PSI - Issue 44

Brandonisio Giuseppe et al. / Procedia Structural Integrity 44 (2023) 1292–1299 Giuseppe Brandonisio et al. / Structural Integrity Procedia 00 (2022) 000–000

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Fig. 9. Comparison between spectral accelerations of model 1 (current state) and model 2 (final design solution).

Fig.10. Shear force distribution at the base of cross walls in Model 3 – seismic input acting longitudinally (left) and transversally (right).

Fig.11. Shear force distribution at the base of cross walls in Model 4 – seismic input acting longitudinally (left) and transversally (right).

It is clear that that the dimensionless shear force at the base, obtained dividing it by the seismic weight, F/W, decreases from about 25% of the model 3 to 3.5% of the model 4, corresponding to a reduction of the seismic actions of one order of magnitude. In the model 3, the shear force at the base, in longitudinal and transversal directions (Fig.10), is bear by shear walls to the extent of 90%, with a resulting reduction of the seismic demand on the original structure. In the model 4, the shear force at the base is filtered by the isolation system in transversal direction (Fig. 11 – left) and it is absorbed by the shear walls being parallel to the force direction, while the original structure results not excited by seismic action. In the model 4, the shear force at the base is filtered by the isolation system in longitudinal direction (Fig. 11 – right); the 50% is bear by the shear walls being parallel to the force direction, while the remaining 50%, equal to 160t and corresponding to a low F-to-W ratio of 1.85%, is absorbed by the transversal cross walls and by the frames of the original structure.