| As the carrier of power transmission,transmission tower structure is an important lifeline project,and its safety performance is related to the normal operation of overhead transmission line.Therefore,It has important theoretical significance and engineering value for reliability analysis of transmission towers.At present,a lot of theoretical research on transmission tower has been carried out by scholars.The research shows that The truss model established by the Transmission Tower Analysis Program(TTA)which is usually used by the Domestic Electric Power Design Institute cannot fully reflect the internal force variation characteristics of the tower,the structural calculation model established by using beam elements to simulate the main material and rod elements to simulate the auxiliary material based on ANSYS program is more consistent with the actual situation of the iron tower;The current research on the reliability of transmission towers mainly focuses on the reliability analysis of the ultimate state of bearing capacity under the load conditions such as high winds,ice cover and foundation settlements,and the research objects are mostly straight-line towers.Research on the reliability of corner towers,which are also an important part of transmission lines,are rare at present.The transmission towers are usually hyper static structure which are extremely sensitive to uneven settlement of the foundation.However,with the development of the power industry,there are still a number of transmission line projects that have to be built in areas with relatively poor geological conditions.Therefore,it is necessary to carry out reliability analysis under the tower bias condition caused by uneven foundation settlement.This article is based on the transmission line corner tower(Code 1XZB2-SJC4)of the Luolong-Bianba 110kv line in the Tibet region that the author participated in during the internship of Hunan Electric Power Design Institute.The following work was carried out around this transmission angle tower:1.Based on the data of the Transmission Tower Analysis software(TTA),tower truss-beam hybrid finite element model was established by using the general finite element software ANSYS.The internal forces of the ANSYS model and the TTA model under normal operating conditions were compared and feasibility of truss-beam hybrid finite element model was validated.On the basis of the finite element model,the internal force analysis and displacement analysis under the wind conditions with the design wind speed were carried out.2.Taking into account the main factors of this project’s seasonal frozen soil,as well as the collapse of the transmission tower along the slope may appear wet geological and geological disasters considering the main working conditions such as gravity load,wind load,and differential foundation settlement,a response surface reliability analysis method combined with Monte Carlo sampling was adopted to perform reliability analysis and safety assessment of the transmission tower under uneven foundation settlement.3.The modal analysis of the tower was performed by using the Lanczos method(Lanczos).The transient response analysis module of ANSYS was used to analyze the dynamic response of the transmission tower under uneven settlement conditions,and the influence of damping ratio and differential settlement rate on the dynamic effect of the tower were obtained.The finite element numerical simulation results show that the truss-beam hybrid model established in this paper can well replace the truss model established by TTA.Through the analysis of internal forces under strong wind conditions,the most unfavorable position of the tower stress is generally found at the position of the tower leg,and the displacement of the superstructure is sensitive to the wind load.At the same time,the reliability analysis results show that the uneven settlement limit value given by current technical requirements for this type of corner tower was not applicable.The response surface equation established by MATLAB shows that the uneven settlement limit of the angle tower should be controlled at 0.0015B(B is the root of tower)to meet the reliability requirement for normal use of the tower;dynamic analysis results show that the natural vibration period of the tower meets the requirements of the Design Code.The larger the damping ratio,the more unsafe the structure.The shorter the duration of foundation settlement is,the more obvious the dynamic response of the tower is.When the holding time exceeds a certain degree,the dynamic coefficient will basically tend to be stable. |
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