In April, the winning design was made public for a new footbridge across the River Foyle in Derry, Northern Ireland. I didn't cover it here at the time but I've been looking at some of the design images, and it would be a shame not to feature it.
The bridge (which will cost £8.7m as part of a wider £13.3m project) is part of a regeneration scheme masterminded by ILEX Urban Regeneration Company.
The winning scheme is a design-and-build tender from contractor Graham, with design input from Faber Maunsell and Wilkinson Eyre. Their bridge is a 315m long, 4m wide self-anchored suspension bridge, curved in plan to follow an S-shape. The main span is 101m.
The construction cost works out at about £7,000 per square metre, which is pretty normal for a landmark footbridge and compares favourably with Wilkinson Eyre's new footbridge in Stirling (which costs twice as much). While you can't evaluate a bridge's merits solely on cost, value for money does matter, particularly for a regeneration project (the reality, however, is that most such schemes are not funded by the end-client, and scrutiny of value-for-money is generally absent).
The bridge has obvious echoes of one of Wilkinson Eyre's earliest bridge designs, the South Quay Footbridge in London, which shares the S-shaped plan and inclined masts, but was a cable-stayed rather than suspension bridge.
ILEX state that bridge construction will commence in September 2009, to be completed in October 2010. That's an optimistic programme for a bridge which will be complex to design and difficult to build. Self-anchored suspension bridges are a relatively rare choice, as unlike the more popular conventional suspension bridge (or the cable-stayed option), they are not structurally self-supporting until the deck and all cables are complete. This is because the main cables rely on the deck to anchor them. In contrast, a cable-stayed bridge can be built in segments, and a normal suspension bridge can have the cable completed in advance of the deck.
The consequence is normally a need for substantial temporary support within the river, and for a bridge with unusual geometry such as this one, more careful consideration of the cable connection and stressing requirements, and associated deck precamber.
The bridge form is envisaged as a "handshake", whereby two separate self-anchored structures are overlapped at midspan, and I think it's a very attractive design. The curves of the suspension form are softer and lighter than a cable-stayed solution would have been, and it also allows the overall height of the bridges to be lower and less overbearing.
There were four other tenderers, but I haven't seen details of any of the losing designs. If any become available (or are sent to me at happypontist at googlemail dot com), I'll post them here.