A study of the low-cycle fatigue failure of a galvanised steel lighting column

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Alexander, L.A. and Wood, J. (2009) A study of the low-cycle fatigue failure of a galvanised steel lighting column. Engineering Failure Analysis, 16 (7). pp. 2153-2162. ISSN 1350-6307 (https://doi.org/10.1016/j.engfailanal.2009.02.012)

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Abstract

This paper presents the results of a low-cycle fatigue test on a galvanised steel lighting column. The aim of the test was to simulate the behaviour of the column undergoing large amplitude resonant vibration caused by wind. A metallurgical study of the failure revealed the significant role of the galvanised coating in the failure process. Results from a detailed 3D finite element model are also used to explain the failure mechanism. The swage joint in the column was confirmed as a failure location by both experiment and finite element analysis. This in itself is not surprising and the position of the fatigue failure is consistent with those observed in the field. Of more importance is the fact that the experiment shows that galvanizing can lead to premature failure of such columns. This is a highly significant conclusion as it implies that improving the weld detail in an effort to improve fatigue life may be ineffective for lighting columns coated in this manner. Given the detrimental effect of galvanizing on fatigue performance and the fact that the most severe corrosion will be on the outside of columns, then the fatigue life of such structures may benefit if the inner surface was not galvanised in high stress regions. An alternative improvement would be the use of a galvanizing coating with higher toughness and less susceptibility to cracking and damage. Attention is drawn to the need for a better understanding of the fatigue performance of galvanised steel columns resulting from large amplitude wind induced resonant vibration. The approach adopted so far for lighting column resonant vibration, has been to try and avoid it. While this is a laudable objective, clearly this has not always been possible, as designs push the limits permitted by Codes of Practice.

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