PSI - Issue 78

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

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Mean of maximum vertical acceleration (a V ), at all levels of the IF structures with (solid curves) and without (dashed curves) vertical base-isolation, are plotted in Figure 2 with reference to the end (blue curves) and mid-span (red curves) sections of beams and in the hypothesis of rigid superstructure (black curves). Results correspond to the beams where MIs are placed (Figure 1), along the X (Figure 2a) and the Y (Figure 2b) directions, respectively. Constant values of a V with the floor levels can be noted when the hypothesis of rigid superstructure is assumed, with slightly greater values for the BIH ( α Ke =2400) structure. On the other hand, increasing values of vertical acceleration are evident along the building height, especially for beams along the Y direction of the BIH structure (Figure 2b). A notable difference between end (blue curves) and mid-span (red curves) sections of beams is also highlightable, for both BIHV ( α Ke =200, solid curves) and BIH ( α Ke =2400, dashed curves) structures. In all cases, greater values of a V are recorded for BIH structure with respect to BIHV one, proving the effectiveness of vertical isolation in reducing vertical acceleration.

(a) X direction. (b) Y direction. Figure 2. Mean of maximum vertical acceleration: BI.IF structures subjected to horizontal and vertical (HV) near-fault ground motions. With reference to the same beams considered in Figure 2, mean of maximum vertical acceleration at the mid-span section of the BI.BF (blue curves) and BI.IF (red curves) structures subjected to the horizontal and vertical component of near-fault ground motions is compared in Figure 3, along the X (Figure 3a) and Y (Figure 3b) directions. To quantify the seismic damage of acceleration-sensitive NSEs lying on the floor, vertical acceleration thresholds for rigid (black dashed lines) and flexible (green dashed lines) NSEs placed along the building height are also evaluated at the LS limit state (Eurocode 8 (2005), Merino et al. (2023)). As expected, constant thresholds are less conservative than linear ones, whose values increase along the building height.

(a) X direction. (b) Y direction. Figure 3. Mean of maximum vertical acceleration at the mid-span section of beams: BI.BF and BI.IF structures subjected to horizontal and vertical (HV) near-fault ground motions.