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 a FRCM system made by PBO (short of Polypara-phenylene-benzo-bisthiazole) fabric meshes with dry fiber strands disposed along two orthogonal directions bonded to concrete surfaces with a cement based mortar.A total of 9 reinforced concrete beams strengthened both in flexure and shear with PBO-FRCM have been tested varying both the shear strengthening configuration (continuous and discontinuous U-wrapped strips) and the PBO reinforcement ratio.The main issues focussed in the paper are: (i) the effectiveness of the PBO-FRCM system as shear strengthening system, (ii) the shear performance, including failure modes, of reinforced concrete beams strengthened in terms of the PBO, the internal transversal steel reinforcement (steel stirrups), the internal longitudinal steel reinforcements and the concrete strength, (iii) the interaction between transversal internal steel and external PBO-FRCM shear reinforcements and, by comparison with experimental results, (iv) the reliability of models found based on the Ritter–Morsch criteria failure to predict the shear capacity of PBO-FRCM strengthened reinforced concrete beams.