22 December 2017

Karlín Holešovice bridge design competition, Prague

Many thanks to a reader for drawing my attention to this footbridge design contest in Prague.

A previous competition was held for the same site in 1999, but flooding in 2002 led to the winning design being taken no further. Significant changes to riverside flood defences required a higher clearance to the river.

The present competition was announced in April this year, with a winner declared on 4th December. Intriguingly, a 3rd prize and two runners-up were also declared, but no 2nd prize!

There were nearly 50 submissions, with entries including one or two "big names" in the field, but mostly locals. I've included details of the prize-winning entries here, and you can visit the project site to see all the other submissions.

There's a clear contrast with the last open footbridge design contest I covered here, the Nine Elms - Pimlico Footbridge. The Prague contest features a lot less of the "arty bollocks" that was seen in London, and I wonder how much of that is down to how the contest was organised, including the nature of the prize money, and how much is a cultural thing.

Ing. Marek Blank, Ing. arch. MgA. Petr Tej, with Ing. Jan Mourek, Janek Srnka, Ing. Jiří Hejzlar
The winning design is a 300m long white trough, made out of precast UHPFRC units prestressed together. The longest span is 84m, and the trough is 1.6m deep, which feels a little on the slender side, but feasible given the ability of UHPFRC to carry very high levels of prestress compared to conventional concrete. I guess that following the recent collapse of the Vltava River footbridge in Prague, authorities may now have second thoughts about a prestressed design.

I have mixed views on the visual merits of the design: I admire the minimalist aesthetic, but it feels too much like a channel intended as an aqueduct, rather than as a footbridge.

3rd Prize
Ing. arch. Lukáš Landa, Arch. Pavel Rak, with Ferrari Gartmann AG
This design chooses shorter spans, with a longest span of 55.5m. The structure is shown comprising twin steel box girders, each 0.9m deep, composite with a 0.15m thick concrete deck slab. Very slender support piers are shown, with rocker bearings at the top, so perhaps these are hinged top and bottom to allow thermal movement.

It's a simple, reasonably elegant design, but leaves me wondering why you would run a major design competition just to choose something that's so close to bog-standard.

Petr Hájek Architects
This entry is one of the most interesting in the contest. The bridge is a quite industrial looking truss structure, which on its own would seem quite inappropriate. The attention-getting feature is a series of pedal-operated gondolas slung below the bridge, intended to transport heavier goods, or to create platforms for anglers. It would have been remarkable if this had won, but it's nice to see some imagination being applied and appreciated.

Association of Architects - Jurák, Filsak
The other runner-up is also very different from the majority of submissions. It creates the most open and lightweight bridge deck possible, by suspending it from a pair of parallel girders overhead, which appear to be built from weathering steel. Let's face it, who wouldn't want to cross a river on what feels like gently swaying scaffolding hung from giant ribs of rusting metal? I certainly would, if only to admire the graffiti it would inevitable attract.

The remaining entries are well worth spending a few minutes (or hours) skimming through, just to see the impressive range of effort that has been brought to bear. The quality is generally good (although rarely excellent), perhaps indicating that central/eastern Europe still takes engineering seriously (unlike the west of Europe, where it is sometimes seen by architects as an afterthought).

No comments: