PSI - Issue 78

Fabio Mazza et al. / Procedia Structural Integrity 78 (2026) 33–40

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Finally, time histories of vertical acceleration at the mid-span section of the central beam of the perimeter Y frame at the top floor are post-processed to evaluate dominant frequencies and the maximum wavelet transform coefficient (WTC). To this end, a homemade MATLAB (MATLAB (2018)) computer code is implemented using the continuous wavelet transform in combination to the complex Morlet wavelet (Mazza et al. (2024a)). Specifically, spectrograms are shown for bare (BF, Figures 6a,c) and infilled (IF, Figure 6b,d) structures, with (BIHV, Figures 6a,b) and without (BIH, Figures 6c,d) vertical base-isolation, subjected to the DSLC station of the Darfield near-fault earthquake. In particular, a significant increase of the maximum WTC value is evident when BIH structures are examined in the infilled configuration (Figure 6d). As expected, the increase of the fundamental vibration period for the BIHV structure induces a significant reduction of WTC shifting backward in time (Figures 6a,b)

(a) BIHV.BF ( α Ke =200).

(b) BIHV.IF ( α Ke =200).

(c) BIH.BF ( α Ke =2400). (d) BIH.IF ( α Ke =2400). Figure 6. Spectrograms of BIHV.BF (a), BIHV.IF (b), BIH.BF (c) and BIH.IF (d) structures subjected to Darfield earthquake (station DSLC).

5. Conclusions Impact of the vertical component of near-fault earthquakes on the nonlinear response of RC structures with (BIHV) and without (BIH) vertical base-isolation, in terms of vertical acceleration on structural frame members and rigid and flexible nonstructural elements (NSEs) lying on the floors and hanging from MIs, is the aim of this work. To this end, an existing five-storey hospital building in Avellino (Italy), retrofitted with a double base-isolation system, is adopted as test structure. An in-series vertical combination of a high-damping rubber bearing (HDRB) and high-damping rubber layers (HDRLs) is considered, the latter independent on the horizontal and vertical (in tension) responses of the HDRB. The following conclusions can be drawn briefly from the results of nonlinear dynamic and wavelet analyses carried out considering bare and infilled structures, the latter taking into account the IP-OOP nonlinear behaviour of