## 4 Results and Discussion
### Stress Behavior of Shear Keys  
It can be seen from Section 4.3.2 that the peak shearing force in the transverse and vertical directions of the segment joint appears in shear key E and shear key B, respectively. The stress vector diagrams of shear key B and shear key E were extracted for further analysis, as shown in Figures 22 and 23. In order to clearly see the stress vector diagram inside the shear key, the shear key is cut into three entities along the axial grid line. The three entities of horizontal shear key E are marked as H1, H2, and H3, and the three entities of vertical shear key B are marked as V1, V2, and V3. As shown in Figure 20, the plane 3-4-4\({}^{\prime}\)-3\({}^{\prime}\) is the root of the shear key, i.e., the position of the shear key connecting to the immersed segment. The corresponding plane 1-2-2\({}^{\prime}\)-1\({}^{\prime}\) is the end of the shear key. H1 and V1 are the entities which connected to the main body of the immersed segment. The maximum principal stress in Figures 22 and 23 represents the tensile stress, while the minimum principal stress is the compressive stress. The relative direction of the arrow represents the compressive stress vector, the opposite direction of the arrow represents the tensile stress vector, and the length of the arrow represents the stress value. According to Figures 22 and 23, the maximum stress of the shear key under an earthquake is compressive stress, while the tensile stress is relatively small. The tensile stress is mainly concentrated at the root of shear key and decreases from the root to the end. Meanwhile, the compressive stress distribution of the shear key is relatively uniform. The end and root of the shear key are subjected to large compressive stress, and the maximum compressive stress appears at the end of shear key. Moreover, the tensile stress of the shear key has a certain angle with the horizontal plane, while the tensile strength of the concrete is low, and the root of the shear key is prone to produce a certain angle of tensile crack, which is consistent with the experimental phenomenon observed by [PERSON] and [PERSON] [44]. Under the action of an earthquake, the shear key tenon and shear key groove squeeze each other, and the compressive stress at the end angle of the shear key is large, where stress concentration and damage can easily occur. In order to clarify the change in the stress level of shear key with the incident angle, the tensile stress time history of the root node of shear key B and the compressive stress time history of the end node of shear key E were extracted for analysis, as shown in Figures 24 and 25. We can see from the figures that the stress of the shear key experiences severe fluctuations in the period of 7-15 s, and the maximum value appears near 8.52 s, but different incident angles have different time delays. This performance is similar to the fluctuation characteristics of the input seismic wave, indicating that the stress fluctuation on the shear key is mainly affected by the input seismic wave. The initial value of the shear key stress time history is not 0, indicating that the shear key is subjected to a certain static force before the dynamic calculation, which is mainly caused by self-weight and  
Figure 21: Shearing force of segment at different angles of incidence: (**a**) transverse; (**b**) vertical. hydrostatic pressure. As the incident angle increases, the stress of vertical shear key B increases, and the stress of horizontal shear key E decreases. The oblique incidence makes the stress distribution of shear key more complicated. This was also mentioned in the previous section, which is related to the change in the horizontal and vertical components caused by the oblique incidence. The tensile strength of concrete material is low; hence, the tensile stress is an important index to evaluate the safety of shear key. The maximum tensile stress of shear key E reaches 3.65 MPa, which exceeds its ultimate tensile strength, indicating that shear key E is damaged.