PSI - Issue 44

Alessandra Gubana et al. / Procedia Structural Integrity 44 (2023) 512–519

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A. Gubana and A. Mazelli / Structural Integrity Procedia 00 (2022) 000–000

(CNR DT 212/2013). A Rayleigh damping at 5% was set, and the P-Delta effects were neglected, on the basis of preliminary IDAs (a maximum difference of 0.02% on the IDRs with and without P-Delta).

Fig. 5. Average acceleration response spectrum of the input motions compared to the code Life Safety spectrum.

IDAs were performed in single directions (X, Y, +45° and -45°) and in X and Y simultaneously. For seek of brevity, only the bidirectional results have been reported in Fig. 6.

Fig. 6. IDA curves for PGA (a) and S a (T 1 ) (b).

Fig. 6a shows the IDA curves for the PGA choice, and Fig. 6b the curves for the S a (T 1 ) case. A coloured dot signals the threshold corresponding to a DL (Green – DL1, Yellow – DL2, Orange – DL3, Red – DL4-5). The analyses were pushed to high value of IDR, in order to investigate local collapse phenomena. Due to simplification and to the absence of strength degradation in fibre hinges, the FEM model was not able to catch the so called “dynamic instability”. 5. Fragility Curves FCs are the graphical representation of the probability of exceeding a predefined level of damage. In this work, the development of the FCs followed the CNR-DT 212 (2013) indications. The probability of exceeding a damage state Y conditioned on a measure of the seismic intensity S=s is reported in formulation (1). !" ( ) = ( !" ≥ 1| = ) = + # !" $% ≤ - = / &' ()* #$ ! %&' + #$ ! %&' 0 (1) where Φ is the standard normal cumulative distribution function, s is the selected IM, and μ lnS Y =1 σ lnS Y =1 are the mean and the standard deviation of the logarithm of the intensity S Y =1 that induces the specified damage level.