The results of the Section 4-4 showed that the Metro Station remain within the elastic range for a seismic input characterized by a return period equal to 1000 years. On the contrary, for the seismic input characterized by a return period equal to 2450 years, only the section near the intermediate slab shows localized plastic deformation. For the Section 2-2 the same considerations could be made.
CONCLUSION
Seismic response of Mercato Santa Anita Metro Station to two seismic inputs characterized, respectively, by a return period equal to 1000 years and 2450 years shows:
- an elastic behavior of the retaining walls for a seismic input characterized by a return period equal to 1000 years;
- for the seismic input characterized by a higher return period, the Station shows localized plastic deformations only in the section near the intermediate slab. This behavior is considered acceptable for the Maximum Design Earthquake because the public life safety is guaranteed.
Taking as a reference the static case, the maximum increment of bending moment during the earthquake is equal to 700 kNm for the operating design earthquake and 1100 kNm for the maximum design earthquake. The results of the analysis indicate a complex response of the system due to particular soil-structure interaction effect and local seismic response phenomena because the soil response is related to the vibration modes excited by the signal. It may be noted that the signals, now taken into account, gives rise to possible soil resonance with the first vibration mode, which leads to increasing shear strain in the deeper soil layers, and, consequently, additional damping according to the strongly nonlinear soil behaviour (Figure 25).