GNGTS 2021 - Atti del 39° Convegno Nazionale

263 GNGTS 2021 S essione 2.2 Considering this connection typology, nine case-studies buildings with a different number of storeys ( i.e., 4, 6 and 8) and bays ( i.e., 5, 7 and 10) are designed according to Eurocode 8 [3] and modelled in OpenSees [4] to investigate the influence of the frame layout on their seismic performances. The plan and the elevation views of the case-study frames are shown in Fig 2(a) and (b), respectively. The horizontal resisting system is composed by perimeter MRFs, while the interior part is composed of gravity frames ( i.e., with ‘pinned’ beam-to-column connections and ‘pinned’ column bases). Two configurations are analysed and compared for each case-study: the first is the ‘equivalent’ MRF with conventional full-strength column bases, the second is the MRF including the self-centring column base connections. Beam-to-column connections are conventional full-strength rigid joints. The Type 1 elastic response spectrum with a peak ground acceleration equal to 0.35g and soil type C is considered for the definition of the Design-Based Earthquake ( i.e. , DBE, probability of exceedance of 10% in 50 years, Ultimate Limit State according to the European definition). The Maximum Credible Earthquake ( i.e. , MCE, Collapse Limit State according to the European definition) is assumed to have an intensity equal to 150% the DBE. Incremental Dynamic Analyses (IDAs) [5] are performed with a set of 30 ground motion records while monitoring both global and storey-level engineering demand parameters, including peak and residual interstorey drifts. Fragility curves [6]are successively used to provide a probabilistic interpretation of the results and of the sensitivity of the seismic response with respect to the frame layout, giving insights on the self-centring capability, and hence the reparability of the structures. Fragility curves provide the probability of exceeding the assumed residual interstorey drifts capacity value ( i.e., probability of failure P f ) vs the seismic intensity measure values. Global and storey-level residual response parameters ( i.e., the maximum residual interstorey drifts and the storey-level residual interstorey drifts) are considered as engineering demand parameters (EDPs). These values are compared with the associated capacity threshold which is conventionally assumed as 0.5% [7]. The comparison of the global fragility curves ( i.e., maximum residual interstorey drifts among all the storeys as engineering demand parameter) is shown in Fig 3 for all the case-studies for the two configurations ( i.e., with and without the self-centring damage-free column base connections). The maximum (among all the storeys) residual interstorey drifts is used as EDPs. Additionally, the percentage reductions of the probability of exceeding the limit value ( i.e., Δ P f ) are also reported for the two seismic intensities of interest ( i.e., DBE and MCE). In Fig 3 it is possible to point out that the Δ P f decreases with the increasing height of the case-studies, while it is not possible to observe a significant sensitivity to the variation of the number of bays on Fig. 2 - Case-study buildings: (a) Plan views; (b) Elevation views.