**5. Experimental Validation**

*5.1. Overview of the Test*

5.1.1. Experimental Setup

To validate the effectiveness of the proposed *H*∞ control method, actual real-time hybrid simulations were conducted on an SDOF structure. The loading system at the Structural and Seismic Testing Center of Harbin Institute of Technology was employed, which consists of an FTS system and a dSPACE 1104 board. The FTS system comprises a servo-hydraulic actuator, displacement sensor, force sensor, and servovalve. The displacement sensor is an LWH-200 with a maximum stroke of 200 mm, which is produced by Novotechnik. The force sensor is PSD-5tSJTT with a capacity of 5 T, which is produced by Vishay. The servovalve is MOOG-761-3005, produced by Moog. The experimental setup is shown in Figure 18.

**Figure 18.** Loading system setup. (**a**) FTS system; (**b**) control hardware and system.

Considering the restraints of the loading system, a spring was taken as the specimen and was loaded in the axial direction. In RTHS, the central difference method was adopted to solve the equation of motion, and the time integral was 0.02 s. The equation of motion solved by the LSIM command in MATLAB served as the exact reference solution, where the time step was 0.02 s.

To diminish the effect of measurement noise, an elliptic filter was designed by the digital filter design module, with stop frequencies of 100 and 30 Hz for displacement and force, respectively. The sampling time for the filter was 1000 Hz.
