PSI - Issue 78

Salvatore Mottola et al. / Procedia Structural Integrity 78 (2026) 623–630

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The parameters of the idealized nonlinear models of the structure and the exoskeleton are plotted in Tables 1-2, respectively. Table 3 shows the values of the story strength ( V yi ) and stiffness ( K i ) of the exoskeleton, which have to be divided by the number of eccentrically braced frames ( n EB ) in each direction. The plan layout of the EBFs is chosen to mitigate the torsional effects (Fig. 8c). Thus, the story strength and stiffness in the Y-direction are divided equally between the four EBFs (i.e., n EB =4) in the Y-direction, while in the X-direction, the story strength and stiffness of each of the two EBFs in the long side is assumed equal to 1.5 times those of the EBFs in the short side. This gives the target strength ( Q p ) and stiffness ( K y ) of the steel slit damper at each story for each EBF. The aspect ratio ( b p /h p ) of each steel strip is chosen to obtain the desired strength-to-stiffness ratio. The clear length of the strip ( b p ), its thickness ( t ), and the number of strips ( n s ) to be used in each steel slit damper are calculated to reproduce the required stiffness and strength. Tables 4-5 show the design parameters of SSDs. 3.2. Effectiveness of the retrofit strategy The efficacy of the retrofit approach was assessed through nonlinear time-history analyses of the retrofitted building. Seven simultaneously applied accelerograms, representing the horizontal components of the selected ground motion, were used for this analysis. Fig. 9 illustrates the peak inter-story drift ratio (Peak IDR) and absolute acceleration variations for the Collapse Prevention (CP) Limit State. The results, presented for both the X- and Y directions, correspond to four designated columns (A, B, C, and D, as shown in Fig. 9). Comparing the story drift profiles in the X and Y-directions reveals some differences in the distribution of deformations despite similar peak drift magnitudes around 0.75%-0.80%. In the X-direction (Fig. 9a), drifts exhibit a non-uniform distribution, peaking at story 2. Conversely, the Y-direction (Fig. 9b) displays a more uniform drift distribution across stories, indicating a more regular structural response with deformations distributed more evenly along the height. The peak IDR response never exceeds the maximum allowable transient drift taken as 2.0%, corresponding to a typical performance objective for the CP limit state. Fig. 9c-d shows the peak absolute acceleration profile, indicating no significant dynamic amplification along the height. In the X-direction (Fig. 9c), acceleration gradually increases with height, ranging from 0.42g to 0.68g (Fig. 9c), while in the Y-direction (Fig. 9d), it exhibits a nearly constant trend.

h p,1

t

x

Q p

b p

b p,1

e 0 =0

Shear Force

h p,1

Drift Ratio

(a)

(b)

(c)

(d)

Fig. 6. (a) Dissipative EBFs; (b) Steel strip damper (SSD); (c) Geometry of a steel strip; (d) Bilinear idealized elastoplastic model.

0 0.5 1 1.5 2 2.5 00.511.522.533.54 Spectral Acceleration [g] Period [sec] 3A.MZ102 x 3A.MZ102 y IT.NRC.00 x IT.NRC.00 y 230 x 230 y 413 x 413 y 414 x 414 y 600 x 600 y 1703 x 1703 y Average Target

Earthquake name Montenegro

Epicentral Distance [km]

a g,X [m/s²]

a g,Y [m/s²]

N.

EQ.ID

Date

M w

E1 230 E2 413 E3 414 E4 600 E5 1703

24/05/1979 6.2 8.0 13/09/1986 5.9 10.0 13/09/1986 5.9 11.0 12/11/1999 7.2 8.0 30/10/2016 6.6 17.4 30/10/2016 6.6 5.5

1.172 2.624 2.108 2.909 2.354 2.67 1.685 1.041 3.699 5.036 3.652 3.972 4.764 3.651

Kalamata Kalamata

Umbria Marche 26/09/1997 6.0 22.0

Duzce 1

E6 3A.MZ102 Norcia E7 IT.NRC.00 Norcia

Fig. 7. Spectrum compatibility for the CP limit state and parameters of earthquake records.