PSI - Issue 78

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

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As can be observed, the NSEs thresholds for rigid and flexible elements are generally exceeded for the BF and IF structures along the Y direction (Figure 3b), especially when horizontal base-isolation (i.e. α Ke =2400) is considered. On the other hand, the NSE threshold for flexible elements can be assumed as conservative only when horizontal and vertical base-isolation (i.e. α Ke =200) is assumed. Moreover, the vertical acceleration at the centre of gravity of MIs arranged along the X (Figure 4a) and Y (Figure 4b) directions is plotted for the BI.IF structures subjected to the horizontal (H, blue curves) and horizontal and vertical (HV, red curves) component of near-fault ground motions. Differently from the mid-span section of beams, thresholds for NSEs hanging from MIs are usually satisfied for both rigid and flexible elements, only with some exception at the higher levels when the vertical component of near-fault earthquakes is considered.

(a) X direction. (b) Y direction. Figure 4. Mean of maximum vertical acceleration at the centre of gravity of MIs: BI.IF structures subjected to horizontal (H) and horizontal and vertical (HV) near-fault ground motions. Afterwards, the mean of maximum vertical acceleration at the top floor is reported in Figure 5 with reference to the mid-span section of beams and the IF configuration. Specifically, results for the BIH and BIHV structures are reported for central (Figure 5a) and perimeter (Figure 5b) bays of frames along the Y direction. As a confirmation, the horizontal and vertical base isolation (BIHV) proves to be very effective, reducing the acceleration demand by half in comparison to the horizontal one (BIH). It is interesting to note that significant differences are observed when mid-span sections of the perimeter frame are examined (Figure 5b), while only slight differences are recorded among external (black dot), internal (red dot) and central (blue dot) beams (Figure 5a).

(a) Central bays of frames along the Y direction. (b) Perimeter bays of frames along the Y direction. Figure 5. Mean of maximum vertical acceleration at the mid-span section of beams at the top floor: IF structures with horizontal (BIH) and horizontal and vertical (BIHV) base-isolation (unit in m/s 2 ).