PSI - Issue 62

Stefano Stacul et al. / Procedia Structural Integrity 62 (2024) 617–624 Stefano Stacul and Nunziante Squeglia / Structural Integrity Procedia 00 (2019) 000 – 000

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7

Fig. 7. Comparison between KIN SP, fixed-base SDOF and compliant-base SDOF results (SRA analysis results were used as input)

Let us now consider the case in which in the use of the two simplified systems (fixed-base and compliant-base SDOF) the evaluation of the maximum acceleration of the superstructure (SDOF) is made by directly exploiting the Ground Types C and D spectra according to NTC (2018) and assuming a fundamental period of the SDOF equal to T fixed (i.e., 0.6 s) and T SSI (according to the semi-empirical relation of Gazetas (1996) in Equation 6) for the fixed-base model and the compliant base model, respectively. In Equation 6 k s and h s are the stiffness and height of the SDOF, while K L , K C and K R the swaying, the coupled rocking-swaying and the rocking stiffness of the foundation, respectively. It is clear, looking at Figure 8, that in all the cases, with the only exception of the Ground Type C, the simplified approaches lead to a general overestimation of the SDOF maximum acceleration compared to KIN SP.

s + + + s k k h

k

2

1

SSI T T =

h

s

(6)

fixed

s

s

K K K

L

C

R

Fig. 8. Comparison between KIN SP, fixed-base SDOF and compliant-base SDOF results. (KIN SP results are based on advanced SRA)