PSI - Issue 11

Francesca Giulia Carozzi et al. / Procedia Structural Integrity 11 (2018) 355–362 F.G. Carozzi et al. / Structural Integrity Procedia 00 (2018) 000 – 000

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1. Introduction

Historical masonry structures are composed of brittle materials and often present low mechanical properties and damages in the bricks or in the mortar joints. Moreover, these elements present low resistance to seismic events. Different reinforcement techniques were developed and applied on masonry and concrete structures to improve their performance and resistance to seismic events. Composite materials like Fiber Reinforced Polymers (FRP) represent an effective technique that presents many advantages like the high resistance, lightness, speed of execution. In the last decades, different composite systems were developed to retrofit these structures with more compatible and sometimes reversible materials. The more common systems are Textile Reinforced Mortar (TRM), Fabric Reinforced Cementitious Matrix (FRCM) and Steel Reinforced Grout (SRG); they are composed of different fiber textiles (glass, carbon, PBO, steel) applied with lime or cementitious matrices. In the literature a lot of research works are available on the investigation of mechanical and bond properties of this composite systems (Peled et al; 2008), (Contamine et al., 2011), (D’Antino et al., 2014), (Carozzi et al., 2015), (De Santis et al., 2015). These reinforcement systems are mainly used to improve the masonry walls resistance in case of out-of- plane bending (D’Ambrisi et al., 2014), in plane shear stresses (Prota et al., 2006), retrofitting of arches and vaults (Carozzi et al., 2018). The most common test set-up used to investigate the in-plane performance of masonry walls is the diagonal compression. The wall is located on two steel shoes and the load is applied with a jacket on a diagonal (Parisi et al., 2013), (Babaeidarabad et al., 2016), (Menna et al., 2015). The displacements and strains are usually measured on the tensile and compressive diagonals with LVDTs or strain gauges (Marcari et al., 2017). (Almeida et al, 2015) studied also the effect of a cycling loading application to assess the stiffness degradation during each cycle and the progressive failure of the strengthening systems. Few experimental campaigns were performed in-situ. The in-situ tests are obviously more complicated due to the variability of the masonry mechanical properties, the geometry and texture of the walls and to the maintenance status of the structure. In (Borri et al., 2011) a series of experimental diagonal compression tests performed on different masonry panels in Umbria and Abruzzo (central Italy) was described. In the same work the mechanical behavior of a particular masonry type and the effectiveness of reinforcing systems with either traditional or innovative techniques were investigated. In the present paper a series of diagonal compression tests were performed in-situ on panels cut from an ancient masonry structure. One panel was tested without any treatment in order to define the mechanical properties of the masonry, and three samples were reinforced with different TRM systems. The paper describes the mechanical characterization of the reinforcement systems, the in-situ experimental results and the analysis of the performance of these reinforcement systems. 2. Samples geometry and properties The in-situ experimentation was performed on elements cut from an ancient masonry structure (Fig. 1a) located in Finale Emilia (Modena), in the north of Italy. The four panels presented nominal dimensions equal to 1000x1000x300 mm 3 and were characterized by the presence of two running bond masonry panels coupled by means of a 10 mm thick vertical layer of mortar. Some diatons were used to enhance the connection between the two masonry leafs. The original component materials were very poor, the mortar joints were irregular and the presence of holes was noted. Moreover, the masonry texture was quite irregular and the bricks presented no constant dimensions (Fig. 1a). Compressive tests were performed to characterize the mechanical properties of the bricks. Cube samples (dimensions 40x40x40 mm 3 ) were extracted from a brick to perform compressive tests. In many cases the internal part of the bricks was characterized by the presence of holes and impurity elements. Despite this, the compressive strength of the undamaged samples was around 40 MPa. Four masonry panels were cut, one was tested without any treatment as “control” and three elements were reinforced with different TRM systems (Table 1). Both the sides of two samples were reinforced with TRM systems composed of two different glass fiber grids (named G-TRM and cG-TRM) and a lime mortar. The third sample was reinforced on one side with TRM system and on the other side with a Near Surface Mounted (NSM) system. The sample preparation is showed in Fig. 1b.