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:

14 October 2017

Bridge Awards for Mediocrity and Plain Old Terribleness - The Winner!

I announced the Bridge Awards for Mediocrity and Plain Old Terribleness (the BAMPOTs, for short) back on 3rd September. Twenty-two bridges were nominated by the blog's readers, and passed to a panel of bridge experts to produce a shortlist of the worst of the worst, which was announced on 1st October. The shortlist was opened up to a final public vote.

This convoluted process is of course just a way of getting myself off the hook ... I didn't nominate, shortlist or vote for any of these bridges, so don't blame me!

Anyway, the votes are in, the counting is done, and we have a winner!

Seventy-three people voted. In reverse order, the votes are as follows:
  • Arch footbridge near Exeter, UK: 7 votes (9.6%)
  • Cumberland River Bridge, Nashville, USA: 8 votes (11.0%)
  • Lucky Knot Bridge, China: 13 votes (17.8%)
  • Seabraes Footbridge, Dundee, UK: 15 votes (20.5%)
  • Millennium Bridge, Ourense, Spain: 30 votes (41.1%)
So what can be said about a bridge which won over two-fifths of our discerning audience (and, incidentally, which was unanimously the worst rated bridge by the judging panel)? (All photos courtesy of Victor Hermida Prada).

The nominator was anonymous, and said: "My vote goes to: Millenium bridge... in Ourense, Spain. I don't think it needs much explanation, just type 'puente del milenio ourense' in Google and the images will make clear why!"

A comment on Twitter is also illuminating regarding the context for the bridge:

The judges said: "I will never understand the 'creative mind' that came up with this. It has more than a smack of 'emperor's new clothes' about it" ... "Exquisite in the dictionary sense meaning 'piercing, excruciating, agonising, harrowing, tortuous, tormenting'" ... "It has everything: Absolute lack of respect for the valuable collection of historic bridges in the city, a deck depth that makes any other structural help unnecessary, lots of unnecessary structural help, inclined pylons (verticality is overrated) that lead to clumsy over-designed piers that try to relate to the inclination."

I think it is undeniably an awful bridge, and well deserving of recognition as this year's top BAMPOT. I'd echo all the comments from the third judge above - its largest offence is its ungainly combination of multiple geometries, none of them designed well in their own right, and worse when plastered on top of each other. The walkway gimmick gives the initial impression of being a suspension bridge, but instead it's the killer garnish that overpowers everything else.

It's a hard bridge to look away from, but only in the same sense as a car crash. I'd certainly love to visit it, and indeed the Ourense tourist office promotes it as a significant attraction, along with their other bridges.

I'd like to thank everyone who nominated or voted for the BAMPOTs, and particularly the judging panel who showed sound judgement and also impressive endurance.

What do others think? Is the Ourense bridge a worthy winner? Do you think one of the other bridges should have won, and if so, why? Please use the blog page comments feature to provide feedback!

04 October 2017

German Bridges: 4. Humboldt Port Railroad Bridge, Berlin

Taking a little detour, we continue east along the River Spree from the Gustav Heinemann Bridge, and then turn north into the Berlin-Spandau Ship Canal. The channel opens out here into the wide Humboldt Harbour, and is spanned by several railway tracks just to the east of Berlin Central Station.

The Humboldt Port Railroad Bridge, or Eisenbahnüberführung Humboldthafen, as Structurae has it, was built in 1999. It carries a significant stretch of railway - from here you can apparently travel to Paris in the west, or to Moscow in the east.

The design contract was awarded to Architekten von Gerkan, Marg und Partner, working with engineers Schlaich Bergermann. The contractor's engineer was Leonhardt Andrä und Partner, while Krätzig und Partner acted as expert review engineer.

The 240m long bridge supports six tracks, and varies in width from 40m to 66m to accommodate the track layout on the station approach. This section is part of a longer series of railway viaducts around 1km long in total.

The bridge comprises prestressed concrete "T-beam" decks, 1.7m deep and spanning up to 25m onto steel column supports. Over the harbour there is a single 60m span, comprising steel arches. There are three viaducts running alongside each other, each curved in plan.

The arch ribs are steel tubes 660mm in diameter, made from 100mm thick plate. The detailing where the tubes support the deck is odd: there seems to be a thin concrete platform immediately below the main deck girders, with this platform element compressed by the arch tubes so that it forms part of the arch structure.

