## 5 Verification of Real-time Hybrid Control System
### Three-DOF Structural Dynamic Test with Steel Structure
#### 5.1.3 Non-Linear Dynamic Test with Real-Time Hybrid Control System  
In this section, a nonlinear test was performed to prove the reliability of the hybrid control system. The magnitude of the incremental coefficient for the nonlinear dynamic test was determined to be larger than the displacement (40.07 mm) to be obtained in the non-linear range by applying yield stress to the cantilever beam of 2.4 m. As a result, the incremental coefficient for seismic load was set to 2 for linear dynamic test and 6 for nonlinear section analysis. Figure 11 showed the results of the first and second layers by the numerical analysis with the hybrid numerical analysis, respectively. The maximum displacement was about 7% and 1% in the 1 st and 2 nd floors, respectively, and it could be said that the numerical analysis and the experimental data can be in good agreement. In addition, the permanent deformation occurred in the structure after the maximum displacement, it could be seen that the graph was much lowered from the origin after 100 s. After then, a slight difference between displacement and numerical value was observed. This error can be attributed to the damping ratio used in the numerical analysis. The damping ratio of the test specimen is calculated by performing the free vibration test of the test specimen, which includes various errors in the test process and has a limitation on its reliability. In addition, the value used as the material model may include some errors in the nonlinear analysis, and finally, the experimental error between the actuator and the experiment to  
Figure 10: Force vs. displacement at 1 st floor.  
Figure 9: Comparison of numerical and hybrid test result.  
realize the multiple degree of freedom may be considered. Therefore, if an error reduction is developed more, it may be considered a more reliable experiment.  
Figure 12 shows the results of the horizontal displacement and shear force on the first floor, and Figure 13 shows the values measured by the accelerometer on the first floor. As shown in Figure 12, when the maximum displacement of about 60 mm occurs, the load is 40 kN, resulting in residual strain. This shows that the acceleration occurred at 1.7 g as shown in Figure 13. In addition, Figure 14 shows the response history measured by the strain gauge installed at the lower part of the test specimen, and it can be seen that after the maximum displacement, residual deformation occurs in elasticity in both the flange and the web and transfer to plasticity. The permanent strain measured at the flange is about 200-250 \(\upmu\)m and about 490 \(\upmu\)m on the web. Therefore, it can be inferred that the residual strain generated in the first and second layers is due to the deformation of the end of the test specimen.  
As a result of this experiment, in order to predict nonlinear behavior of steel frame structure, it can be grasped through numerical analysis and shaking table test. However, because numerical analysis depends on numerical approximation of the behavior and material properties of the structure, it is difficult to accurately predict the behavior of a complex concrete structure. Therefore, applying real-time hybrid experiments