PSI - Issue 44

Rebecca Fugger et al. / Procedia Structural Integrity 44 (2023) 2166–2173 Author name / Structural Integrity Procedia 00 (2022) 000–000

2167

2

formulations proved to provide a proper-and-safe estimate of the strength of masonry walls reinforced with FRCM and subject to shear, thanks also to the calibrated model and safety coefficients they are equipped with, as specified in ACI 549.6R-20 (2020) and Meriggi et al. (2021). However, the real resisting mechanism activating in a shear loaded FRCM-strengthened wall is still unclear. Furthermore, for enhancing the reliability of the aforementioned formula, it would appear useful to have information on the shear strength of the FRCM composite not bonded to substrate, to be adopted, possibly together with the FRCM bond strength, for estimating the FRCM shear contribution to the overall resistance of the strengthened wall. Within this framework, research efforts should be devoted to the investigation of the shear behaviour of the FRCM not bonded to substrate, that is of the shear stress transferring mechanism between matrix and fabric. The comprehension of this mechanism, together with the well-established understanding of the FRCM-to-substrate stress transferring one, may enhance the knowledge on the shear behaviour of masonry walls retrofitted with mortar-based composites – Carloni et al. (2015), Nerilli and Ferracuti (2018). This topic has been numerically investigated in Nerilli et al. (2020), (2021), whilst the experimental counterpart is still lacking. A first attempt of experimental research was done by Sisti et al. (2019), where square shaped FRCM and Composite Reinforced Mortar (CRM) – De Santis et al. (2019) – specimens were tested under quasi-static cyclic shear loads. Nevertheless, it is not yet clear how the individual components of an FRCM – fabric and mortar – behave under shear load, nor to what extent they contribute. Recent experimental results - Angiolilli et al. (2020), Ferretti and Mazzotti (2021) - have demonstrated the non-negligible contribution of the mortar matrix in increasing the strength of the FRCM. In this context, the paper proposes an innovative experimental set-up for studying the behaviour of the FRCM subject to shear. To this aim a novel setup was designed, consisting in a parallelogram frame made of coupled steel plates connected by four hinges. Tests were performed on specimens made of either bare textile or mortar or composite with dimensions of 200mm×200mm. Four basalt FRCM systems have been considered, they comprise a bidirectional balanced mesh with either 9mm or 15mm grid spacing embedded within either lime-based or cement-based mortar. The shear response of the textile and mortar alone and of the FRCM composite was studied. Furthermore, in order to detect the displacement and strain fields Digital Image Correlation (DIC) – Schreier et al. (2009), Caggegi et al. (2016) – was applied and computed with the software Ncorr according to Blaber et al. (2015). DIC demonstrated to well detect the crack pattern throughout the duration of the test and at each loading step. 2. Experimental overview Tests were performed on specimens made of either basalt textile-only, labelled as T9 and T15 for textile with 9mmx9mm and 15mmx15mm grid-spacing respectively, or mortar-only labelled as M-L for lime-based and M-C for cement-based. Furthermore, four types of composite specimens were tested, named as T9-L, T15-L, T9-C and T15 C. Specimens have dimensions of 200mmx200mm, those of either mortar-only or composite have 10mm thickness (Figure 1). Composite specimens are composed by 3 layers, the bottom and the upper are made of mortar (5 mm thick each), while the middle is the basalt textile. Mortar-only, and composite specimens were manufactured in single 3D printed square-shaped polylactide (PLA) formwork and demoulded after 2 days, cured in water for 26 days, and finally, left for 7 days in laboratory conditions (18-20°C temperature and relative humidity of about 50-60%) before testing. Figure 2 shows the steps made during the casting process together with the formwork. Two tests per each type of the aforementioned specimens were carried out. Mortar-only and composite specimens were afterwards analyzed trough Digital Image Correlation (DIC). Indeed, they were painted with a speckle pattern of randomly distributed black dots on white background, as shown in Figure 2e.