Study on the Influence of Chloride Ion Corrosion on Wind-Induced Vibration Response of Transmission Towers in Coastal Area

Transmission tower structures in coastal areas suffer from the long-term erosion of the corrosive atmosphere, and the effective bearing area of its components is reduced due to corrosion, and the mechanical properties are gradually reduced. The service safety and durability of transmission tower structure are seriously threatened under the coupling action of long-term environmental corrosion and coastal wind. In order to accurately characterize the mechanism of long-term chloride ion erosion on the wind-induced dynamic response of the coastal transmission tower structure system, this study first uses the laboratory to conduct accelerated salt spray corrosion tests on the transmission tower angles, the corrosion duration is set to 0 h, 800 h, 1 600 h and 2 400 h respectively. Then, tensile specimens were made of corroded angle steel and mechanical properties were tested by MTS testing machine to explore the influence of corrosion on the cross section loss rate and mechanical properties degradation of angle steel, and to build a regression model of corrosion duration(cross section loss rate) and mechanical properties parameters of angle steel. Finally, the constitutive model of corroded angle steel was described based on the modified secondary flow tracing model, and the finite element analysis software Sap2000 was used to establish the finite element analysis model of transmission tower structure considering the influence of corrosion. Wind-induced vibration response of transmission tower line structure system was analyzed to explore the influence mechanism of coastal chloride ion erosion. The results show that: with the increase of chloride ion erosion time, the mechanical properties of angle steel showed a gradual decline trend. When the corrosion time was 800 h, the ultimate strength and yield strength degradation rate were 4.00% and 3.01%, respectively, the elongation and elastic modulus of angle steel decrease by 5.33% and 7.02%, respectively. When the corrosion time reached 2 400 h, the degradation rates of both reached 16.49% and 15.22%, respectively, compared with the non-corrosion condition. After 2 400 h of corrosion, the decreasing amplitudes reach 9.74% and 14.33%, respectively. Through the dynamic analysis of transmission tower structure, it is found that with the accumulation of corrosion, the natural vibration frequency of transmission tower structure decreases gradually. When the corrosion is as long as 2 400 h, the first-order natural vibration frequency of the transmission tower structure decreases by 4.08% compared to non-corrosion condition, and the corrosion has a more significant effect on the high-order frequency of transmission tower structure. Corresponding to the three corrosion conditions(corrosion time is 800 h, 1 600 h and 2 400 h), the wind vibration displacement response of the transmission tower structure and the stress of the tower rod show a gradual increasing trend. When the corrosion time reaches 2 400 hours, the maximum displacement of the tower top reaches 0.466 m, which increases by 9.8% compared with the non-corrosion condition. The maximum increase of rod stress is 5.1%. The yield strength ratios of the maximum stress under the same wind load and the corresponding corrosion time under the four conditions are 0.52, 0.55, 0.58 and 0.60, respectively.