Steel Reinforced Grout under uniaxial load: Experimental evidences and numerical modelling

The use of composite materials as structural retrofitting tools has been strongly encouraged by their capability of improving structural performance causing minimum invasiveness and reduced weight increment. For decades, Fiber Reinforced Polymers were considered the most suitable composites for retrofitting purposes but, more recently, technological issues have revealed some drawbacks, mainly related to their applications on masonry substrates. A viable alternative is represented by Fabric Reinforced Cementitious Matrix (FRCM), a class of composites made of high-strength textiles with inorganic matrix. Among them, Steel Reinforced Grout (SRG) systems, made of Ultra High Tensile Strength Steel cords embedded in cement or lime-based mortar, are widely used, particularly for repairing or strengthening masonry constructions. Qualification tests and acceptance criteria of these composites have been recently proposed. Numerical simulations of current available experimental test procedures need to be performed to provide a more rigorous insight into the mechanisms that control the composite response up to failure, namely the brittle cracking of the matrix, the ductile response of the steel and the debonding at the mortar-fabric interface. These aspects not only affect the microscale, but are indeed responsible for the macroscopic response of the composite. In this work a finite element simulation of direct tensile tests on SRG systems is presented. Two different gripping methods have been considered, the clamping-grip and the clevis-grip, which identify two standardized test procedures according to RILEM and ACI respectively. Numerical results are first compared with the experimental outcomes to assess the accuracy of the model in reproducing the quantitative and qualitative aspects of composite tensile response. Then, the effects of different boundary conditions on failure mechanisms are investigated, analysing damage and stress patterns in the constituents.