# Mechanical Performance of Confined Autoclaved Fly-Ash-Brick Masonry Walls under Cyclic Loading
## 3 Numerical Simulation Analysis and Verification
### Vertical Compressive Stress on Seismic Performance of the Walls  
It is well known that there are three failure modes of the masonry wall including shear-friction failure, shear-compression failure and diagonal-compression failure with the increase of vertical compressive stress [36]. Vertical compressive stress has a significant impact on the shear strength of a masonry wall no matter what kind of failure occurs in the wall. From a nine-story residential building, [PERSON] [37] concluded that the smallest vertical compressive stress located at the top floor was 0.2 MPa, the vertical compressive stress of the middle layer was assigned to 0.6 MPa, and the largest vertical compressive stress at the bottom floor was 0.9 MPa. According to the result, the vertical compressive stresses at the top of wall were 0 MPa, 0.2 MPa, 0.6 MPa and 1.0 MPa to simulate the different layers in the building. The dimensions and parameters of walls ZWZ-1, ZWZ-10 ZWZ-11 and ZWZ1-12 are shown in Table 6. From Equation (9) and simulation results, the bearing capacity values of the walls with vertical compressive stress are shown in Table 10. The load-displacement and stiffness-displacement curves of the walls with different vertical compressive stress are shown in Figure 28. The plastic strain magnitudes of the walls with different vertical compressive stress are shown in Figure 29.  
Figure 28: Load–displacement and stiffness–displacement curves of the walls with different vertical compressive stress: (**a**) load–displacement curves; (**b**) stiffness–displacement curves.  
Figure 29: Plastic strain magnitude of the walls with different vertical compressive stress: (**a**) wall ZWZ-10; (**b**) wall ZWZ-11; (**c**) wall ZWZ-12.  
From Table 10, compared to wall ZWZ-10 without the vertical compressive stress, the cracking loads of walls ZWZ-11, ZWZ-1 and ZWZ-12 were increased by 34%, 99% and 92% respectively, and the ultimate loads of walls ZWZ-1, ZWZ-11 and ZWZ-12 were increased by 5%, 52% and 43% respectively. With the vertical compressive stress increased, the cracking and ultimate loads of those walls increased at first and then decreased, but the ultimate displacement of those walls decreased. According to Figure 28, with the increase of the vertical compressive stress, the initial stiffness values and stiffness degradation rate of the walls increased, but the bearing capacity values of those walls increased at first and then decreased. The reason is that the shear-friction failure occurs in the wall when the vertical compressive stress is small, and then the friction increases with the increase of the vertical compressive stress to weaken the horizontal sliding of the wall. However, when the vertical compressive stress exceeds 0.6 MPa, diagonal-compression failure occurs in the wall and the bearing capacity and displacement of the walls decreased.  
From Figure 29, the PEMAG value changed along the diagonal of the wall, and its distribution was the same as the X-type fracture distribution caused by shear failure of the wall. The color of each unit in the graph was deepened, indicating that the deformation of each unit increased. The PEMAG value of each unit of the wall was cumulative for analyzing the wall deformation with different vertical compressive stresses. With the increase of vertical compressive stresses, the wall deformation increased.