The application of probabilistic methods and reliability theory to the design and analysis of electric transmission lines has gained recognition among the professionals as it offers a methodology to systematically study the probability of non-performance of these complex structural systems considering the uncertainty associated with all the variables involved in the definition of limit states. Operational experience with transmission lines highlights climatic hazards as one of the principal causes of overhead tower failures. The inherent randomness of climatic variables such as wind direction and speed and of the structural capacities of components has a major effect on the failure probability of transmission towers. The objective of this paper is to develop a reliability model using response surface method to assess the structural reliability of typical overhead towers, considering the randomness of these climatic variables and of the resistance of structural elements. The Response surface method is applied to implicitly determine the limit state function for each component of the tower through repeated structural analysis of the overhead tower under various combinations of climatic events. Therefore, a Visual Basic code is developed to prepare a three dimensional model of a two span transmission line section in the structural analysis software SAP2000. As the approximate limit state function is determined, Monte Carlo simulation can be used efficiently to assess the component and system reliability of the overhead tower since the evaluation of the response surface function requires very little computational effort.
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