaped strips/stirrups, and confinement plates for the compression zone, it is possible to transform the brittle shear failure of a beam without any shear reinforcement into a ductile flexural failure. It is shown that the conventional RC beam theory can predict very satisfactorily the ultimate failure load of such a strengthened beam failing in flexure. Further research is, however, needed to quantlfy the shear contributions of the various types of bonded plate.

Professor R.N. Swamy, P. Mukhopadhyaya and C.J. Lynsdale