Experimental study on effect of EBR and EBROG methods on debonding of FRP sheets used for shear strengthening of RC beams

摘要

Rehabilitation and retrofit of structures have been widely used in buildings since many years ago. In recent years, Fiber Reinforced Polymer (FRP) composites have been utilized to rehabilitate and retrofit various types of structures. Due to the desirable properties of FRP composites such as high strength and light weight, engineers have shown great tendency to use FRP sheets extensively in reinforced concrete structures for both shear and flexural strengthening. Nevertheless, premature failure due to debonding of FRP sheets from the concrete surface is one of the major challenges in using FRP composites in strengthening projects. Surface preparation of concrete in order to provide proper bond between concrete surface and FRP sheet can put off debonding up to a limited stage. However, in most investigations which RC beams are strengthened in shear with FRP sheets, the debonding has been finally observed. In the current study, the effects of surface preparation on shear strengthening of RC beams are investigated; also the substitute of conventional surface preparation with grooving method is considered. Experimental specimens consisted of 32 small scales concrete beams which were subjected to 4-point loading test. The results revealed that although the surface preparation of concrete before attaching the FRP sheets often does not prevent from the debonding, but it can delay debonding even slightly and, accordingly, increase carrying loads of beams up to 12%. Furthermore, the results showed that grooving method performs better than surface preparation; so that the detachment of FRP strips did not occur in any of beam specimens strengthened by this method and the weakness of beams in shear disappeared and flexural failure became dominant failure mode.