Fatigue assessment of structures on the Docklands Light Railway, London, UK

The Docklands Light Railway in London, UK has been in service for some 25 years and has now been upgraded for the second time to enable it to use longer trains at higher frequencies. The structures had to be assessed and, when necessary, strengthened. The assessment would normally have been done using a similar approach to that which would be used for a new design. However, this showed up a significant need for strengthening purely for fatigue. It was therefore decided to strain gauge some structures and the results showed significantly smaller ranges than predicted. Rather than use the results directly, they were used to develop a more realistic assessment approach. This was partly because of the need to apply results for a limited number of structures subjected to two-car trains, to a larger number of structures subjected to three-car trains. Comparison with the strain gauge readings suggested the adopted approach was still very conservative but major savings were still made compared with the strengthening that would have been required by the conventional approach. Two of the structures had more specific and localised problems. Here it was possible to strain gauge all the critical elements and more direct use of the results was possible.