# Seismic Effect of Marine Corrosion and CFRP Reinforcement on Wind Turbine Tower
## 3 Numerical Analysis of Seismic Dynamic Response
### Bending Moment-Curvature and Plasticity Rate Analysis of Wind Turbine Tower  
Figure 16 shows the equivalent plastic strain values of the materials in the corrosion area of the wind power tower in 0, 10, 20 and 30 years when PGA = 2G under the Nihonkaia-Chubu earthquake loading. It can be seen from Figure 16 that the maximum plastic strain value of the noncorrosive structure is 0.0038. With the increase of corrosion time, the plastic strain value of the material gradually increases, and the maximum plastic strain value of the structure corroded for 30 years reaches 0.015, which is 2.95 times larger than that of the noncorrosive structure. Moreover, it can be seen from the area surrounded by the plastic  
Figure 14: The Nihonkai-Chubu earthquake: (**a**) structural APRC value; (**b**) maximum Mises stress.  
Figure 15: The Hyogoken-Nanbu earthquake: (**a**) structural APRC value; (**b**) maximum Mises stress.  
strain curve that the corrosion leads to the acceleration of the plastic development of the tower in the corrosion area.  
The yield curvature, maximum removal rate and structural plasticity rate of the tower structure under different corrosion years are calculated according to the guidelines for design of wind turbine support structures and foundations [35], as shown in Figure 17. It shows that the yield curvature of the tower structure does not change with the increase in corrosion years, but the maximum curvature decreases from 0.00217 m\({}^{-1}\) to 0.00184 m\({}^{-1}\). The corresponding structural plasticity rate is reduced from 2.306 to 1.954, and the seismic performance of the structure is obviously reduced.  
In order to explore the influence of corrosion degree on the nonlinear development of wind turbine tower structures, the Nihonkai-Chubu earthquake of PGA = 2.0 g is selected. The moment curvature hysteretic curves of the wind turbine tower structure under four different corrosion conditions are calculated, respectively. The moment curvature hysteretic curve of the corrosion area is extracted, as shown in Figure 18. It shows that the maximum curvature of the noncorrosive structure under the Nihonkai-Chubu earthquake is 0.0013 m\({}^{-1}\), and the maximum plasticity rate is 1.38, which is less than the allowable plasticity rate of 2.306. The maximum curvature value of the structure corroded for 10 years is 0.003 m\({}^{-1}\), the maximum plastic rate is 3.14, which is larger than 2.263 higher than the maximum allowable plastic rate of the structure. The maximum curvature of the structure corroded for 20 years and 30 years is 0.0059 m\({}^{-1}\) and 0.0058 m\({}^{-1}\), respectively, and the  
Figure 16: Equivalent plastic strain of corrosion area structure: (**a**) Section position; (**b**) Equivalent plastic strain of section B-B.  
Figure 17: Bending moment curvature relationship of different corrosion structures.  
maximum plasticity rate is 6.27 and 6.16, respectively, which is beyond the maximum allowable plasticity rate of the structure. It can be seen from the fullness of the hysteresis loop that with the increase of corrosion time, the larger the area surrounded by the hysteresis loop, that is, when the structure is corroded, greater plastic deformation is needed to dissipate seismic energy under the same seismic action.