Behaviour and strength of RC beams shear-strengthened with externally bonded FRP reinforcement

Strengthening of RC structures using externally bonded (EB) fibre-reinforced polymer (FRP) composites has become a popular structural strengthening technique over the past two decades. This thesis presents a systematic study into the analysis, behaviour, and design of RC beams shear-strengthened with EB FRP reinforcement. The scope of the thesis is limited to shear failures associated with the development of shear tension cracks (or diagonal tension cracks), and in particular the two failure modes of shear failure by FRP tensile rupture and shear failure by FRP debonding. The thesis starts with an extensive literature review, revealing the deficiencies of existing studies on RC beams shear-strengthened with FRP. It then presents an experimental study on RC beams shear-strengthened with complete FRP wraps that were either fully bonded to the beam or intentionally left unbonded on the beam sides; these beams all failed by FRP tensile rupture. The test results illustrate the advantage of wraps that are not bonded on the beam sides and reveal the adverse shear interaction between FRP wraps and concrete. The next few chapters deal with analytical/numerical investigations based on realistic physical assumptions to arrive at a new shear strength model for the FRP debonding failure mode. In particular, mobilization factors are developed to properly account for the effects of shear interaction between FRP strips and steel stirrups. The new shear strength is shown to predict existing test results well. The final part of the thesis is concerned with the development and application of an advanced finite element (FE) model capable of accurate modelling of the behaviour of shear-strengthened RC beams. The present FE model overcomes various limitations of the existing FE models for such beams, particularly in the modelling of localised concrete cracking. Numerical results obtained from the FE model provide additional support for the proposed shear strength model for the FRP debonding failure mode. The proposed FE model is the most advanced model available for debonding problems in FRP-strengthened RC structures and can be deployed to study many issues such as the effect of preloading in such beams in the future.