PSI - Issue 44

P. Morandi et al. / Procedia Structural Integrity 44 (2023) 1060–1067 Author name / Structural Integrity Procedia 00 (2022) 000–000

1062

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Regarding the testing protocol, the tests started with an initial force-controlled phase, followed by displacement controlled cycles, in which programmed displacements with increased amplitudes have been cyclically imposed in both directions, up to the attainment of ultimate conditions of the specimens; at each level of force/displacement amplitude three cycles were performed, as usually done in similar experimental tests in the past (see Morandi et al. 2018). The test set-up, the instrumentation, and the testing protocol are described in more detail in Manzini et al. 2022. As already stated in the previous section, only two solid brick masonry specimens, among the tested ones, are considered in this paper. Specifically, a squat unreinforced specimen and the corresponding strengthened one, with the same mechanical and geometrical properties, were tested in double-fixed boundary conditions and with a realistic value of vertical stress (on this topic, refer to Morandi et al. 2021), in order to achieve a shear failure, according to the predictions with relevant codified formulations (more information on this issue can be found in Albanesi and Morandi 2021). The nominal pier dimensions, the vertical stress level, and the boundary conditions for the considered walls are summarized in Table 1, as well as the failure mode. Fig.1 shows the pictures of the tested specimens and some details of the basic module of the installed retrofit system.

Table 1. Considered masonry walls subjected to cyclic in-plane tests.

Failure mode

Reinforcement l (mm)

t (mm)

h (mm) σ v (MPa) σ v / fc m (%) Boundary conditions

Specimen Masonry typology

UBPS01 RBPS01

Brick Brick

No

2330 2330

250 250

2435 2435

0.50 0.50

7.1 7.1

Double fixed Double fixed

Shear Shear

Yes

a)

b)

c)

Fig. 1. Experimental quasi-static in-plane tests: a) unreinforced specimen UBPS01; b) retrofitted specimen RBPS01; c) retrofit module details.

The experimental hysteretic curves and the related global force-displacement envelopes for the considered tests are reported in Fig. 2; the cycles at each target displacement value are represented in grey, while the global envelope curve is marked with a black line. As expected, the two specimens UBPS01 and RBPS01 exhibited a crack pattern typical of shear failures, characterized by bi-diagonal cracks spreading from corner to corner of the pier. In both walls cracks were mainly located in the mortar bed- and head-joints with a limited extent in the clay bricks. The shear damage started developing from a drift ratio ( θ = δ / h ) of 0.10% for the specimen UBPS01 while at θ = 0.15% in specimen RBPS01. In both the experimental tests, the shear cracks grew in number and width with the increase of the lateral displacement amplitude, thus leading to a progressive reduction of the lateral strength and stiffness of the specimens up to their ultimate conditions. The tests were stopped to prevent the collapse, at θ = 0.25% for pier UBPS01 and at θ = 1.00% in the case of the retrofitted pier RBPS01. As it is possible to observe from Fig.2, the retrofit system allowed the specimen to increase by four times its ultimate displacement capacity, without affecting the