Reliability assessment of existing transmission line towers considering mechanical model uncertainties

Abstract

Reliability assessment of transmission line towers (TLTs) becomes particularly important in the context of the growing demand for increasing the energy transport capacity of existing lines. However, a comprehensive literature survey in this field reveals that important discrepancies may exist between the original design model analysis results and the actual lattice steel tower behavior. For instance, it has been demonstrated (Kaminski-Jr, 2007; CIGRE, 2009; Souza et al., 2019, 2020) that bolt slippage effects, which are disregarded in the current industrial practice, is importantly impacted by the tower topology that is defined by the tower engineer based on experience. Therefore, because several existing structures have topologies prone to connections’ slippage, they may be operating with a lower reliability when compared to modern recommended values. Within this context, the main goal of this paper is to assess the structural reliability of existing TLTs considering mechanical model uncertainties induced by connection details. For this purpose, the failure probability of two real TLTs built in Brazil are investigated employing different levels of structural modeling complexity. The first tower was designed 40 years ago and, several TLs operating in Brazil have adopted a similar design. The second is a newer structure, designed 15 years ago. In addition, to better understand the impact on the results when following the classical design procedure, the progressive collapse of both TLTs is modelled through a full material and geometric nonlinear analysis with and without the consideration of bolt-slippage effects. The results show that the older tower design, which presents a topology highly impacted by bolt slippage, is associated with a lower reliability than the current target values.