## 3 Results
### Energy Dissipation  
The energy dissipation capacity of joints can be measured by an equivalent viscous damping coefficient \(h_{e}\). The larger the equivalent viscous damping coefficient \(h_{e}\) is, the better the energy capacity of the joint is. \(h_{e}\) can be calculated according to the following formula [25]:  
\[h_{e}=\frac{1}{2\pi}\times\frac{S_{AFBE}}{S_{ACEO}+S_{ADFO}} \tag{4}\]  
where \(S_{AFBE}\) is the area of the hysteresis loop, \(S_{ACEO}+S_{ADFO}\) is the sum area of \(\Delta CEO\) and \(\Delta DFO\), shown in Figure 24. The curve of \(AFBE\) is one cycle hysteresis curve. The area of the curve of \(AFBE\) represents the energy consumption of joints. \(C\) and \(D\) are the projection points of \(E\) and point \(F\) on the coordinate axis. Figure 23: Stiffness degradation curve. The relationships between the equivalent viscous damping coefficient and rotational angle on both sides of the positive and negative rotations are shown in Figure 25. It can be seen that the equivalent viscous damping coefficients of LJ-1 and LJ-2 decrease with the increase in rotational angle. The energy dissipation coefficients for LJ-1 and LJ-2 are roughly 0.1, while they are approximately 0.41 for LJ-3 and LJ-4. For LJ-1 and LJ-2 with variable cross-section damage under negative loading, the work carried out by the tearing of wood grain increases and the energy dissipation coefficients increase at the failure stage. The variable section damage has a great effect on the mechanical performance of the specimen. Energy dissipation capacity increases. The comparable viscous damping coefficients of LJ-1 and LJ-2 can be observed to be identical. During the slipping stage, the energy dissipation capacity of the joint is high. That is because the mortise and tenon experience friction at the initial loading and the energy dissipation capacity is significant. After slipping, the energy dissipation capacity of the joint decreases due to compression deformation of the tenon, which consumes little energy. External force is stored by the elastic strain energy produced by tenon bending, while the energy dissipated by plastic deformation generated by the extrusion between the tenon and the mortise is reduced. Therefore, the energy dissipation coefficient decreases. LJ-3 and LJ-4 have a long slipping stage. Equivalent viscous damping coefficients of LJ-3 and LJ-4 are similar. The friction between the mortise and the tenon is the primary source of energy consumption in two joints. Due to the mutual compression deformation using little energy and resulting in a loss in energy dissipation capacity, the equivalent viscous damping coefficient of LJ-3 diminishes. External force is stored by the elastic strain energy produced by tenon bending, while the energy dissipated by plastic deformation generated by the extrusion between the tenon and the mortise is reduced. Figure 24: Energy dissipation loop. Figure 25: Equivalent viscous damping coefficient. The energy dissipation coefficients for LJ-1 and LJ-2 are approximately 75% lower than that of LJ-3 and LJ-4. Therefore, it can be concluded that the energy dissipation capacity of loose joints is significantly higher than that of regular joints. This because the slipping stage of a loose joint is longer than that of a regular joint, which can assume more energy with higher energy dissipation. According to the curve of the equivalent viscosity and damping coefficient with the change in the rotation angle, the equivalent viscous damping coefficient is high in the slipping stage. The mortise and tenon then compress with each other, and plastic compression deformation occurs with the increase in rotational angle. When the plastic deformation increases to a certain extent, energy-consuming capacity will not increase. Energy consumption capacity of the joint gradually decreases. Finally, wood fibre torn at the variable cross-section at the failure stage consumes more energy and energy dissipation capacity increases.