PSI - Issue 78

Marta Bertassi et al. / Procedia Structural Integrity 78 (2026) 1521–1528

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(individually, as well as their mean) estimated from NLTHAs on linear-elastic and nonlinear ( i.e. , with limited lateral strength) SDOF oscillators. In Fig. 3, it is readily apparent that the floor spectra are consistent with the NLTHA results for elastic structures ( EL ). A slight underestimation of the peak spectral ordinates is noticeable in the case of NTC 2018, while FprEN 1998 tends to overestimate them. For structures with limited strength ( a * = 0.3 g), NTC 2018 tends to overestimate the spectral demand for periods shorter than T 1 and underestimate it for periods longer than T 1 . In contrast, the FprEN 1998 tends to overestimate the spectral ordinates only for periods shorter than T D . It is noticeable that, unlike the FprEN 1998, the NTC 2018 elastic ( i.e. , EL ) and inelastic ( i.e. , a * = 0.3 g) spectra formulations are identical, as the Italian building code does not explicitly account for a floor spectral reduction factor in the calculation.

Fig. 3. Response spectra of the seven GM records used for NLTHA, along with floor acceleration spectra computed at three floor levels using linear and nonlinear SDOF models. Comparison with the elastic design spectra and corresponding floor spectra according to NTC 2018 and FprEN 1998. 5.2. Displacement demands Figs. 4 to 6 compare the displacement demands obtained by applying the codified NLKA procedures ( θ codes ) with those predicted by NLTHAs ( θ NLTHA ). In the plots, displacements are normalized by the wall thickness.