PSI - Issue 44

Matteo Canestri et al. / Procedia Structural Integrity 44 (2023) 2198–2205 Canestri et al./ Structural Integrity Procedia 00 (2022) 000–000

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1. Introduction The severe vulnerability shown by many historical masonry structures is one of the key driving aspects of risk assessment. For this reason, in recent years, the efficiency of many retrofitting solutions, like Steel Reinforced Grout (SRG) and Textile Reinforced Mortar (TRM) composites, applied on masonry, has been thoroughly assessed by many authors. Tests were conducted on strengthened masonry panels to study the out-of-plane and in-plane behavior (Ismail and Ingham, 2016; Bellini et al., 2018, Donnini et al., 2021), proving the beneficial effect of the reinforcing systems (Incerti et al., 2019; Ferretti et al., 2021; Ferretti and Mazzotti, 2021; Garcia-Ramonda et al., 2022). Several studies also evaluated the effectiveness of SRG and TRM applied to axially compressed members like columns. Enhancing the stability and ductility of these elements is particularly important, since they are, in fact, the most stressed and exposed members during an earthquake action and their failure can easily trigger a global collapse of the building. Among others, Ombres and Verre (2018, 2020) proved the efficacy of multiple SRG layers in confining axially loaded masonry elements and studied the influence of the overlapping length on the failure mode. Their results were also validated in other scientific research, which further examined the confinement efficiency of these materials (Carloni et al., 2014; Santandrea et al., 2017; Sneed et al., 2019). Many authors tried also to predict the behavior of confined masonry columns with analytical models, firstly formulated for structural elements confined with Fiber Reinforced Polymers (FRP) (Micelli et al., 2004; Corradi et al., 2007). Later on, in few works, these models were adapted and modified to properly account for the behavior of alternative strengthening solutions like TRM and SRG (Murgo and Mazzotti, 2019). In this work, the confinement action provided by SRG lateral wrapping on masonry columns was investigated, taking also into account the influence of the number of layers. The obtained experimental results were then compared with analytical predictions, derived by adapting the Spoelstra and Monti (1999) approach – formulated for FRP-strengthened concrete columns – to the case of SRG-strengthened masonry columns. 2. Description of the experimental campaign The structural performances of SRG wrapping on small scale masonry columns were investigated through monotonic uniaxial compression tests. A total of eight specimens were built and tested to failure. One unreinforced sample acted as a reference, while a variable number of overlapping layers was studied, i.e., from 1 to 3. 2.1. Strengthening layouts Masonry columns, whose geometrical dimensions are reported in Fig. 1, were built by alternatively stacking two solid bricks (250×120×55 mm 3 ) on nine different layers, with horizontal and vertical joint thickness of 10 mm.

Fig. 1. (a) Construction of the column sample, (b) sample dimensions (expressed in mm), (c) scheme of the strengthening layouts.