PSI - Issue 78

Francesco Bencardino et al. / Procedia Structural Integrity 78 (2026) 1396–1403 Author name / Structural Integrity Procedia 00 (2025) 000 – 000

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double pendulum at the bottom. A series of instruments were employed in order to check deformations/displacements exhibited during the procedure (see Fig. 2). Two LDTs (1, 2 on one side and 3,4 on the other) were attached to the specimens with the purpose of recording diagonal deformations. Other LDTs were used to check the potential rotations of the steel frame on the upper part of the walls (6 and 7) or their relative displacements on the sleigh (5). Eventually, two further vertical LDTs were placed at the bottom of the specimen (8 and 9), aimed to control if relative slips between the concrete of tie beam and masonry would have occurred. Two hydraulic actuators were employed during tests on masonry specimens: a 250 kN horizontal and a 3000 kN vertical one (see Fig. 2). The axial load N was set equal to 10% of the load capacity of the un-strengthened control specimen and maintained constant during the test. Being the average compressive strength of brick masonry equal to 7.62 MPa, and the cross-section dimension to 1310x255 mm 2 , N was 250 kN. Load N was applied in 5 minutes, in force control mode, and two steel profiles were placed on the top of the specimen thus distributing the axial load applied by the actuator on the whole section of the panel. Once the axial load reached the set value, the cyclically reversed horizontal action was applied by imposing a given displacement time history (see Fig.3) to the sleigh on which the wall was placed (see Fig.2).

10 20 30 40

-40 -30 -20 -10 0

0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000

Horizontal displacement [mm]

Time [sec]

Fig. 3. Cyclic test procedure

Three cycles per imposed displacement were performed, by increasing the cycles amplitude of 1 mm up to the last cycle at 20 mm, and then of 2 mm up to the end of test. The velocity rate was also modified during the test as follows: 0.1 mm/s up to the end of 4mm displacement cycles; 0.2 mm/s until the end of 20 mm cycles; 0.5 mm/s till the end. 4. Experimental results This section describes the main information about experimental results, by presenting the failure modes (Fig. 5) and discussing the key features of cyclic response of strengthened masonry walls both in terms of hysteretic cycles (Fig. 4) and skeleton curves (Fig. 4d). 4.1. Strength and ductility Considerations about strength values and ductility are summarized in Table 2, in which behavior attributable to different strengthening methods are compared with results obtained for BM-UR specimen. Experimental results are provided in terms of: peak load values in both directions (F + max and F min ) and corresponding displacement values (s + max and s - min ); displacement values in both directions at 20% strength decay – representing the “conventional collapse” – evaluated on the monotonic force-displacement curves. Furthermore, the increase in ductility due to strengthening at both the peak load ( + / − ) and 20% strength decay ( 0 + . / 8 − ) was evaluated as follows: + / − = + / − + /− (1)