Thank you, that's very helpful and comprehensive. I think I've now worked out why I have been mildly confused about all of this; Prince's Bridge, which was a road bridge, was also designed by Stephenson and first erected in 1830
http://manchesterhistory.net/manchester/tours/tour1/princebridge.html
But can anyone tell us more about why, according to the plaque referred to there, it had to be "re-erected" in 1905?
If so, thanks!
An 1830 metal bridge (if that's what it was) would be quite likely to need replacing by 1905. At a guess, Stephenson's original Prince's Bridge needed replacing, either through being decrepit, narrow, or unsuited to 20th century traffic, and was rebuilt to a different design or of modern materials. Maybe "re-erected" is a euphemism.
The bridge that has now been demolished was not listed. This page credits it to James Gascoigne Lynde and does not mention the Stephenson bridge it replaced:
http://www.manchesterconfidential.c...w-of-the-week-irwell-street-bridge-and-beyond