PSI - Issue 62

Paolo Zampieri et al. / Procedia Structural Integrity 62 (2024) 446–453 Paolo Zampieri/ Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction

In FRCM composites increase the performance of the existing structures in different way: axial (Bournas, et al, 2007; Trapko, 2013), torsional (Alabdulhady, et al, 2017), flexural (D'Ambrisi & Focacci, 2011; D'Antino & Poggi, 2021) and shear (Blanksvärd, et al., 2009; Azam & Soudki, 2014; Gonzalez-Libreros, et al., 2017) with only the external application of these composites. Debonding between the reinforcement-substrate interface is one of the typical failure modes in both studies conducted for concrete (Awani, et al, 2015; Zou, et al, 2019) as well as for masonry (Grande & Milani, 2021; Wang, et al, 2021) when they are reinforced with FRCM. The performance of the structures being strengthened depends directly on the stress transfer mechanism between the reinforcement and the substrate. This mechanism is very complex to investigate and in the case where the substrate is curvilinear (e.g. to reinforce an arch) a further degree of complexity is added as an additional stress component is created at the interface (substrate-matrix and fibre-matrix). The performance of structures strengthened with composite materials can be improved by postponing the debonding with the use of spike anchors that counteract the detachment stresses of the strengthening system; several studies show the improvement on flat concrete surfaces (Kalfat, et al, 2013; del Rey Castillo, et al., 2022), which present higher values in curved surfaces than in straight ones and only few works investigate the bond behaviour between FRCM and curved substrate (Malena & de Felice, 2014; De Santis, 2017; Malena, 2018; Rotunno, et al., 2018; Rotunno, et al., 2019; Bertolesi, et al., 2020; Bertolesi, et al., 2021). In masonry arches, the use of fibre-reinforced composite materials on the extrados, intrados or both, increases the load-bearing capacity of the structure because the strengthening system opposes the formation of the vault collapse mechanism (Galassi, 2018; Galassi, January 2018; Zampieri, 2020; Zampieri, et al., 2020; Simoncello, et al., 2020). Hinge formation appears to be the most likely failure mode of unstrengthened masonry arch structures subjected to external forces (Simoncello, et al., 2022). This paper presents the results obtained from direct shear tests performed on curved masonry specimens strengthened with a fabric-reinforced cement matrix (FRCM). In particular, the experimental campaign shows the effects of spike anchors in the load transfer mechanism between the composite and the substrate.

2. Materials and methods 2.1. Specimen’s properties

The masonry prisms consisted of soft pressed fired clay bricks (a =110 mm, b =245 and c =55 mm, Fig. 1) and mortar joints with a minimum thickness (t 1 ) of 10 mm and a maximum thickness (t 2 ) that varied according to the radius of curvature (R). The FRCM composite's bond behaviour is examined through single lap shear tests conducted on specimens with four distinct bonded lengths (l b =150, 200, 250, and 350 mm) , constant bonded width (w b =80 mm) and three different radius of curvature (R ∞ =∞ mm; R 1 =1875 mm; R 2 =1508 mm). Moreover, this experimental campaign investigates how the bond properties are affected by the dry carbon fiber spike anchors (S.A.). As a result, two anchor depths l a (l a = b/2 and b, Fig. 1), and three S.A. configurations n a (n a =0, 1 and 2, and Fig. 1) were evaluated.

Fig. 1 Geometric features of the curved masonry prims strengthened by FRCM (dimensions in mm)