Thanks to the New Civil Engineer, some light is shed on how Gifford's competition-winning Foryd Harbour design actually works. I previously speculated that this £4m opening footbridge might be a drawbridge, and indeed that's exactly what it is, although not in the conventional manner.
The design goes big on durability, with the pylon being made from stainless steel, and the lifting bridge decks from glass-reinforced plastic. It's not clear whether all parts of the decks are GRP, but the images released so far suggest they might be entirely GRP, in the manner of a fibreglass boat hull. I gather that minimum maintenance was a key issue for the bridge's promoter, Denbighshire County Council, so it's easy to see how this scored well, especially against the competitors (which I'll be showing here shortly).
These features alone make it a highly innovative design, and it's nice to see that emerge from the often conservative design-and-build route. However, it's equally easy to see it as risky and the sort of thing likely to prove a challenge technically, financially, and in achieving the desired programme.
The other unusual feature is that the drawbridge cables aren't spooled directly (as on castle moat drawbridges), but attached to a ring which moves up and down the pylon (presumably via a separate cable system). I'd be happy to be told otherwise, but I believe this would make the design unique. Again, while admiring the pioneering spirit, I can see all the risks and issues, and wonder what the judging panel made of them: how are lightweight GRP decks stable against wind when they're raised? How well does the ring operate when the cables attached to it pull it to one side under wind? How reliable is the mechanism generally?
If I were a betting person, I'd predict now that this design will prove problematic: it will fail to fit in the client's £4m budget, be completed on time, or prove unreliable in service (always a risk with new prototypes, especially for an opening bridge). I'm not a betting person, so I wish the designers the best of luck in avoiding the pitfalls!
I've got together three of the four other shortlisted entries, and hope to feature those here in about a week's time. They should make for a very interesting comparison.
As an aside, there's a letter in the same issue of NCE which praises Techniker's River Wear design (discussed here on several occasions last year) as an example of what engineers should aspire to aesthetically. It's deeply depressing that letter-writing engineers, who presumably learnt their bending moment formulae like the rest of us at college, are taken in by the superficially attractive styling of a design like River Wear, and are seemingly blind to the exceptionally challenging structural behaviour that it relies on. As noted previously, there's a need to teach civil and structural engineers to think more critically about design, and this letter just reinforces that need.