GNGTS 2022 - Atti del 40° Convegno Nazionale

GNGTS 2022 Sessione 2.2 255 ASSESSMENT OF THE EFFECT OF SEISMIC SEQUENCES ON STEEL X-CBF FOR INDUSTRIAL BUILDINGS L. Bomben, M. Fasan, C. Amadio University of Trieste, Department of Engineering and Architecture, Trieste, Italy Background. It is known that earthquakes are not in general isolated events, but they can be followed by several after-shocks, that can have a comparable intensity to the main- shock. In fact, Ruiz Garcia in (Ruiz Garcia, 2014) underlined that, although the main-shock is always the event with the maximum magnitude, in a specific site an after-shock can have a higher PGA. This fact can lead to a progressive accumulation of damage, if the time span between the events is not enough to repair the structure. Current technical codes (British Standards Institution et al. , 2005; Ministero delle infrastrutture e dei trasporti, 2018) do not take into account the effect of the seismic sequences, thus the structures are designed only to withstand a single event. Several past studies have already investigated on the effect of the seismic sequences on steel structures (Amadio et al. , 2003; Fragiacomo et al. , 2004; Hatzigeorgiou, 2010; Rinaldin et al. , 2020, 2017; Ruiz Garcia and Negrete-Manriquez, 2011), by evaluating both single-degree- of-freedom (SDOF) and multi-degree-of-freedom (MDOF) systems. Both moment resisting frames (MRF) and concentrically braced frames (CBF) have been analyzed, proving the great influence of the sequences to these structural types. Other studies, like in (Iervolino et al. , 2014; Lolli and Gasperini, 2003), are focused on the influence of the seismic sequences on the seismic hazard evaluation. The present work concerns about the study of the effects of the seismic sequences on the design of mono-storey industrial buildings with X–concentrically braced frames (X-CBFs). First, a typical mono-story industrial building is analyzed (Section 2), subjected to natural seismic sequences. Then, the study focuses on the behavior of X – concentrically braced frames (Section 3), by considering both natural and artificial repeated ground shakings. A proper enlargement of the elastic response spectra is finally proposed, representative of the sequences effects and applicable on medium-high seismicity areas. This operation wants to give a first preliminary estimate of the increase of the seismic risk only on the seismic vulnerability side of this kind of structures. Preliminary case study. The industrial steel building with X-CBFs designed by Scozzese et al. (ReLUIS et al. , 2018; Scozzese et al. , 2017), according to (Ministero delle infrastrutture e dei trasporti, 2008) and located in L’Aquila (Italy), has been analyzed as preliminary case study (Figure 1.a). The structure has been modeled with Seismostruct (Seismosoft, 2020), that considers a fiber approach to model the inelastic behavior of the elements, according to a force-based finite element formulation. The Menegotto-Pinto model (Menegotto and Pinto, 1973) has been chosen to represent the uniaxial stress-strain relationship of steel. With the aim to validate the model, a series of pushover analysis on the whole structure have been carried out and calculation of the braces buckling strength has been done (according to the relationships given in (British Standards Institution et al. , 2005)). The results have shown a great correspondence with the ones given in (ReLUIS et al. , 2018). The system has been subjected to nonlinear dynamic analysis, through the application of both seismic sequences and the main shock (single events with maximum PGA). A series of relevant sequences of Italy and Japan has been selected. The events constituting the sequences have been obtained through the Engineering Strong Motion Database (INGV), for the Italian events, and Strong-motion seismograph networks (K-NET, KiK-net) for the Japanese ones. The sequences have been composed with MATLAB letting 30 seconds of rest between subsequent events, in order to completely stop the structure. In total, 40 seismic sequences have been