**3. Seismic-Performance-Improvement Schemes**

## *3.1. The FPBs Scheme*

The analysis in Section 2.4 indicated that the shear resistance of the spherical steel bearings on the arch crown and the tops of columns 1 # and 10 # was insufficient; that is, the anti-seismic calculation of the bearings failed, and transverse anti-seismic measures needed to be taken. The seismic isolation's design using FPBs is mainly discussed in this paper.

The FPBs adopt lag-system simulation, and the simplified calculation model for FPBs is shown in Figure 7. The main design parameters of each FPB obtained through repeated optimization calculations and verifications are presented in Table 3.

To verify the reliability of the FPB parameters, a testing company was entrusted to conduct a pseudo-static test on the FPB-7000, and the measured hysteresis curve of the FPB-7000 was obtained. The test results were compared with the finite element simulation results, as shown in Figure 8; the hysteresis curve of the FPBs in the finite element analysis was very close to the experimental results, which verified that the parameters of the FPBs in this paper were set accurately and that the mechanical properties of the FPBs were simulated accurately.

**Figure 7.** Simplified calculation model for FPB.

**Table 3.** Design parameters of FPBs.


**Figure 8.** Hysteretic curve of FPBs.

To study the effect of the FPBs on the seismic performance of the long-span deck CFST arch bridge and the influence of its layout on the seismic performance of the bridge, a variety of layout schemes were developed, and the isolation effects were compared to obtain the optimal scheme. Due to space constraints, the results are presented here directly. Considering the excessive displacements of the FPBs under E2 excitation in the full bridgeisolation scheme, the optimal plan involves replacing only the spherical steel bearings with shear failure in the original plan; that is, the spherical steel bearings at the top of the vault and on the side column are replaced by FPBs. The bearing-layout scheme is summarized in Table 4, where TJQZ is a spherical steel bearing. The spherical steel bearings passing the shear-resistance-checking calculation in Table 1 are retained in this scheme. This scheme is called Model 1. It should be noted that because the main beams at the junction of the main approach bridge are not connected, the main beams at the junction of the main approach bridge suffer a high level of relative displacement under earthquake excitation. To prevent the relative displacement between the main beams from leading to dislocation between the tracks, which would affect traffic safety, the structural measures that limit the relative displacement in the transverse direction were adopted between the main beams of the main approach bridge, and the elastic connection was used in the finite element model to simulate the displacement-limiting effect of the structural measures.


**Table 4.** Layout scheme of the bearings in Model 1.
