16 October 2017

German Bridges: 5. Crown Prince Bridge, Berlin

Ok, with the BAMPOTs out of the way, it's back to Berlin, and continuing steadily eastwards along the River Spree (the next bridge to the west is the Gustav Heinemann Bridge).

Santiago Calatrava has designed two bridges in Berlin. The Kronprinzenbrücke was completed in 1996, and is the result of a 1991 design competition. I may cover his other bridge later on in this series.

The previous bridge at this site had been demolished to reduce the number of East German refugees fleeing into West Germany. The Crown Prince Bridge was funded following German reunification and was presumably quite a significant symbol of the need to rebuild cultural and physical connections.

It's not a huge bridge - it's only 74m long, with a main span of just 44m. It carries a highway and walkways across the River Spree.

Calatrava's design owes something to his earlier (unrealised) Wettstein Bridge. It gives the appearance of being a skeletal steel arch bridge, while in reality being something different. The main bridge span is supported via lateral steel beams onto two "arches" running beneath the deck, and inclined outwards.

There's no a priori reason not to use vertical "arches"; the tilt is just typical Calatrava playfulness, part of an effort to generate a visually more dynamic geometry for the steel skeleton.

I put "arches" in quotes because on the face of it this actually appears to be a cantilever bridge, with Vierendeel trusses spanning outwards from the support piers, and given the illusion of arches by the adoption of shallow arch curvature. If these were true arches, the shallow curvature would lead to very high longitudinal thrust loads, and the support piers are not arranged in such a way as to resist those loads.

Instead, the piers are arranged to resist lateral thrusts, in line with the river. This is purely a function of the arch tilt, which is severe enough to put the piers into considerable lateral tension. It appears to be resisted by the very visible "knee" elements, but these just carry the loads into the interior of the lower concrete part of the piers. It's not visible to the observer, but inside the concrete there are large steel portal frames, which act as ties to restrain the lateral forces.

It's a "plinth" bridge of sorts, a visually attractive and interesting superstructure which is perched upon rather than integrated with its supports. The obvious way to resist the lateral forces at the piers is through a horizontal tie at springing level, but this spoils the purity of the superstructure's conception. The result, as with many Calatrava bridges, is that the substructure is forced to work unusually hard to allow the upper parts to remain unsullied.

As with Calatrava's better designs, much of the detailing of the bridge has been very well done. However, it's hard to tell how much of that is down to Calatrava and how much to other engineers charged with realising his design. Several details in the completed bridge differ from those in original design drawings (included in Frampton's book, linked below).

Look closely at how the arch spandrel elements are connected both to the arch and to a tubular deck girder, or at the shaping of the thrust supports on the bridge piers. The tilted parapets are attractively assembled, and the parapet ends are quite gorgeous, finely sculpted blocks which put so many other bridge designs to shame.

Shaped arch elements on the face of the abutments give an indication of load paths - abutments are too often blank, blocky and unattractive, but not here. This is particularly significant for a bridge which is experienced at close hand from the river side paths.

Not everything is great: the underside of the bridge deck is given texture and form by the exposure of a large number of ribs and service pipes, but it feels over the top to me. The upper chords of the Vierendeel trusses are also absurdly large compared to the lower chords - this appears to be solely so that pipes can be hidden inside.

Some considerable effort has gone into detailing the highway face of the bridge, with bespoke kerb lighting units and lighting columns. However, the curse of poor maintenance has left these looking forlorn, and in some cases damaged and corroded.

Nonetheless, I think this is on balance an interesting and attractive bridge, lacking in the overpowering and inhuman scale that ruins many of Calatrava's later projects.

Further information:

1 comment:

Anonymous said...

Calatrava forgot to design the bridge for boat collision impact. This was only realized very late, and caused a massive scandal. The bridge opening was delayed, and the two weathering steel deflectors were retro-fitted to deflect boats from hitting the piers, at great additional expense, and much bad publicity.
At the time, Calatrava had been selected as one of three finalists shortlisted for the Reichstag competition, and was the only architect proposing to put a cuppola back onto the Reichstag, but after the scandal of the mis-designed bridge, there was no chance that he would win, this had damaged his reputation too much. Foster won the Reichstag instead, and was asked to implement a cuppola similar to the one proposed by Calatrava.