Abstract
The in situ rehabilitation or upgrading of reinforced concrete (RC) members using bonded steel plates has been proven in the field to be an effective, convenient and economic method of improving structural performance. However, disadvantages inherent in the use of steel have stimulated research into the possibility of using fibre- reinforced polymer (FRP) materials in its place, providing a non-corrosive, more versatile strengthening system. The aim of this investigation was to provide a detailed study of the flexural strengthening of RC beams using FRP plates. Experimental testing of 1.0 m length specimens was used to illustrate the feasibility and general characteristics of external FRP strengthening. A parametric study was also carried out to evaluate the influence of basic geometric and material parameters on overall performance. Larger-scale 2.3 m length beams were used to confirm the general behaviour observed in the 1.0 m tests. The structural effects of pre-tensioning the FRP plate prior to bonding to the beam were also examined. Although moderate increases in flexural rigidity and strength over a non-prestressed member were attained by the use of this technique, the greatest influence observed was restraint on the initiation and development of cracking. The performance of the component materials and overall strengthened system under sustained load application and adverse environmental conditions was considered experimentally. The results, although somewhat limited, suggest that environmental deterioration of the mechanical properties of bulk adhesive specimens does not necessarily imply a degradation of the bond performance in situ or a reduction in the long-term structural behaviour of the strengthened member. Similarly, the viscoelastic nature exhibited by the epoxy adhesive when tested in isolation did not appear to affect the time-dependent behaviour of the strengthened member; the addition of the externally bonded FRP plate appeared to have only beneficial influences on long-term behaviour. The effectiveness of theoretical methods of predicting FRP strengthened beam response to load application was finally assessed. A simple, iterative analytical technique was generally found to provide good correlation with the global behaviour determined experimentally. Theories proposed to account for the occurrence of premature failure of steel plated beams were evaluated; these appear to be unsuitable for FRP strengthened members. Use of the finite element (FE) method for predicting flexural response was also investigated. In this case, agreement with behaviour observed in testing was found to be poor. This was attributed to the representation of material response incorporated in the FE package.