Structural performances of reinforced concrete beams strengthened in shear with a cement based fiber composite material

The shear capacity of reinforced concrete beams strengthened with cement based composite materials(FRCM, Fabric Reinforced Cementitious Matrix) was investigated in the paper. The analysis refers to aFRCM system made by PBO (short of Polypara-phenylene-benzo-bisthiazole) fabric meshes with dry fiberstrands disposed along two orthogonal directions bonded to concrete surfaces with a cement basedmortar.A total of 9 reinforced concrete beams strengthened both in flexure and shear with PBO-FRCM havebeen tested varying both the shear strengthening configuration (continuous and discontinuousU-wrapped strips) and the PBO reinforcement ratio.The main issues focussed in the paper are: (i) the effectiveness of the PBO-FRCM system as shearstrengthening system, (ii) the shear performance, including failure modes, of reinforced concrete beamsstrengthened in terms of the PBO, the internal transversal steel reinforcement (steel stirrups), the internallongitudinal steel reinforcements and the concrete strength, (iii) the interaction between transversalinternal steel and external PBO-FRCM shear reinforcements and, by comparison with experimentalresults, (iv) the reliability of models found based on the Ritter–Morsch criteria failure to predict the shearcapacity of PBO-FRCM strengthened reinforced concrete beams.