PSI - Issue 44

Samuel Barattucci et al. / Procedia Structural Integrity 44 (2023) 426–433 Barattucci et al/ Structural Integrity Procedia 00 (2022) 000–000

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3.2. Experimental setup and test protocol The setup was specifically designed to carry out the coupled axial-shear cyclic test on r.c. frame. The designed setup used the facilities of the CIRI-EC structural testing laboratory: the infilled r.c. frame system was anchored to the strong floor while the horizontal thrust was imposed on the top r.c. beam by means of 500 kN MTS servo-hydraulic jack properly anchored to the concrete reaction wall. The infilled r.c. frame was anchored to the strong floor by means of rigid steel brackets and post-tensioned dywidag bars in order to avoid any possible horizontal sliding of the base beam. The steel brackets aligned on the r.c. columns also served as fastening system for the vertical bars used to apply the axial force to the columns. During the tests, a constant axial load of 250 kN was applied to each column by means of hydraulic jacks placed on top of them and constrained by transverse steel beams, fastened to the bottom brackets described before. The vertical load application system was designed with rod end pins and conical nuts, that allowed cyclic large displacements along the horizontal direction. The horizontal thrust application system was composed by a steel tie made up of stiffened transverse steel plates placed at the ends of the upper r.c. beam and connected through post-tensioned dywidag bars. The servo-hydraulic actuator generating the cyclic force was connected to one end of the tie and was constrained to the reaction wall. The entire test system was transversally stabilized by means of a specifically designed lattice steel system allowing for the horizontal and vertical displacements only of the top r.c. beam through ball rollers. This transverse stabilization system avoided possible out of plane displacement of the r.c. frame due to the eccentrical masonry infill. Figure 2 shows a comprehensive scheme of the setup and the photo of the specimen. Table 1 summarizes the instruments used, while their placement on the tested r.c. frame is illustrated in Figure 2. Two steps loading protocol was used for all the experimental tests carried out: Step 1 – monotonic application of target axial load of 250 kN to the r.c. frame columns; the load was kept constant for the entire duration of the tests, by controlling the hydraulic jacks pressure; Step 2 – cyclic application of horizontal displacement to the upper beam of the r.c. frame: during this phase horizontal drift cycles of increasing amplitude were applied by controlling the

Fig. 2. Experimental setup

Table 1. Instruments used during the test. Instrument ID

Position

Type

Capacity

A

Upper beam Upper beam

Actuator + Load cell

± 500 kN, ± 250 mm

P1 P2

Potentiometer Potentiometer Wire instrument Wire instrument

250 mm 50 mm 300 mm 300 mm

Foundation beam Diagonal Nodes 1-4 Diagonal Nodes 2-3

WIRE 1-4 WIRE 2-3