PSI - Issue 44

Giuseppe Brandonisio et al. / Procedia Structural Integrity 44 (2023) 1316–1323 Giuseppe Brandonisio et al. / Structural Integrity Procedia 00 (2022) 000–000

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At the current state, the shear walls distribution is highly asymmetric in plan: these elements are the only ones with a certain horizontal stiffness at the second and third levels. Additional two shear walls have been introduced to regularize the stiffness distribution in the plan (see Fig.6). It is also necessary cut the shear walls below the floating plane to ensure the functioning of the isolation system. In particular, this hybrid solution requires the use of BIS, made of 32 HDRBs ( f 600 mm) and 8 steel-teflon sliders, as visible in Fig. 6. These anti-seismic devices will stand below the steel beams of the floating plane. This solution leads to a considerably increasing of the vibration period, as discussed below. 4.1 Structural analyses of the retrofitted building and comparison with the AS-IS configuration To evaluate the effectiveness of this hybrid retrofit, the dynamic characteristics of the as-is and retrofitted models are compared in Fig.7, Fig. 8, and Fig. 9.

Fig. 7. Comparison between dynamic characteristics of the models- 1 st vibration mode: (a) Fixed base; (b) Isolated

Fig. 8. Comparison between dynamic characteristics of models- 2 nd vibration mode: (a) Fixed base; (b) Isolated

In detail, from Fig. 7, it is visible that the fundamental period of the structure at the current state, Fig. 7 (a), T 1 =0.563 s, increases to T 1 =3.05 s with the introduction of BIS, Fig. 7 (b). In this way, a seismic isolation ratio of 3.05/0.0.563 = 5.42. Similar considerations refer to Fig. 8, which looks at the second vibration mode.