PSI - Issue 64

Maria Ntina et al. / Procedia Structural Integrity 64 (2024) 2036–2043 Maria Ntina/ Structural Integrity Procedia 00 (2019) 000–000

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displacement reduction while the steel scheme showed no reduction except of the X-direction for Northridge earthquake. Maximum and residual displacement reduction reveals the SMA re-centering and energy dissipation properties. Having a modulus of elasticity lower than the 20% of that of steel, the stiffness of the structure is not enhanced, as in the case of steel retrofit. Top X-axis and Y-axis displacement time histories under Athens earthquake (Figs 5 and 6) depict the lower stiffness of structures with the SMA schemes compared with the structure with the steel scheme, as a deviation from the horizontal axis is observed. Response reduction is achieved through the re-centering and energy-dissipation properties. Another interesting remark is that single-crystal Cu-based SMAs, having lower transformation stresses and modulus of elasticity but larger superelastic strain, exhibited a superelastic behavior comparable to Ni-Ti SMAs. The recent development of Cu-Al-Mn alloy manufacturing processes that allow the production at low cost (Mazzer et al, 2019) addresses the issue of cost-efficiency as one of the main challenges of using SMAs in engineering applications is their high cost compared to traditional steel reinforcement.

Table 2. Main data of selected earthquakes. Earthquake / Location / Year

Magnitude (Mw)

Recording Station

Athens Kozani

6.70 6.60 6.50 7.51

KORA KOZ1 AIGA

Aigio

Kocaeli/Izmit Turkey/1999

YARIMKA KOERI

Gilroy Array #3, 090 GDMG Station 47381 Castraic-Old Ridge Route, 090 CDMG Station 24278

Loma Prieta / CA USA / 1989

6.93

Northridge / CA USA / 1994

6.69

Table 3. Maximum displacements.

Initial structure (m)

Steel retrofit (m) 0.0956 0.0073 0.0745 0.0048 0.1031 0.0204 0.0317 0.0035 0.0459 0.0055 0.0459 0.0109

NiTi retrofit (m) 0.1244 0.0107 0.1214 0.0073 0.1184 0.0216 0.0325 0.0034 0.0525 0.0053 0.0238 0.0126

CuAlMn retrofit (m)

CuAlBe retrofit (m) 0.1362 0.0107 0.1265 0.0078 0.1371 0.0273 0.0294 0.0033 0.0543 0.0053 0.0558 0.0108

Earthquake Record

% Reduction

% Reduction

% Reduction

% Reduction

Direction

Athens Athens Kozani Kozani

X Y X Y X Y X Y X Y X Y

0.2109 0.0169 0.1909 0.0065 0.1917 0.0376 0.0486 0.0057 0.0763 0.0057 0.0729 0.0158

55% 57% 61% 26% 46% 46% 35% 39%

41% 37% 36% 38% 43% 33% 40%

0.1254 0.0086 0.1229 0.0076 0.1220 0.0278 0.0293 0.0033 0.0534 0.0053 0.0536 0.0115

41% 49% 36% 36% 26% 40% 42%

35% 37% 34% 28% 27% 40% 42%

Increase

Increase

Increase

Aigio Aigio

Kocaeli Kocaeli

Loma Prieta Loma Prieta Northridge Northridge

40%

31%

30%

29%

4%

7%

7%

7%

37% 31%

67% 20%

26% 27%

23% 32%

Table 4. Residual displacements.

Initial structure (m) 0.05984 0.00376

Steel retrofit (m) 0.04803 0.00240

NiTi retrofit (m)

CuAlMn retrofit (m) 0.01736 0.00198

CuAlBe retrofit (m) 0.05434 0.00041

Earthquake Record

% Reduction

% Reduction

% Reduction

% Reduction

Direction

Athens Athens

X Y

20% 36%

0.09564 Increase

71% 47%

9%

0.00297 21%

89%