PSI - Issue 44

Paolino Cassese et al. / Procedia Structural Integrity 44 (2023) 774–781 P. Cassese et al. / Structural Integrity Procedia 00 (2022) 000 – 000

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Starting from set VI, the lateral resistance of the panel decreased with pronounced spalling of the concrete in the lower corners of the wall. Specimen W1 experienced mechanical failure during set VI, corresponding to an IDR of 0.87%. Furthermore, there was evidence of concrete spalling along the wall/foundation interface associated to rigid body sliding and fixed-end rotation of the wall. On the analogy with specimen W1, the wall W2 showed cracking onset during set I. First yielding had place during set III, as identified by SG records and confirmed by a subtle peeling observable in the lower corners of the panel. This set (IDR = 0.40%) corresponded to the maximum strength equal to 338.3 kN (push) and 324.5 kN (pull). Starting from set IV, softening phase developed with a gradual reduction of the load-bearing capacity of the structural member. The conventional failure of the specimen occurred during the set VI, when extended damage at wall/foundation interface was observed due to sliding. The test was stopped at IDR equal to 1.30% (set VII) when a considerable reduction of lateral resistance was observed. 3.3 Comparison of the response of cRCSPs Displacement and force values of characteristic points of the mechanical behavior (i.e., cracking, yielding, maximum and ultimate strength conditions) are summarized in Table 1 for each specimen. Generally, an approximately symmetrical behavior can be observed, with some slight variations: the specimens presented a fairly higher capacity in push with respect to pull basically because loading cycles started along the push direction. As known, axial load levels influence the mechanical response of structural elements (Paulay & Priestley, 1992): higher values of axial load are commonly associated with increasing lateral load resistance and reduction of the ductility of the element (Looi et al., 2017). This behavior was confirmed by test results. Particularly, the results associated with panels O showed that the panel O1 experienced onset of yielding during the first cycle of set II (IDR=0.2%), whilst the panel O2 required an IDR of 0.4% for starting the yielding process, i.e., during the set III. Similarly, panels W1 and W2 started their yielding processes during sets II and III, respectively. Furthermore, with a change from 50 kN to 100 kN of the axial load of element O2 with respect to element O1, there was also an increase in the maximum force capacity of 15%. Conversely, the ductility capacity, herein assumed as the ratio of the failure displacement to the displacement associated with yielding of outer steel bars (i.e., first yielding condition), of the specimen O2 was reduced by 48%. At the same time, panel W2 exhibited a maximum force increase of 8% and a 13% reduction of ductility. A negligible influence of axial load variation on the displacement corresponding to the peak condition was observed: both W- specimens reached their maximum resisting force at IDR equal to 0.4% and both the O- panels at 0.6% IDR. All tested specimens evidenced responses with a pinching characteristic. In the case of O- panels, it was mainly associated with flexure-shear deformation mechanisms, whereas for W- specimens, considerable sliding was observed. Regarding damage states, significant flexure-shear interaction characterized all the specimens, with several diagonal cracks. W- specimens presented greater evidence of damage at the base, related to the damage generated by sliding and fixed-end rotation effects at the base.

Table 1. Critical points of the mechanical response.

Cracking

Yielding

Maximum

Ultimate

Panel

Disp [mm]

Force [kN]

Disp [mm]

Force [kN]

Disp [mm]

Force [kN]

Disp [mm]

Force [kN]

O1 O2 W1 W2

2.90 2.87 2.86 2.85

94.15 100.81 192.79 203.07

6.60 10.44 6.71 7.11

152.80 214.06 275.65 288.55

17.24 17.25 11.43 11.42

237.52 267.30 308.12 331.37

29.15 26.78 24.82 29.77

190.02 213.84 246.50 265.09

Conclusions The seismic performance of four cRCSPs was experimentally assessed in this study. Different aspect ratios, axial load levels and configurations (with and without door-type opening) were considered. Relevant experimental outcomes are listed below. • Cracking onset was observed since the first loading step, corresponding to IDR values lower than 0.1%, for all specimens. • The significant influence of the applied axial load level on the mechanical response of the panels was experimentally confirmed: (i) specimen O2, identical to O1 but with twice the axial load level applied to