## 3 Results and Discussion
### Scale Model Test  
To investigate the mystery of the Forbidden City's favorable seismic performance, a scale model of Shoukang Palace, which was commonly the bedchamber of the emperor dowager, was made at a 1:5 ratio to conduct a series of earthquake simulation tests by [PERSON] et al. [16; 17; 18; 19], as shown in Figure 11 and Table 1. The El-Centro wave was selected in consideration of the site type (Class II) of the Forbidden City, which acts on the model in both x and y directions. The ratio of peak accelerations in x and y directions is 0.85 [16]. The shaking table reproduces the energy of quakes in an increasing order of magnitude, and the earthquake duration at each tremor lasted 30 s. The initial test earthquake magnitude is 4.0, and the magnitude rose in increments of 0.5, a magnitude of 5.0 has thirty-two times the energy of a magnitude of 4.0. At a 4.5 magnitude, the model showed mild shaking. At a 5.0 magnitude, the model started shaking, the columns slightly tilted, the Dougong bracket was strained and one side the masonry collapsed. At a 7.5 magnitude, the shaking of the model intensified, the columns were significantly tilted, and the remaining side of the masonry collapsed, but the traditional wood frame was still standing strong. At a 9.0 magnitude, the stone bases shifted around, the model shook violently, the columns tilted more significantly, and a tugging noise between wood elements was heard. At a 9.5 magnitude, which is the largest magnitude that has ever been recorded for the Beijing area and is equivalent to 2 billion tons of TNT, the model shook more violently, the columns tended to collapse, and the tugging noise increased. Ultimately, at a 10.1 magnitude, the model shook drastically, and the tendency of the columns to collapse increased, but the wooden structure still stood firmly. At the end of the test, it was found that both sides of the masonry had collapsed, while the superstructure showed no noticeable damage, and nor did the column. Figure 11: A 1:5 scale model of Shoukang Palace earthquake test map. The experimental results show that the physical properties of wood, the application of tenon-mortise joints and the shallow-buried columns are the main factors of excellent seismic performance of ancient Chinese wooden buildings. Wood is a kind of building material with light weight and good mechanical properties. It is easy to deform when the external force acts, while it also has enough displacement restoring capacity, which reduces the structural damage caused by an earthquake. Tenon-mortise joints are commonly used in ancient buildings, which make the whole wooden building more flexible, as shown in Figures 12 and 13 [16]. Tenon-mortise joints have a semi-rigid connection [20]. These semi-rigid joints (tenon-mortise joints) have high ductility, which enables the redistribution of internal forces within the structure. High ductility in joints is very important for dynamically, cyclically loaded structures (dissipation of energy). Although the tenon-mortise joint weakens the effective bearing area of the wood structural component, which leads to reduced bearing capacity at the joint site, the remainder of the load-bearing capacity of the wood structure is still strong [21]. Thus, the weakened wooden sections can still withstand heavy loads. Moreover, the tenon-mortise joints bind wooden components firmly while leaving space for them to loosen, and allow them to work both as individual units and together. During earthquakes, the components rub against each other and rotate, which easily creates severe deformations, offsets the strong impacts of the earthquakes and reduces the seismic response of the structure and the load of the key part [22; 23; 24]. Thus, the structure is extremely strong and flexible, making full use of the flexibility of these semi-rigid joints.