PSI - Issue 64

E. Choi et al. / Procedia Structural Integrity 64 (2024) 2028–2035 Eunsoo Choi / Structural Integrity Procedia 00 (2019) 000 – 000

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Table 1. Summary of specific values Specimen notation Peak force (kN)

Ductility factor Push 3.94

Drift at peak (%)

Drift at yield (%)

Drift at failure (%)

Push 126.8

Pull 125

Push

Pull 2.0

Push 1.11

Pull 1.04

Push 4.37

Pull 4.21

Pull 4.02

RC-Ref average

2.5

125.9

2.25

1.075

4.29

3.98

RC-SMA-N

94.7

106.1

5.0 6.0

7.0

0.79

0.46

7.5 7.5

7.5

9.51

16.3

Average

100.4

0.625

12.91

RC-SMA-H

80.1

92.3

5.25

5.25

0.87

0.72

7.49

7.51

8.59

10.41

average

86.2

5.25

0.795

7.5

9.5

Lateral load-displacement responses

The steel reinforcement in the conventional RC column of RC-Ref yielded at a drift ratio of 1.075%, with a lateral force of 108 kN and a peak force of 125.9 kN at a drift ratio of 2.25 %. However, the RC-SMA-N specimen exhibited a yield drift ratio of 0.625% with a 63 kN lateral force. The early yield drift ratio of the RC-SMA-N specimen appeared to be caused by the concentration of curvature at the coupler connection zone. The steel rebar at the coupler yielded earlier owing to its large curvature. The lower yield force of the RC-SMA-N specimen could be attributed to the lower axial rigidity and large elastic strain range of the SMA rod. The SMA rod provided relatively small resistance to the yielding of the steel rebar because of its relatively small axial rigidity. The failure point of RC-Ref was 4.29%, whereas that of RC-SMA-N was > 7.5%. Thus, the RC-SMA-N specimen exhibited almost twice the ductility. The RC-SMA-N column exhibited completely different hysteretic loops compared with those of a conventional RC column (Figure 7). The column exhibited initially high stiff behavior with small cracking ( Ⓐ state in Figure 7). Then, with increasing cracking, the loading stiffness decreased accompanied by rocking action at Ⓑ state, as shown in Figure 7. As the cracks increased, the loading stiffness decreased and the rocking action appeared clearly, but the flexural strength did not decrease ( Ⓒ state in Figure 7). However, the crushing of concrete slightly decreased the flexural strength ( Ⓓ state); thus, it is inferred that the flexural strength decreased as concrete crushing increased, reaching the failure point.

Drift ratio (%)

-9-7-5-4-2 0 2 4 5 7 9

C D

100

B

A

50

0

Load (kN)

-50

-100

-125 -100 -75 -50 -25 0 25 50 75 100 125

Displacement (mm)

Figure 7. Hysteretic loops of the RC-SMA-N specimen with intervals

Self-centering and energy dissipation capacities One of the main goals of this study was to investigate the effects of martensitic SMA bars on the self-centering capacity of an RC column in comparison with a conventional one. Thus, this study first estimated the residual drift versus the maximum applied drift. Figure 8(a) shows the result of the pushing action. Figure 8(b) shows the displacement recovery ratio (DRR), which is calculated by dividing the residual drift by the maximum applied drift and indicates