CROSS Safety Report
Offshore tower failure
This report is over 2 years old
The top two thirds of a three part off-shore lattice mast failed due to problems with some of the connection bolts.
Key Learning Outcomes
For the construction team and design engineers
The need for collaboration over boundaries should be recognised where multiple parties are involved to ensure an assembled structure is considered as an integrated design
The transfer and coordination of relevant information is important to overcome interface issues as demonstrated in this report
Care is required to ensure that components procured from different suppliers are not designed in isolation
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The top two thirds of a three part off-shore lattice mast failed due to problems with some of the connection bolts. Initially it was not clear whether the bolts failed or came undone. At failure the resulting momentum of the falling section caused further damage to the remainder of the structure.
The mast had been regularly inspected. Although it was not confirmed as a cause of failure, it is believed by the reporter that the base had been designed for wave loading and the lattice tower had been designed for wind loading. The effect of wave loading on the dynamic response of the lattice tower, says the reporter, may not have been considered.
Following publication in Newsletter No 33 feedback was received as follows: ‘I am surprised there is no mention of fatigue failure of the bolts. I have experienced this on several structures subject to dynamic load where the bolts have not been properly torqued up to reduce cyclical loading.’ The response from the reporter was: ‘To the best of my knowledge, the bolts were not recovered. I agree with the comment but alas we do not have the evidence to comment further.’
Expert Panel Comments
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Care is required to ensure that components procured from different suppliers are not designed in isolation. The laws of physics will not respect contractual boundaries and so the assembled structure must be considered as an integrated design.
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