Shear Deficient RC Beams Retrifitted with Inorganic-matrix Composites

Reinforced concrete (RC) beams of existing framed buildings designed and realized 40-50 years ago are, in frequent cases, characterized by low amounts of transverse reinforcement and need rapid and efficient retrofitting interventions to meet the performance requirements of recent seismic standards. Externally bonded composites represent a popular technique that has the advantage (over concrete section enlargement and steel jackets) to keep the self-weight of the structure relatively unaltered. In this contribution, we present the results of an experimental campaign conducted at the University of Messina on shear deficient RC beams that are strengthened with U-wrapped externally bonded polyparaphenylene benzobisoxazole (PBO) Fabric Reinforced Cementitious Matrix (FRCM) systems applied through different configurations. Ten RC beams are tested up to collapse, including two control beams and eight beams retrofitted with PBO-FRCM systems. Different variables are included in the testing program, including the fiber orientation (90° and 45° with respect to the beam longitudinal axis), the number of layers (one and two), the steel stirrup spacing (200 and 300 mm), and the presence or not of the anchorage. The paper illustrates the main experimental results in terms of shear gain (in comparison to the control beams without FRCM), failure mode, deformation capacity, and fiber exploitation ratio. Additionally, numerical simulation of the tested beams is also performed through a 3D finite element model incorporating a fracture-plastic model for concrete and embedded truss elements with multilinear elastic-plastic material model for steel bars. The FRCM system is simulated via 3D solid elements for the matrix, combined with embedded truss elements for the fibers, the latter incorporating an analytical bond-slip law to numerically reproduce the fiber slippage at the fiber-matrix interface.