## 4 Model Establishment
### Experimental Validation of the Model  
To verify the accuracy and rationality of the parameters of structural analysis software and computational structural models, this paper simulated the low-cycle cyclic loading model of a drop-frame structure completed in the structural laboratory of Chongqing University [5]. The test site loading device is shown in Figure 6, and the dimensions and reinforcement details of the experimental drop-frame structure are shown in Figure 7.  
(1) Experimental Model and Loading System  
The prototype of the experiment had a total of 8 stories, with a drop of 2 stories over 1 span, and a total of 3 spans. The design seismic intensity was 8 (0.2 g), the seismic design group was Group 1, the site category was Category II, the concrete strength grade was C30, longitudinal reinforcement adopted HRB400, and stirrups adopted HPB300. The experimental model had a total of 5 stories, with a drop of 2 stories over 1 span, and its geometric dimensions were one-quarter of the prototype frame. Each story had a height of 750 mm, and each span was 1500 mm. Section dimensions were as follows: beams were 100 mm \(\times\) 150 mm, and columns were 150 mm \(\times\) 150 mm. The horizontal and vertical loads on the model were applied using hydraulic jacks. For the beams, loads were applied using steel plates. Vertical loads were transferred to  
Figure 6: The test site loading device. Figure 7: Structure dimensions and reinforcements of the step-terrace structure in the test. the column tops through steel beams in proportions of 10 kN for end columns and 5 kN for intermediate columns. Horizontal loads were applied as reciprocating loads under displacement control at a ratio of 1:2 only at the third and top stories. (2) Numerical Simulation  
The comparison between experimental results and software-simulated overall hysteresis curves is shown in Figure 8. It can be observed from the figure that the maximum horizontal thrust for both cases was around 100 kN, and the general trends of the hysteresis curves were relatively consistent. The overall error was within an acceptable range, indicating that the degradation behavior of the bearing capacity and stiffness of the mountain landslide frame structure under reciprocating loads can be simulated relatively accurately. Additionally, the differences in pinching phenomena between the two hysteresis curves were small, indicating that the OPENSEES 3.3.0 structural analysis software can effectively simulate and analyze the mountain landslide frame structure model. The circle in Figure 9 represents the appearance of plastic hinges in the section, and the color represents the degree of plastic hinge development, from green to blue, yellow, pink, and red, representing the increasing degree of plastic hinge development. By comparing the hinge distribution results with the experimental crack patterns, it can be observed that the numerical simulation results were quite close to the experimental results. The only significant difference was in the hinge results of the top floor. According to the literature, the top floor crack patterns were not drawn in the experiment due to safety considerations and lateral support obstructions. However, based on the longitudinal reinforcement strain gauge values, plastic hinges did form in the top floor columns and side span beams, which is consistent with the OPENSEES analysis results. Figure 8: Hysteresis curves of horizontal force. Figure 9: Comparison of hinge distribution diagrams: (**a**) experimental results and (**b**) OPENSEES results. Overall, however, the failure modes of both were relatively similar: the upper-ground floor columns had more hinges compared to the lower-ground columns. Additionally, the upper-ground floor columns exhibited hinges at both the top and bottom ends, reaching their ultimate state, indicating that the upper-ground floor was a distinctly weak layer. In contrast, the lower-ground columns only had significant hinge formation at the bottom end, which is consistent with the experimental results.