Comparison on Wind-Resistant Design of Transmission Towers by Allowable Stress Method and Limit State Method

There are still many in-service 77/78 series transmission towers designed by the allowable stress method in the strong wind area. The power grid operation departments need to gradually carry out reinforcement and retrofit according to the applicable standards. According to the allowable stress method and the limit state method, the safety factor expressions of transmission tower members were given separately, and the wind load and structural design methods in the standards of different periods in China were compared and analyzed. Two 77/78 series transmission towers destroyed in 2021 wind disaster were selected as the research objects. The stress, stress ratios and safety factors of the transmission tower members were calculated according to the allowable stress method and the limit state method, respectively. The weak positions of the typical transmission towers under strong wind were determined. The safety factors of the transmission tower designed according to SDJ 3-1979 were significantly lower than that of SDGJ 94-90 and DL/T 5154-2002, and the difference in safety factors was more than 20%. The safety level of the transmission tower designed according to SDGJ 94-90 and DL/T 5154-2002 was basically the same.