PSI - Issue 64

Massimiliano Ferraioli et al. / Procedia Structural Integrity 64 (2024) 1025–1032 Ferraioli et al./ Structural Integrity Procedia 00 (2019) 000–000

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Table 1. Demand ( D ) and Capacity ( C ) in terms of PGA and return period ( T r ), Safety index (  ).

Limit State

Combination - F y - e x (Modal) - F y - e x (Uniform) - F y - e x (Modal)

 ( PGA )

 ( T

r )

PGA D 0.102 0.134 0.102

PGA C

T

T

D

C

r

r

Interstorey displacement (IO) Interstorey displacement (DL)

0.090 0.882 0.126 0.940 0.182 1.784 0.237 0.691 0.059 0.172 0.087 0.254

45 75 45

36 67

0.913 0.955

Chord rotation (DL) Chord rotation (LS)

138 1.583 245 0.646

- F x + e y (Uniform) 0.343

712 712 712

- F x + e y (Modal)

0.343 0.343

22 34

0.240 0.287

Beam-column joint failure or RC frames (LS)

Beam-column joint shear failure of RC frames (LS) - F y - e x (Modal)

3. Seismic rehabilitation using orthogonal and parallel dissipative exoskeletons Two alternative retrofitting strategies were considered in this paper: 1) orthogonal exoskeleton equipped with SMA dampers (Fig.2); 2) parallel exoskeleton equipped with steel strip dampers (Fig. 3). The SMA dampers developed by Qiu et al. (2016) are considered that bases on superelastic NiTi wires. The SMA damper (SMADs) (Fig. 4a) comprises two steel rods, two sliding steel blocks, and two sets of NiTi wires experiencing tensile stress under both traction and compression conditions (Fig.4b). U-bolts connect the wire ends within each loop of the NiTi wires. The damper's hysteresis stems from the stress-strain relationship of the NiTi-based SMA wire, enabling it to be represented by a flag-shaped hysteresis (Fig. 4c) loop typical of self-centering devices (Ferraioli et al. , 2019, 2022). This behavior facilitates energy dissipation and complete post-earthquake recovery, even under significant strains, without residual deformations. Among all the other steel strip dampers (SSDs) available in the literature (butterfly, tapered, honeycomb, comb-teeth, hourglass), dumbbell-shaped strip dampers are applied that show significantly improved cumulative ductility and energy dissipation capacity when compared to prismatic strip dampers (Lee et al. , 2015).

c)

a)

b)

Fig. 2. a) Orthogonal dissipative exoskeleton; b) Dissipative Concentric Braced Frame (CBF); c) Details of SMA damper (SMAD).

a)

b)

c)

Fig. 3. a) Parallel dissipative exoskeleton; b) Dissipative Eccentric Braced Frame (EBF); c) Detail of steel strip damper (SSD).