Model uncertainty in the assessment of transmission line towers subjected to cable rupture

Model uncertainty affects all stages of structural reliability analysis, from the description of loads and the system itself to the process by which the effect of loads on the system is evaluated. The last issue has been largely ignored in the previous developments in the field, in part due to its elusive nature. A study conducted by CIGRة on transmission line (TL) towers subjected to static loads, among other exploratory assessments, demonstrated that mechanical model uncertainty was a relevant factor and could not be disregarded. The issue, in which attention is focused in this paper through the study of a specific problem, may significantly influence the outcome of reliability assessments. The dynamic response of latticed TL steel towers subjected to cable rupture is predicted by the use of various models with different degrees of sophistication or detailing. The predictions of the various models are compared with the aim of quantifying mechanical model uncertainty. In essence, the problem consists of evaluating the uncertainty in response predictions, once all parameters that define the external actions and the system itself have been unequivocally prescribed. Finally, possible ways to explicitly consider model uncertainty in reliability assessments and in code formulations are outlined.