The weight of water
On 18 October, two rail commuters were ‘lightly’ injured by a deluge of rainwater after a roof ‘cushion’ ruptured at Manchester’s Victoria railway station. The £20 million roof over the tracks, recently installed as part of a wider £44 million revamp of the station, consists of ethylene tetrafluoroethylene (ETFE) cushions supported by a steel frame.
The cause of the incident is under investigation, but the Beleben blog would posit that if rain were somehow able to enter some of the cushions from above, the weight of water build-up would cause their lower membranes to distort, and eventually give way. The ETFE film is very light (and very thin), which ‘reduces the amount of steelwork required’ (compared with glass).
Presumably, in wintry weather conditions, there could be a build-up of snow on the topside of the roof, which might lead to a much worse outcome.
On the information available to the Beleben blog, there was no need to demolish the old roof to enhance or modernise the station.