PSI - Issue 44

Sabatino Di Benedetto et al. / Procedia Structural Integrity 44 (2023) 1901–1908 Di Benedetto et al. / Structural Integrity Procedia 00 (2022) 000 – 000

1907

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shaped joints. These discrepancies are about 30%. These occurrences can also be observed in Table 3, where the main global results are summarized.

Table 3. Comparison between the results of the experimental campaigns RBS FREEDAM

X-shaped T-stub

Base shear (kN)

751 150 3.3 670 171 3.6 555 83 1.8 592 99 2.2 630 129 2.8

537 104 470 112 3.3 347 75 1.7 483 89 2.3 495 112 3

427 166 4.1 572 170 4.1 297 88 2.3 303 109 566 187 4.5 3

Test 1

Roof displacement (mm) Maximum drift (%) Roof displacement (mm) Maximum drift (%) Roof displacement (mm) Maximum drift (%) Roof displacement (mm) Maximum drift (%) Roof displacement (mm) Maximum drift (%) Base shear (kN) Base shear (kN) Base shear (kN) Base shear (kN)

Test 2

Test 3

Test 4

Test 5

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At the local response (Fig. 5), the FREEDAM connections generally exhibit very stable rectangular-shaped moment-rotation hysteretic curves even though no high rotations are achieved. Instead, the RBSs and X-shaped T stubs show a similar response characterized by relevant hardening effects. Nevertheless, the three connection typologies generally dissipate the same energy, as shown in Fig. 5 for connection 1A. Test 5 is also meaningful because it represents the test in which the RBSs failed because of the brittle fracture of some welds and a reduced section, while the structure with FREEDAM and dissipative double-split tee joints did not reach the collapse. Obviously, the previous comparisons concerning Test 5 have been carried out only in the time range before the crisis of the RBSs. For clarity, Test 5 in all the campaigns ended at 8.58 s of the Coalinga earthquake. The final configurations displayed by the joints at the end of the campaigns are reported in Fig. 6. The fractures in the welds and the reduced section of the RBSs are evident in Fig. 6. In particular, the local collapse of the joints can be ascribed to the achievement of the fatigue life of the welding and the unexpectedly high bending moment acting at the column flange level. Concerning the FREEDAM connection, minor yielding occurred in the stem of the bolted T-stub close to the centre of rotation. Similar minor yielding occurred in the friction damper's angles to the column flange. The energy dissipation is concentrated in the friction shims, as shown by the scratches (Fig. 6) due to the sliding of the friction pads. Finally, the deformed configuration of an hourglass T-stub is reported in Fig. 6, which highlights that the only dissipative and damaged element is the X-shaped T-stub, as expected. At the end of all the experimental campaigns, the column bases' yielding was observed.

Fig. 6. Crisis of RBS connections 1A (left), damaged friction pad (centre), deformed dissipative double split 1A joint (right)