Delamination Buckling of FRP Strips in Strengthened Structural RC Beams and Masonry Walls

Abstract

This paper deals with delamination buckling of fibre-reinforced polymer (FRP) strips glued to reinforced concrete (RC) beams or to heterogeneous material as masonry. In the field of rehabilitation of existing civil structures, the strengthening using composite materials is becoming a frequent technique although many points have not yet been clarified. The delamination of FRP strips' layer can be often the cause of loss of the strength capacity in strengthened elements. In general, the delamination is due to loss of adhesion of FRP on the adherent material under tensile loading. This type of delamination foresees a slip of FRP strip and development of fracture energy until the detachment. Delamination buckling of FRP strips is instead due to compression loading. Although the FRP is usually adopted to improve the tensile capacity, in civil structural elements subjected to cycle loading, as RC frames in seismic areas or masonry cross walls, the loading is cyclic and the strengthening of FRP strips may be subjected to compressive stresses with separation of the layer from the adherent element. This type of delamination may significantly influence the strength, stiffness and stability. In this paper experiments on the strengthening of RC beams and masonry walls with GlassFRP strips are shown further, analytical and numerical analysis have been developed to study this mechanism of delamination which too often has been missed in the design of strengthening with FRP strips.