PSI - Issue 44

Fabio Mazza et al. / Procedia Structural Integrity 44 (2023) 1172–1179 F. Mazza / Structural Integrity Procedia 00 (2022) 000–000

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example, the magnitude wavelet coefficient (MWC) of the BI.H ( a Ke =2400) and BI.HV ( a Ke =2000, 800 and 200) structures with a mixed design is shown in Fig. 4. Specifically, spectrograms show frequency content of the Duzce earthquake (see Table 3), with a maximum value of MWC that starts at a predominant period of 0.0979 s for a Ke =2400 (Figure 3a) and shifts at a predominant period of 0.1610 s for a Ke =200 (Figure 3d), also highlighting a significant reduction of MWC that confirms that a good isolation in the vertical direction requires low values of a Ke .

(b)

(a)

(c) (d) Fig. 3. Spectrograms of base-isolated structures with mixed design approach subjected to the Duzce earthquake: (a) BI.H, a Ke =2400; (b) BI.HV, a Ke =2000; (c) BI.HV, a Ke =800; (d) BI.HV, a Ke =200. Finally, the isolation ratio a T (=T 1V,BI.HV /T 1V,BI.H ) in the vertical direction resulting from the wavelet analysis for the selected earthquakes is plotted in Figure 4 as function of stiffness ratio a Ke . Specifically, a reduction target of 50% for the ductility a µ (= µ BI.HV / µ BI.H in Figure 4a) and acceleration a aV (=a V , BI.HV /a V , BI.H in Figure 4b) ratios indicates that the effectiveness of the vertical base-isolation corresponds to a T values greater than 1.7.

(a)

(b) Fig. 4. Vertical isolation ratio for base-isolated structures with mixed design approach.