## 3 Devices Setup and Field Test
### Establishment of Structure Numerical Model  
Previous studies have reported that the finite element analysis (FEA) using PERFORM-3D showed good calculation accuracy and efficiency [25], can better capture the yield situation, truly reflect the basic characteristics and nonlinear behavior of the structure, and has certain reliability [26]. Therefore, PERFORM-3D is used to simulate and analyze the structure due to the structure's inelastic features.  
The fiber model (\"column, inelastic fiber section\") and the plastic hinge model (\"moment hinge, curvature type\") are used as material models to represent the column's and beam's plastic zones, respectively. When a part achieves its maximum bearing capacity, the plastic hinge uses the moment curvature model to determine the yield stress, moment, and curvature. The column is constructed using three-dimensional fiber elements consisting of eight steel fiber elements and thirty-six concrete fiber elements, which is sufficient to yield a consistent stress-strain analysis finding. The following is a description of the modeling process:  
(1) Simulation of a unit. Considering the calculation efficiency and analysis accuracy, the frame columns and beams are simulated by the fiber model and the concentrated plastic hinge model respectively. The plastic hinge utilizes the moment curvature model to determine the member yield and the corresponding moment and curvature when the beam section reaches its bearing capacity.  
(2) Simulation of the constitutive connection of steel. The steel is Q235. The constitutive connection is based on the two broken line model considering follow-up hardening [27], and the stiffness ratio of steel after yield is taken as 0.01. The model can well describe the stress-strain relationship of steel and accurately simulate the mechanical properties of steel.  
(3) Simulation of a concrete constitutive relationship. The concrete model is based on the Kent-Park model, which takes into account the deterioration of concrete's hysteretic energy without taking into account the material's tensile strength. The reason for omitting the tensile strength is that the additional mass of the floor slab is primarily simulated, and so has no effect on the simulation result. The compressive strength of the concrete is 20.1 MPa. The strength grade of the concrete is C30. After calibrating the material model parameters, they are entered into the finite element model.  
By establishing two numerical models of isolated and seismic structures, we found that the bottom shear damping rate (i.e., the damping coefficient of Chinese code [15]) of isolated structure under moderate earthquake is 62%; Under severe earthquake, the damping rate of the floor acceleration is >60%, and that of the interlayer displacement is >65%. Except some columns at the bottom layer that are in elastic-plastic state, the rest of the superstructure are in elastic state, which fully shows that the isolated structure has good shock absorption capacity. The detailed comparison of the seismic responses of the two models is not discussed in detail bacause this study focuses on the structural dynamic characteristics of isolated structures during field tests.  
Figure 17 illustrates the three-dimensional finite element model. The simulation results of seismic structure model are compared with the test results of horizontal initial displacement release, and the analysis results are discussed in Section 4.  
Figure 17: Finite element model of seismic structure.