PSI - Issue 44

Maria Maglio et al. / Procedia Structural Integrity 44 (2023) 550–557 M. Maglio, R. Montuori, E. Nastri, V. Piluso / Structural Integrity Procedia 00 (2022) 000–000

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Fig. 4. Pushover curve and collapse mechanism of the structure

5. Conclusion In this work, the design rules for MRFs in DC2 ductility class, which was introduced in the new prEN1998-1-2 (2021), have been reported. The spectrum for the Near Collapse limit state has not been reported because for the new structures, the verification of the non-exceedance of the SD limit state is only required, unless more is requested by an Authority or the national annex. This is because the new prEN1998 draft is such that, for most of the structures, the requirement of non-excess SD implies avoiding the exceeding of NC under seismic action significantly stricter than the design one. It is observed that the reduced SD spectrum is above the service limit state spectra, because the structure factor used is 3.50 which is the maximum that can be assumed for this class. On the other hand, if the behavior factor is larger than 4, the reduced SD spectrum drops below the service limit state spectra. This occurrence can happen in DC3 ductility class where the behavior factor is greater than 3.50. DC2 regards location site with medium seismic intensity, therefore, intermediate design rules have been introduced between the non-dissipative class (DC1) and the very dissipative class (DC3). In particular, the design rules introduced to avoid the soft-storey mechanism (a fundamental requirement to be respected in the DC2 ductility class) presents some criticalities that come both from the initial assumptions and from the final formulation itself. These criticalities, taken as theorems, contradict the scientific literature developed so far in the physical field. Furthermore, fundamental aspects are not taken into consideration such as the contribution of the beams or the effects of the second order, which are important in the case in which a soft-storey mechanism is studied. It is believed that this design rule has been defined in a very elementary way and is not able to ensure the condition for which it was introduced. The numerical application developed confirms the criticisms pointed out in the discussion, in fact the structure collapses because of a storey mechanism which is precisely what the Eq. (11) is intended to avoid. References CEN, prEN1998-1, Eurocode 8, draft, 2021. Design of structures for earthquake resistance - Part 1-1: General rules and seismic action. CEN, prEN1998-2, Eurocode 8 draft, 2021. Design of structures for earthquake resistance - Part 1-2: Rules for new buildings. Montuori, R., Nastri, E., Piluso, V., Pisapia, A., 2020. Ultimate behavior of high-yielding low-hardening aluminum alloy I-beams, Thin-Walled Structures, 146, art. no. 106463. Piluso, V., Pisapia, A., Nastri, E., Montuori, R., 2019. Ultimate resistance and rotation capacity of low yielding high hardening aluminum alloy beams under non-uniform bending, Thin-Walled Structures, 135, 123-136. Piluso, V., Pisapia, A., Castaldo, P., Nastri, E., 2019. Probabilistic Theory of Plastic Mechanism Control for Steel Moment Resisting Frames Structural Safety, 76, 95-107. Montuori, R., Nastri, E., Piluso, V., 2022. Theory of Plastic Mechanism Control: a new approach for the optimization of seismic resistant steel frames, Accepted for publication on Earthquake Engineering and Structural Dynamics. Plumier, A., 2022. Revision of Eurocode 8: Features Common to All Material, in Proceedings of the 10th Interantional Conference on Behaviour of Steel Structures in Seismic Areas, Timisoara. Plumier, A., 2022. Mitigation of soft storey failure: a new criteria, in Proceedings of the 10th Interantional Conference on Behaviour of Steel Structures in Seismic Areas, Timisoara. CEN, Eurocode 1, 2004. Actions on structure Part 1-1: General Actions-Densities, self-weight, imposed loads for buildings.