PSI - Issue 44

Annalisa Franco et al. / Procedia Structural Integrity 44 (2023) 2246–2253 Author name / Structural Integrity Procedia 00 (2022) 000–000

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based or cementitious mortar). This method is a development of the well-known reinforcement technique of concrete structures which involve steel grids embedded in plaster. Benefits of such systems have been extensively investigated and generally include higher compatibility with substrates compared with other techniques, lower costs, corrosion resistance and better performance at high temperatures, while enhancing permeability and achieving reversibility (Bonati, Franco, Grasso, & Occhiuzzi, 2022). Furthermore, various scientific publications have shown the effectiveness of CRM strengthening in terms of increase of lateral load-carrying capacity, stiffness and ductility of the reinforced masonry members (Corradi, Borri, Castori, & Sisti, 2014; Del Zoppo, Di Ludovico, & Prota, 2019; Gattesco & Boem, 2015). Profound knowledge of material characteristics and their effectiveness under harsh environments is definitely crucial for design (Rizzo, Bonati, Micelli, Leone, & Aiello, 2019; Simeone et al., 2022). Furthermore, qualification of such systems is also foreseen at the European level, through the European Assessment Document 340392-00-0104 (EAD 340392-00-0104:11-2018, 2020) which is the official reference for the CE marking of this construction product, and at the Italian level with a specific guideline for qualification of CRM (High Council of Public Works, 2019). In such documents, qualification of CRM systems involves the characterization of the sole FRP components of the system, which more specifically includes tensile tests in standard conditions but also after ageing of the FRP grids. It is universally accepted that tensile forces are mainly governed by the fibre reinforcements; therefore, tensile testing results are an essential aspect for the determination of mechanical material properties. For fibres made of glass, which are extensively used for textiles and FRPs in civil engineering applications, regulations for the standardized determination of tensile properties are provided by ISO 3341. In this paper, the tensile behaviour of dry glass yarns and FRP grids of two commercial CRM systems is investigated. Tensile tests at different crosshead speeds are carried out in order to highlight the strain rate influence The experimental program was focused on the investigation of the tensile mechanical properties at different displacement rates of the FRP grids and relative constituents glass fibres of two different commercial CRM systems (system “F” and “G” hereinafter). Both grid systems are composed of preformed bars made of fiberglass yarns impregnated with a thermosetting resin. Glass fibres and epoxy thermosetting resin are weaved orthogonally to obtain a monolithic square mesh. Before resin toughen, the mesh is formed by twisting the wires in one direction (warp) around the wires in the other direction, whose fibres, differently, remain parallels (weft). Preformed Glass Fibre Reinforced Polymer (GFRP) meshes are produced in rolls or flat sheets, with twisted fibres wires in the warp direction and parallel fibres wires in the weft one. In the system “F”, the weaving is made with multiple twisted warp and flat non-twisted weft embedded into the warp yarns, while in the system “G” bars with circular cross-section constitute the weft, where warp yarns are weaved around them (Fig. 1). on the systems’ behaviour. 2. Materials and methods

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Fig. 1. FRP grids used in the experimental program. (a) Schematic; (b) System “F”; (c) System “G”.

The geometrical properties of the FRP grids are reported in Tab. 1 and Fig. 1, together with the physical properties of the relative glass fibres.