## 3 Pseudo-Dynamic Tests and Numerical Analysis of Model Structure  
### Introduction of Test Program  
Due to limitation of the test field, a scaled sub-structure was selected from the prototype structure, as shown in Figure 3. The scaling factor for length L was determined as 1/8. Other scaling factors can be obtained by the principle of dimensional analysis [24]. Figure 3 shows the layouts and dimensions of test specimen. Figure 4 shows the steel arrangements of the RC tubular column. Considering there were no proper shaped steel to simulate the scaled steel truss, square hollow steel tubes were selected to fabricate the steel truss used in the specimen. The cross section details of the steel truss are shown in Figure 5. Table 2 provides the material properties of steel used in the specimen. The actual compressive and tensile strength of concrete used for the tubular columns were 28.3 and 2.5 MPa, respectively. The modulus of elasticity of concrete was 3.22 \(\times\) 10\({}^{4}\) N/mm\({}^{2}\).  
Figure 3: Layouts and dimensions of test specimen (unit: mm): (**a**) Sub-structure selected from the prototype structure; (**b**) Plan layout of reinforced concrete (RC) tubular columns; (**c**) Elevation view along the direction of A-shaped frames.  
Figure 6 shows the test setup. Two hydraulic actuators were fixed respectively at the middle part of steel truss platform (6.563 m) and the top of A-shaped frame (8.106 m). The lower actuator located on the middle part of steel truss was set as the main control point. The loading protocol of each actuator was controlled by an online computing system capable of operating the PDT procedures. The input forces provided by the actuators was calculated by the Newmark-\(\beta\) method during the online PDT procedure [16].  
Figure 4: Steel arrangements of the RC tubular column (in mm).  
Figure 5: Cross sections of members in steel truss (unit: mm): (**a**) Elevation view of plane trusses in ���⃝, A, E axises; (**b**) Elevation view of plane trusses in �⃝, ⃝, B, D axises; (**c**) Elevation view of plane trusses in ⃝, C axises (The axises were designated in Figure 3).  
The initial 8 s of El-Centro (NS) record was selected as the input ground motion for its ample spectral components and adaptability to the sites. Based on the time scaling factor of \(1/\sqrt{8}\), the duration and time interval of the input ground motion were determined as 2.8 s and 0.0035 s, respectively. Seven intensity levels of PGAs with 0.05, 0.10, 0.20, 0.30, 0.40, 0.60 and 0.80 g were used to simulate different hazard levels of earthquakes. In addition, free vibration with duration of 1.75 s was added for each loading case to investigate the changing rules of dynamic characteristics with the increase of PGA. Therefore, each PGA level was finally loaded by 800 steps (2.8 s) and subsequent 500 steps (1.75 s).  
The loading ratio between the two actuators was 1:1.28, which was derived by the first mode vibration and mass matrix [16]. During the whole loading process, lateral displacements were recorded by the displacement meters (e.g., D-1) laterally installed on the top of A-shaped frame, middle part of steel truss, corbel, middle part of column and ground beam, as shown in Figure 6.