PSI - Issue 44

Gabriele Guerrini et al. / Procedia Structural Integrity 44 (2023) 2214–2221 Gabriele Guerrini et al. / Structural Integrity Procedia 00 (2022) 000–000

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Fig. 3. Quasi-static cyclic shear-compression test setup.

Since a double-curvature configuration was chosen for the tests, vertical rotation of the pier top was prevented by the implementation of a hybrid control of the vertical actuators: the sum of their forces was kept constant, while imposing the same vertical displacement. Out-of-plane displacements of the pier top were prevented by specific restraints, allowing longitudinal translation only. The specimens were densely instrumented with 39 displacement transducers, mounted on the hidden West face and on the North and South sides, to derive relative and absolute displacements and local deformations. A three dimensional optical motion-capture system was instead employed on the accessible East face: 87 passive retro reflective spherical markers were glued to the specimen surface and were monitored by fixed cameras recording their coordinates as they varied during the tests. Forces were measured by load cells applied to each actuator head. An axial force equal to 25% of the pier compressive strength was desired at its base. Given the pier nominal cross-section of 1.2 x 0.3 m (Fig. 1) and the masonry compressive strength of 1.52 MPa, this corresponded to a force of 137 kN. Subtracting the weights of pier (9.8 kN), top spandrel (7.9 kN), RC spreader beam (12.0 kN), loading steel beam (7.6 kN), and half horizontal actuator (3.5 kN), a combined resultant force of 96.2 kN was applied constantly by the pair of vertical actuators. The horizontal actuator was set in force control and the pier was subjected to three push-and-pull cycles with force amplitude equal to 22 kN for P1 and 27 kN for P2 (about 1/4 of the analytically predicted shear strength) and loading rate of 0.5 kN/s. The following sequence of three cycles had amplitude equal to 1.5 times the previous one, and the same loading rate of 0.5 kN/s. Then, a protocol consisting of displacement-controlled sequences of increasing amplitude was followed. The test was stopped when the specimen presented a potentially dangerous damage or a significant drop of lateral strength, which happened at drift ratios (i.e., lateral displacement normalized by the pier clear height of 1.5 m, Fig. 1) of 3.0% for P1 and 1.75% for P2.

3. Experimental results 3.1. Hysteretic responses

Fig. 4 shows the hysteretic responses of the two specimens together with their envelopes. The lateral displacement was evaluated at the top of the pier and depurated of any sliding measured between the RC spreader