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:
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).