28 October 2009

Copenhagen bridge competition winners

Flint and Neill and WTM Engineers have been declared winners of a bridge design contest in Copenhagen.

The contest was in two parts: a 9.4m euro opening footbridge spanning 50m across the Inderhavnen (Inner Harbour), won by a design from Flints with Studio Bednarski; and further footbridges spanning Christianshavns Kanal and Trangraven, and across Proviantmagasingraven, won by a design from WTM with Dietmar Feichtinger Architects. There were eight other entrants, with many of the big names in landmark bridge design represented.

The new bridges provide improved walking and cycling links including to the recently completed Opera House. Their construction is being funded privately by the A.P. Møller and Chastine McKinney Møller Foundation, and they are expected to be completed in 2012.

The Inderhavnen structure has already been nicknamed the "kissing bridge" (see right, and below, click on images for larger versions). The two moving halves of the structure retract and extend longitudinally on support rails, like twin brachiosaurs bumping noses when they meet in the middle.

Retractile bridges are very rare, and this bridge will be a nearly unique structure when built. The point of support of the moving span continuously changes as the bridge opens, which normally makes the supporting structure over-heavy compared to a bascule, swing, or lifting bridge, where the reactions are generally carried directly at a bridge pier. Maintenance of the tracks may also be a concern, and the bridge will also be slower to operate than alternatives, as the main spans have to be jacked off their main supports onto the rolling tracks before operation. The jacks, and the interlocking mechanism required at midspan, all add to the likelihood that the bridge will be more expensive to maintain than alternative options. [But see Update below!]

Most retractile bridges are floating structures, where this isn't a problem, and where they can provide larger opening spans than the alternatives (as at the Hood Canal and Ford Island bridges).

In favour of the retractile bridge, the energy costs for operation should be less than a bascule, as the wind loads are much lower. And of course, it will look pretty cool.

The WTM / Feichtinger bridges (see right), which cross smaller arms of the harbour canals, are more conventional single-leaf and double-leaf bascule structures. These have no significant counterweight elements and appear to be supported in both open and close positions on their main hydraulic cylinders, a situation which is far from ideal. Although they're relatively minimalist in appearance, they seem somewhat unconvincing to me.

Several of the other entries are well worth a look, and you can find them online in the jury report at the Copenhagen Kommune website [PDF]. Regretably, I'm a bit too short of time right now to give them a thorough analysis here, but the jury report has plenty of detail on each design. The decision to publish the jury report is something that other competition organisers could learn from: the entrants (all ten of whom were paid a fee for their efforts) receive useful feedback; the scoring process is clearly set out; and the whole exercise is seen to be transparent and rational.

Updated 30 October: Since writing the above, I've been advised that some of the technical details given in the jury report for the Flints design have been changed during the negotiating stage of the contest. In particular, some of the operational aspects have been altered, such that the maintenance costs are likely to be less of an issue than I suggested above. Hopefully more details of the final design will become available in due course.

From the wider perspective, this willingness to fine-tune the design is another example of how sensibly the Copenhagen competition process has been arranged, compared to other cases where a design vision is seen as fixed on day one, despite the limited amount of time a competitor has been given to prepare it.

1 comment:

Anonymous said...

I agree that the organisation and judging of this competition is exemplary. The jury comments demonstrate a sound understanding for technical and cost issues and they have a clear feeling for the urban and architectural aspects of the canal setting. What a difference from the chaotic competition process in the UK! Was there a prize fund for the shortlisted and winning teams?