# Seismic Response and Mitigation Analysis of a Subway Station in the Site with Weak Interlayers
## 3 Seismic Mitigation Effect of FPB in Weak Interlayer Site
### The Seismic Mitigation Effect of FPB
Figure 28: Difference in the maximum displacement of the side wall and column with different shear wave velocities. (**a**) Side wall. (**b**) Upper column. (**c**) Lower column. Figure 29: _Cont._  
Figure 30 compares tensile damage nephgrams of the structure under two unfavorable conditions and in a layered soil site. From this illustration, it is evident that the central column of the original structure is nearly destroyed, while the seismic mitigation structure experiences only minor tensile damage. When the subway station structure is situated in a site with a weak interlayer, the implementation of FPB shifts the damage that occurs at the connection of the top and bottom slabs with the central column to the connection points between the top and bottom slabs with the side wall. During an earthquake, the damage to the central column typically occurs earlier than that to the side wall. The use of FPB can effectively mitigate the seismic damage to the central column, ensuring the protection of the subway station structure. To provide a more intuitive illustration of the seismic damping effect of FPB in a site with a weak interlayer, the shear forces and bending moments on the bottom of the structural central column between the original and seismic mitigation structures are compared. In this context, the damping ratio is employed as the criterion for evaluating the damping effectiveness. The damping ratio can be defined using Equation (7) in this context. \[\gamma=\frac{A_{0}-A_{R}}{A_{0}} \tag{7}\]  
In the equation, under the same conditions, \(A_{0}\) represents the internal force values within the top and bottom cross-sections of the central columns of the original structure, while \(A_{R}\) represents the internal force values within the top and bottom cross-sections of the central columns of the seismic mitigation structure. Figure 31 provides the damping ratio plots for structures under different site conditions. It can be seen from Figure 31 that the damping ratio of the seismic mitigation structure in the weak interlayer site is higher compared to that in the layered soil site. This implies that the seismic mitigation effect of FPB in weak interlayer sites surpasses their seismic mitigation effect in layered soil sites. The maximum damping ratio observed in the shear force of the central column could reach 94%. The central column of the subway station structure is the component most vulnerable to seismic forces and prone to shear failure under seismic motion. The seismic mitigation scheme with FPB on the top of the central column of the subway station in a site with a weak interlayer can effectively reduce the damage to the subway station structure, demonstrating excellent seismic mitigation effects. Therefore, when the station is situated on a site with a weak interlayer, the use of FPB for seismic design is worth considering. Figure 29: Interstorey displacement angle of the station under different conditions. **(a)** Thickness of the interlayer. **(b)** Positions. **(c)** Shear wave velocity. Figure 25.0 _Cont._  
Figure 25.1 Tensile damage of the station under different conditions. (**a**) H= 3 m at 0.4 g (original structure). (**b**) H = 3 m at 0.4 g (shock absorption structure). (**c**) Middle at 0.4 g (original structure). (**d**) Middle at 0.4 g (shock absorption structure). (**e**) Layered soil site at 0.4 g (original structure). (**f**) layered soil site at 0.4 g (shock absorption structure).