The Dynamic Reliability Of Transmission Tower System Under The Wind Load

The electric transmission tower-line system belongs to the Life-line system. The damage of transmission-line system can influence the industry in all fields and people's daily life, directly or indirectly. Therefore, it is essential to make sure that the electric transmission towers work well.Electric transmission tower, as a kind of high-rise, large-span structures, is very sentitive to wind load. Each year, there are lots of towers were disrupted by wind. So this thesis focused on the research of transmission towers, the response and the dynamic reliability of electric transmission towers under the wind load.In Chapter Two, The paper overviews the researches on extreme wind speed model. The main intent of this paper is to illustrate and compare the impact of methodological differences on extreme quantile estimates of wind speed and application of the each method. I contrast extreme values of wind speed distributions including Gumbel, Frechet and Weibull, Peak-over- threshold method (POT), method of independent storms (MIS) and The R largestest order statist (R-LOS) to wind speed and analysis the differences in quantile estimates and parameter estimation. Moreover, I illustrate character of each method like limitation, fitness, advantages and development. Gumbel distribution is often used in many national codes with a little bigger result than the actual wind speed and POT is sensitive to thresholds. Moreover, several methods like the method of moment (MM), the method of maximum likelihood estimation (MMLE) and the least-square Method are mentioned to estimate the parameters of distinguished models.The next chapter discusses the simulation of wind, especially the time series of turbulent wind speed are simulated by Weighted Amplitude Wave Superposition (WAWS). Seventeen groups of trubulaent wind speed along the one tower for each design return period, is done under the environment of software, MATLAB 6.5. That means that totally 272 groups of turbulent wind speeds are simulated.The model of electric transmission tower is demonstrated in Chapter Four. The model are simulated by the SAP 2000. The results of modes and along-wind responses of electric transmission towers are calculated in time domain.The final chapter demonstrates the reliability of transmission tower under wind load in three aspects: Stiffness reliability, Strength reliability and fatigue reliability. The first two aspects apply the First-Excursion Theory. So called the First-Excursion theory is improved here in the field of dynamic reliability, including the reliability under different design return periods and different models: In-line System Model and Top-simplified Model. Furthermore, the results are compared and get the conclusion. The final aspect adapts the theory of cumulative damage to calculate the fatigue damage, fatigue life and reliability.