26 February 2013

Kruunusillat bridge design competition: the entries (Part 2)

Okay, here's the second of three parts, continuing a quick run through the entries to this Finnish bridge design competition ... You can find more details on all the entries online, and there's a set of all the videos on YouTube. The first part is here.

Filum Lucis
I can see this design being unpopular with many of the people who tend to comment on architecture blogs and websites, but I like it. The bridge is a simple post-tensioned concrete box girder, cast in-situ, and intended to offer the most minimal line possible across the site, something which seems highly admirable when set against more attention-grabbing schemes.

Unda Arctica
This is one of my favourite designs, with a very elegant series of "undulating" arches, the arches above the bridge deck separated by reverse arches below the deck. Although that's visually attractive, it isn't structurally rational, with the reverse arches subjected to much higher bending loads than is desirable. Pedestrians and light rail are each allocated to once side of the deck, avoiding the separation of pedestrians into two streams that some of the other designs require.

In the previous post, I featured one design where the pedestrians and light rail vehicles were both tucked away inside a sheltering truss structure; and one where the light rail was sheltered inside the truss but the pedestrians exposed to the weather on an upper deck. Occursus offers a hybrid of these solutions, with the light rail on the steel truss's top deck, but pedestrians free to use either level, possibly according to the weather. I can't help thinking that most of these designs pay too much attention to the pedestrian users: this is a bridge over 2km long, which to me seems an excessively long, narrow corridor for walkers, although it's very suitable for cyclists. Won't most bridge users simply take the tram?

Septem Fratres
At first sight, this entry is very similar to Nexu, which I covered in the previous post. This one has seven central cable-stayed towers with 130m spans, while Nexu had six towers and 160m spans. The text for Septem Fratres describes it as an "extradosed" rather than "cable-stayed" bridge, which just means that the towers are of lower height and the cables at a shallower angle - it's a halfway house between cable-stayed and post-tensioned box girder bridge. The lower profile is one attraction, but I also prefer that on this option the main pedestrian route is all on one side of the bridge.

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