PSI - Issue 78

Francesca Mattei et al. / Procedia Structural Integrity 78 (2026) 2169–2175

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actions, with the retrofit panels carrying almost all the shear demand and relieving the existing masonry walls, which then acted as secondary elements. The connection between the retrofit panel and the existing wall was designed with L-shaped rebars grouted with epoxy resin, ensuring adequate shear transfer capacity. Buckling analyses confirmed no stability issues for the selected configuration, though second-order effects may become relevant for longer or thinner panels. Two testing phases, focused on the performance of the single retrofit panel (Phase 1) and on the combined performance of the existing + retrofit system (Phase 2), were organized. The first experimental campaign (Phase 1), again described in Caprili et al. (2024), investigated the mechanical performance of the retrofit panel in isolation through axial and diagonal compression tests, out-of-plane buckling tests, and in-plane monotonic and cyclic tests. Axial and diagonal compression tests confirmed the adequacy of the design assumptions, while highlighting the sensitivity of strength and stiffness to casting quality. Out-of-plane tests, designed to be representative of slender panels in existing buildings (L/H ≈ 1:2), showed that no buckling issues are expected for the nominal 100 mm concrete thickness. In-plane tests on panels with L/H ratios of 1:2, 1:1, and 4:3 demonstrated increasing lateral capacity and stiffness with decreasing slenderness, with failure localised at the connection between the panel and the foundation, specifically failures of vertical rebars in tension. Cyclic tests exhibited the typical pinching behaviour of RC shear walls, with some asymmetries in load – drift response attributed to local imperfections in concrete casting and reinforcement placement. The result from Phase 1 campaign allowed to assess the reliability of current guidelines D.M. (2018), Circolare n.7 (2019), Linee Guida (2011) normally adopted for new constructions in lightly reinforced concrete walls with formwork blocks. Phase 2, currently in progress, involves monotonic and cyclic tests on the combined system, existing walls plus retrofit panels, considering two masonry typologies representative of the majority of buildings constructed more than 50 years ago: full brick w ith clay mortar and hollow bricks of the ‘Doppio UNI’ type. All tests were performed at the Laboratorio Ufficiale per le Esperienze sui Materiali da Costruzione of Pisa University; the specimens, as well as the other components required for the setup and t ests’ execution were provided by Paver Costruzioni s.r.l . The first monotonic test on a combined system with a ‘Doppio UNI’ hollow brick wall is presented in the following section and compared with the numerical simulation developed in Caprili et al. (2024) using a nonlinear model in OpenSees®, McKenna et al. (2000). Experimental campaign on the joined system Phase 2 involves testing the combined system with three geometric (L/H) ratios, 1:2, 1:1, and 4:3, constructed using 23.5 cm-thick formwork blocks and a nominal concrete core thickness of 10 cm. Each specimen incorporates a rigid reinforced concrete foundation and RC top beams connecting the two adjacent walls. During testing, both the masonry wall and the RC wall are subjected to vertical loads simulating real service conditions. The design, test setup, and results for the specimen with an L/H ratio of 1:2 are presented in the following section. Design of the specimen The height of the panel, excluding the RC top beam, was 284 cm, with a length of 150 cm. Specimen was equipped with a foundation system and an RC top beam for masonry and RC panel.