PSI - Issue 44

Ciro Del Vecchio et al. / Procedia Structural Integrity 44 (2023) 1411–1418 Ciro Del Vecchio et al. / Structural Integrity Procedia 00 (2022) 000 – 000

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This may help in promoting a uniform distribution of lateral loads to all the lateral resisting systems avoiding local collapses and premature failures. This can be done by improving the connection between the walls and the horizontal structural systems (i.e. slab or vaults) and by enhancing the connection between orthogonal walls. Classic techniques such as the use of reinforced concrete corbel, steel ties or steel anchors nailed in the masonry walls can be useful to this scope (Tomaževič et al. 1996) . In the recent years, the introduction of financial incentives by the Italian government boosted the implementation of retrofit interventions to improve the seismic risk class of existing buildings. Since that the main focus of these interventions are the residential buildings, the main challenge is to enhance the seismic performance with low impact in terms of level of disruption and interruption of building functionality. This gave new emphasis to the development of innovative techniques that may effectively increase the seismic response being applicable mainly from the exterior of the building or with minimum level of disruption. In this context, the use of mechanical anchors can be a sound-effective solution conjugating the need of improving the connection between orthogonal walls or between the walls and the horizontal systems with a low level of disruption during their installation. Many studies can be found in literature addressing the experimental (Arifovic and Nielsen 2006; Silveri et al. 2015; Ceroni et al. 2016, 2017; Burton et al. 2021) and analytical characterization (Arifovic and Nielsen 2006; Ceroni and Di Ludovico 2020) of the performance of mechanical anchors injected in masonry elements. Although the significant effort resulted in relevant knowledge advances on the pull-out behavior of injected anchors, many aspects still need to be investigated. For instance, a reduced distance between the anchor and the closest edge of wall can be triggering for a premature splitting failure that may compromise the design performance of the anchor. Although some recommendations (i.e. guaranteeing a distance from the edge hedge higher than 1.5 the anchorage length, fib bulletin 58 2011; ACI 318 2019)and analytical models (Arifovic and Nielsen 2006; Ceroni and Di Ludovico 2020)are available in literature, the strength against splitting of mechanical anchors injected in tuff masonry walls is still difficult to be predicted. To investigate the pull-out response of steel anchors injected in yellow tuff masonry, an experimental program on full-scale masonry wallet was designed with the main scope to identify the influence of the axial pressure on the strength of anchors with a splitting failure mode. The testing program was realized at the Laboratory of Materials and Structures (LAMAS) belonging to the University of Sannio in Benevento and consisted of six pull-out tests performed in a wall subject to axial stress varying in the range 0.10 MPa – 0.20 MPa. The anchors were realized in the center and at the edge of the wall to simulate different boundary conditions and to assess their influence on the strength and failure mode. 2. Experimental program The experimental program consists of six pull-out tests on steel bars injected in a full-scale masonry wallet 1.1 m long, 1.1 m height and 0.35 m thick. The masonry wallet was built using yellow tuff stones (360 mm x 250 mm x 110 mm) spaced by10 mm thick cement-based mortar joints. The wall dimensions, the texture, as well as the position of anchors are reported in Fig. 2 along with the reaction frame (in red) and its positioning in the configuration for testing central (1, 3) or edge (2, 4, 5, 6) bars. Holes with 30 mm diameter were drilled for a total depth of 330 mm to guarantee the installation of the anchors with an embedded length, l e , of 300 mm. The layout of holes is reported in Fig 2 (left). The central holes (1, 3) were realized at a distance of 550 mm (>1.5 l e ) from the edge to avoid the splitting failure allowing the full development of the anchorage strength. They were used as benchmark to assess the pull-out strength. The lateral holes (2, 4, 5, 6) were realized near the edge at a distance of 180 mm, significantly lower than 1.5l e to induce the splitting failure.