PSI - Issue 44

Marta Del Zoppo et al. / Procedia Structural Integrity 44 (2023) 2158–2165 Del Zoppo et al./ Structural Integrity Procedia 00 (2022) 000 – 000

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walls (Augenti and Parisi 2010). Even in reinforced concrete buildings, the out-of-plane failure of unconfined infill walls is commonly observed (Braga et al. 2011). To face this issue, several retrofit techniques have been developed and largely used in recent years adopting traditional (i.e., reinforced plasters) or innovative composite materials (i.e., Fibre Reinforced Polymers, FRP). In the last decade, the use of inorganic composite materials for masonry structures is significantly increased due to sustainability concerns and a great compatibility with the substrate. Fibre Reinforced Cementitious Matrix (FRCM) systems represent a novel and effective technique for both the in-plane (Del Zoppo et al. 2020, Castori et al. 2021, among others) and out-of-plane ( D’Ambra et al. 2018, D’Antino et al. 2018 ) strengthening of masonry walls. However, the application process of the grid is not always immediate and can lead to premature delamination problems, if not properly installed. A promising alternative to FRCM is represented by the Fibre Reinforced Mortars (FRM), which are mortars containing short fibres randomly dispersed. The advantage of such strengthening system is the easy application, as it can be applied as a normal plaster. The few experimental results available in literature attested the effectiveness of FRMs for the in-plane shear strengthening of masonry walls (Del Zoppo et al. 2019, Lucchini et al. 2020, among few others). However, only a few experimental studies have been conducted to assess the effectiveness of FRMs for the out-of-plane strengthening of walls (Colombo et al. 2016, Najafgholipour et al. 2016). The present study aims at investigating the effectiveness of FRMs for the out-of-plane flexural strengthening of solid clay brick masonry walls. Results from a first stage of an experimental campaign carried out on three specimens tested out of their plane are herein presented and discussed. Two walls are strengthened with FRM (i.e one side or double side strengthening layout) and one is tested as a control specimen. Experimental results are compared to point out the effectiveness of such strengthening system. 2. Experimental campaign Three solid clay brick masonry walls have been realized and tested out-of-plane (OP) at University of Naples Federico II. The overall dimensions of the specimens is 116x118x12 cm (i.e., single leaf panels). After the curing period, two specimens have been strengthened with a lime-based Fibre Reinforced Mortar (FRM). Two strengthening configurations have been studied: (i) double-side strengthening (termed FRM_2S) and (ii) single-side strengthening (termed FRM_1S), being the latter sometimes forced by aesthetic/architectural limitations that prevent the application of the strengthening system. The overall thickness of the FRM layer is 15mm. The last specimen was tested in the as-built configuration (and termed URM) as a control specimen to assess the effectiveness of the strengthening system. 2.1. Materials mechanical properties Solid clay bricks of typical dimensions 24x12x5.5 cm are adopted to build the specimens. The average compressive strength of the clay bricks, derived from compressive tests on cubic samples, is 22.3 MPa. The bed joint mortar (average thickness 15mm, class M5) has been also tested to derive the average compressive strength: 7.3 MPa. The FRM adopted to strengthen the panels is made by a lime-based mortar with embedded short glass fibres (length 19mm, volumetric ratio less than 2%). Compressive tests and direct tensile tests on FRM samples have been performed after the curing period to assess the mechanical properties of the strengthening system. From experimental results, the average compressive strength of the FRM is 23.2 MPa whereas the peak tensile strength, corresponding to the cracking of the mortar under pure tensile stress, is 0.7 MPa. 2.2. Test setup, instrumentation and loading protocol A novel setup has been designed to perform out-of-plane tests on masonry walls, as shown in Fig. 1. The setup is conceived to perform a four-point bending test combined with compressive axial load on a simply supported beam. Indeed, this test arrangement is suitable to assess the flexural capacity of masonry walls out of their plane (Iuorio et al. 2021). The horizontal load is applied by means of a servohydraulic actuator and it is splitted in two lines of load uniformly distributed over the width of the masonry panel. The horizontal load is spread over the wall by means of