The footbridge (pictured right) crosses Stirling Railway Station, and provides access between the new Forthside development and the town centre.
Designed by Wilkinson Eyre and Gifford, and built by Edmund Nuttall, the new bridge comprises two 88m span inverted Fink trusses, in an unusual arrangement that makes the bridge significantly different to the only other major bridge of the same form, the Royal Victoria Dock footbridge, not to mention unbuilt designs such as Flint and Neill / Exploration Architecture's Perpignan Bridge (shown below in colour) or Mott MacDonald / Knight Architects' River Douglas Bridge (shown below in black-and-white).
The trusses are assymetrical, being higher at one end than at the other, and each truss decreases in height in the opposite direction (see extract from planning drawing on the right), such that the bridge deck is supported on each edge by a propped cantilever - but with the cantilevers in opposing directions such that there is presumably a marked tendency in the deck to twist (dealt with structurally by making the deck a flattened box girder). The inverted Fink truss is inherently inefficient, and the assymetric arrangement will have added to that, as does the fact that the trusses aren't in a vertical plane, but incline outwards from the deck at an angle which warps along the deck by 35°.
All this adds up to a bridge which is exceptionally complicated geometrically. The justification for this comes from the wish to cradle the walkway in a manner which visually echoes the pedestrian desire lines (which are at an angle to the bridge span). From the photos and images currently available, I think it's an exciting design, taking a simple structural idea and playing with it in a very interesting way. It's especially nice to see such an innovative bridge resulting from the much-maligned Design-and-Build approach, often seen as a source of poor design quality.
The bridge is 113m long overall, so for those who pay attention to such things that's a cost of £57,500 per metre length. Assuming the bridge to be typically about 4m wide (actually it varies, but the clear useable width at midspan is certainly less than 4m - see planning drawings), that's a cost of over £14,000 per square metre of deck. This is high even by the usual standards of landmark bridges (a range of £4,000 to £7,000 per square metre was about right just a couple of years ago), so Stirling Council could have had an attractive, albeit less remarkable, structure for far less.
The delays completing the bridge have been attributed by Nuttall to the complex stressing sequence required, as well as the need to verify cable connectors supplied without proper testing. The difficulties of building such a highly assymetrical structure were alluded to in a technical paper by the designers [PDF].
Overall, it's one of my favourite Wilkinson Eyre designs of recent times, and likely to be a strong contender for various design awards over the next year or two.
Updated 4 May 2009: added credit to Explorations Architecture for Perpignan Bridge, and higher-resolution image