| The transmission tower is a tall truss steel structure,which is formed by connecting equilateral angle steel or steel pipe by gusset plates and bolts.The southeast coastal area of China is affected by the East Asian monsoon(normal wind)and the Northwest Pacific typhoon all the year round.For the wind-sensitive structure,like the transmission tower,the research on its wind resistance has always been an important concern.In addition to being affected by strong winds throughout the southeast coastal areas,its marine and industrial atmospheric environments will corrode the steel transmission towers,causing their carrying capacity to decline.Based on the influence of the above load end and structure end on the service period of transmission towers,this paper analyzed the mixed wind environment in Ningbo area,predicted the atmospheric corrosion depth of carbon steel in Ningbo area,and evaluated the wind resistance performance of corroded transmission towers in Ningbo area by numerical simulation.It mainly includes the following four aspects:(1)Wind climate assessment of construction site considering the correlation of mixed climate wind directionTaking Ningbo as an example,a method for estimating wind speeds in multiple wind directions considering the correlation of mixed climates was proposed to more accurately estimate the structural design wind speeds of power transmission tower construction sites in the mixed climates of the region.First,the 600 years typhoon wind speed samples in Ningbo was obtained by the full-path simulation method,among which the Yan Meng model was selected as the wind field model;the typhoon samples were deleted and the normal wind speed samples were obtained based on the measured data of the Ningbo weather station.Then,the wind speed samples of typhoon and normal wind were classified into each wind direction,and the edge distribution model of mixed climate extreme wind speed was established.Finally,the joint distribution model of wind speed and direction was established in Ningbo area by the Copula function,which was used to obtain the multi-wind direction extreme wind speed estimation value considering the correlation of the mixed climate in Ningbo area.(2)Prediction of Carbon Steel Corrosion Depth in Atmospheric EnvironmentA long-term prediction model of carbon steel corrosion depth in different atmospheric environments was obtained based on the corrosion data of carbon steel exposure tests in different atmospheric environments around the world(marine atmosphere,industrial atmosphere,urban atmosphere,rural atmosphere,urban-marine atmosphere and industrial-marine atmosphere);the long-term corrosion depth prediction value of carbon steel in the atmospheric environment of Ningbo area was obtained based on the environmental climate of various areas in Ningbo and the long-term prediction model of carbon steel corrosion depth,which provided a reference for the development of transmission tower corrosion.(3)Analysis of Wind Vibration Response of Corroded Steel Transmission TowerThe ZM4 linear transmission tower finite element model was established by using ANSYS.The influence of atmospheric corrosion on the reduction of the section of the transmission tower angle steel was considered based on the prediction of the carbon steel corrosion depth in the atmospheric environment in Chapter 3;In addition,Choosing the extreme wind speed in 50 years under the mixed climate wind direction 2in Chapter 2(the wind direction where the maximum wind speed is located)as the design wind speed.The pulsating wind speed time history was generated by the harmonic superposition method and converted to obtain the wind load time history based on MATLAB,which was loaded into the finite element of the transmission tower for wind vibration response analysis.The influence of wind direction angle,design wind speed,atmospheric corrosion and service life on wind vibration response was discussed.(4)Analysis of Wind Disaster Vulnerability of Corroded Steel Transmission TowerThe transmission tower structure under ocean-industrial atmosphere(the most severely corroded)was selected as the research object based on the carbon steel atmospheric corrosion depth prediction model established in Chapter 3.First,a large amount of wind load time history was obtained by simulation,and the wind load action effect function was obtained by incremental dynamic time history analysis(IDA)was performed on the transmission tower structure of each corrosion period.In addition,the capacity curves of each model was obtained by Pushover analysis,and the limit state of each limit state of the structure was determined.The wind disaster vulnerability analysis of the structure was further carried out based on the above two analysis results,and the wind disaster vulnerability curve of steel transmission towers with different corrosion ages in the marine-industrial atmosphere in Ningbo area was established. |
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