Reliability Analysis Of A Transmission Tower Under Typhoon Loading

As a direct structural support of electric transmission line,transmission tower directly affect the reliability of transmission line.The wind load defined in current transmission line design code,is based on the characteristics of monsoon wind.In recent years,more and more transmission towers collapsed due to typhoon.The reliability of transmission tower under current design standard may not be sufficient.Therefore it is necessary to check the reliability of transmission tower under typhoon loading,and to provide the basis for improvement of transmission tower design.In this thesis the structural reliability of a transmission tower under typhoon loading is studied.The researches of the engineering characteristics of typhoon in literature are summarized.And this paper focuses on the vertical wind profile model,wind profile coefficient,gradient height and turbulence intensity,which are the main factor that affect the calculation of equivalent static wind load.The formula to calculate the wind profile coefficient and turbulence intensity of typhoon are obtained,which can be used in the southeast coastal area of China.The wind load calculation in transmission line design code is improved,and the equivalent static typhoon loading of transmission tower is obtained.The mine failure modes under monsoon loading has been identified by branch and bound method of critical strength for the local system.Using ANSYS software,an analytical model for a typical 220 k V transmission tower is established.By branch and bound method of critical strength for the local system,two failure modes under monsoon loading and typhoon loading are identified.The difficult problem that how to identify failure modes of large bar structures rapidly and efficiently in ANSYS,has been solved in this paper.By comparing the weak position,failure path and failure criterion of transmission tower under two kinds of wind loads,the failure mechanism of transmission tower under typhoon loading is obtained.The reliability probability of a transmission tower under typhoon loading is calculated by combining the Monte Carlo method and the PNET method.Based on the probability analysis file of ANSYS,the probability of failure modes of transmission tower is calculated using Monte Carlo method.Finally,the system failure probability of transmission tower is calculated by PNET method.As a result,the reliable probability of a transmission tower under monsoon loading and typhoon loading is given respectively.