PSI - Issue 78

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

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ACcelerometric Archive v4.0), ensuring spectral compatibility over the period range 0.1–0.8 s. A lower tolerance of 10% and an upper tolerance of 30% were adopted to guide the selection. 4. Comparison between NTC 2018 and FprEN 1998 prescriptions This section presents a comparison between the NLKA prescriptions provided by NTC 2018 and FprEN 1998-3. The procedures used to obtain the capacity curve are essentially the same in both codes, as described in Sections [C8.7.1.2.1.2] and [C8.7.1.2.1.3] of NTC 2018 and Section [11.3.3.3] of FprEN 1998-3. Displacement-based verifications were carried out with respect to the NC limit state for FprEN 1998 and the SLC limit state for NTC 2018, both associated with (near) collapse conditions. While the procedures are similar, minor differences exist, particularly in the coefficients used to determine the period associated with the considered limit state. These are defined in Eq. [C8.7.1.11] of NTC 2018 and Eq. [11.41] of FprEN 1998-3. The main difference between the two codes lies in the formulation of the floor acceleration spectra. It is important to note that both formulations are derived from the same elastic response spectrum defined in NTC 2018 (see Section 3). In NTC 2018, the floor acceleration response spectrum is derived considering a single mode ( i.e. , the first mode) response of the structure ( k = 1), resulting in a modal coefficient of participation equal to 1 = 3 /(2 + 1) with the number of storeys, and 1 = 1. The damping ratio 1 is set at 10%, as specified for NLKA under SLC conditions. The factors and are taken equal to 0.8 and 1.1, respectively. Finally, the spectral acceleration ( , ) corresponds to the elastic response spectrum at the ground floor, as defined in Section 3. The formulation used by FprEN 1998-3 to evaluate the acceleration response spectra for floor j andmode i considers a first-mode response of the structure ( i = 1), using the same expression for the modal participation factor: 1 = 3 /(2 + 1). In the equation, is the number of storeys, and 1 = 1. The period of the ancillary elements ( ) varies from 0 to 2 s, and the associated damping ratio is set equal to 2%. The fundamental period of the primary structure ( ,1 ) is set to 0.1 s, 0.2 s and 0.3 s, depending on the number of floors considered. ,1 is obtained from the elastic response spectrum corresponding to the primary structure. The behaviour factor is introduced to account for the nonlinear response. This factor is equal to 1 for the elastic structure ( EL ) and 1.6 (the maximum value for URM buildings) for the case with limited structural strength (equal to a * = 0.3 g). This was a simple way to account for the plasticity of the structure, especially in everyday engineering practice. A comparison between the EL and limited strength spectra ( a * = 0.3 g) is shown in Fig.3. is the value in the elastic response spectrum which applies to the ancillary element using the damping . Finally, the behaviour factor component ′ , ,1 , which accounts for the deformation capacity and energy dissipation capacity of the ancillary element, was evaluated based on , and ,1 as explained in Clause C.4(1) of FprEN 1998-1-2. The displacement-based verification at the NC limit state in FprEN 1998, when the local mechanism develops at the ground level and level z of the building (Eq. (1) and (2), respectively), shows the contribution of two coefficients that amplify the displacement demand: takes into account the linear-elastic behaviour of the structure under seismic actions; and considers the knowledge level of the structure. These two parameters lead to increased displacement demands compared to those predicted by NTC 2018 for the same limit state, as defined in [C8.7.1.2.1.8]. ( ) ( )≤ / (1) ( )( 2 ) 2 ≤ / (2) 5. Analysis results: Comparison between codified procedures and NLTHA This section compares seismic demands calculated according to the Italian code NTC 2018 and European standard FprEN 1998 with those obtained from NLTHA on SDOF models calibrated using experimental test data. Specifically, comparisons are provided in terms of acceleration response spectra ( S a ) and normalised displacement demands ( θ ) for the local OOP failure mechanism under investigation. 5.1. Elastic ground and floor response spectra Fig. 3 shows the ground design spectrum prescribed by the code along with the corresponding floor acceleration spectra derived as detailed in Sections 3 and 4. It also displays the response spectra of the seven employed GMs