Application of capacity design procedure for transmission towers

The issues of collapse of steel-truss transmission towers are addressed in the thesis. The collapse of\ud one or several consecutive towers causes loss of electricity supply. Consequently, a part of income\ud from energy supply may be lost. In addition, collapse of tower cause high direct costs of restoration of\ud transmission line. In the theoretical part of the thesis, the most frequent collapse patterns due to\ud extreme action on conductors, as well as possible solutions for protection of the towers against\ud collapse are presented. The practical part of the thesis, which addresses electric transmission tower\ud NC74 of the 2 × 110 kV transmission line, involves definition of the design action according to\ud standard EN 50341-1 and redesign of critical elements of the existing tower on the basis of linearelastic\ud analysis. Follow nonlinear static analysis for sleet-based load cases, which represented the most\ud critical action for design of the tower. The results of nonlinear static analysis indicated that\ud overstrength due to redundancy of such towers is minor. The estimated overstrength of the tower is\ud thus primarily consequence of the utilization rate of the structural elements in the design. In the last\ud part of the thesis, capacity design procedure is applied to the transmission tower in order to prevent\ud global collapse of structure. The diagonals and the vertical elements of the tower were protected\ud against failure, whereas cantilevers of the tower were selected as week parts of the structure. In order\ud to meet this requirement, the diagonals and vertical elements of the tower were strengthened, and the\ud element of the cantilever, which had the largest utilization rate, was weakened by selecting smaller\ud cross-section of the structural element of the cantilever. This design procedure prevents global\ud collapse of structure for the price of increased mass of the structure, which was in this case\ud approximately 14% larger than that in the case of conventional design. For the application of the\ud proposed design approach in practice, a probabilistic analysis of the occurrence of the extreme actions\ud and the cost-benefit analysis should be performed in order to prove or disprove the economic\ud feasibility of the proposed design approach