The bridge has pinned articulation at the supporting arch nodes, and also some of the tubular column supports.

The connections between steel tubes are made in cast steel, something rarely seen in bridge construction, and claimed here to be a first on a rail bridge (its use on a footbridge can be dated back at least a decade before).

Cast steel is usually seen as expensive, although is increasingly common in large buildings where the structural members are visible. It has considerable advantages over welded steel with regard to fracture resistance and fatigue, especially as sharp corners can be easily eliminated.

For the Humboldthafen Bridge, finite element analysis was validated with physical testing at the University of Karlsruhe, using tubes up to 508mm diameter and with walls 50mm thick.

I don't think it's an especially beautiful bridge. There are individual elements with nice detailing, but the junction of the arch and deck is very awkward, the two structural forms are superimposed rather than integrated. The hinges at the column bases and arch springings are not well expressed, and there are inconsistencies in the different types of cross-bracing applied. I'm not sure the cast nodes add a great deal visually, either.

Where it is successful is in how it unifies the arch and beam/column parts of the viaduct, a combination of systems which could otherwise have been very disjointed visually.

Further information:

02 October 2017

German Bridges: 3. Gustav Heinemann Bridge, Berlin

For now, I'll keep heading east along Berlin's River Spree. After the Moltke Bridge, the next structure is the Gustav Heinemann Bridge (Gustav-Heinemann-Brücke), which was built in 2005.

The design was selected as the winner of a competition. The bridge was designed by architect Max Dudler and engineers Grassl and KLW Berlin. Lighting was designed by Designplan Leuchten. The bridge connects the forecourt of Berlin's central railway station to the various central government precincts around the Spreebogenpark. It is named after former President of West Germany, Gustav Heinemann.

The design seems to be a celebration of austerity. The two edge girders are Vierendeel trusses of constant depth and bay spacing, and the use of constant H-sections for all the members adds to the visual simplicity. The bridge is 5m wide, with wooden decking supported on steel cross-members.

The truss girders are 2.25m tall, but the centre-to-centre dimension is reported as 1.82m. The spans are respectively 9m, 66m and 13m, giving an effective span-to-depth ratio of 36:1, which is high even for a pedestrian bridge.

The two relatively short end spans help to "clamp" the centre span. The bridge deck is therefore tied down at its ends using hinge links, and sits on the intermediate support piers via elastomeric bearing pads. Tuned mass dampers are hidden below the deck to reduce vibration, and the bridge was vibration-tested by groups of up to 25 people during construction.

The deck level is raised relative to the bottom of the girders, presumably because otherwise the upper chord of the girders would be visually intrusive. The walkway is separated from the girders by a balustrade in the form of a metal grille.

The H-section configuration of the girders means that the outer and inner surfaces are a series of recessed boxes defined by the overlap of the chord and web member flanges. On the inner face, the lighting units are tucked away into the recess at the top of the girder webs.

The detailing is exceptionally simple, but I found it considerably more satisfying than the more normal hollow-section Vierendeel truss footbridge, which presents a featureless face to the world. The arrangement of the H-sections is logical in resisting in-plane bending moments.

For me, the colour is a slightly odd choice, being a grey-green with a slight hint of the military to it (see, for example, "Panzer Olive Green"). It's preferable to the conventional pale grey of so many bridges, but only just.

I can't quite work out what's going on with the timber flooring. There are five rows of bolt-heads clamping these to steel stringers running below. there are also two steel durbar plates, one on each edge. Can anyone tell me what these are for?

On the whole, I find this a bridge to admire rather than necessarily to like. Rigour and logic always have a certain appeal, but it's a blank, steely-eyed, inexpressive sort. I don't think a spot of real colour would have gone amiss, and the bridge geometry would have lent itself to something subtly Mondrianesque, perhaps.

Further information:

01 October 2017

Shortlist announced for Bridge Awards for Mediocrity and Plain Old Terribleness (the BAMPOTs)

Back on 3rd September, I invited nominations for the Bridge Awards for Mediocrity and Plain Old Terribleness, a.k.a. the BAMPOTs.

Twenty-two bridges were nominated in all, and I engaged the services of a secret cabal of high-powered bridge experts to evaluate each nomination, and prepare a shortlist of the worst examples. Each member of the cabal scored the bridges independently, and the shortlist is based on the worst average scores.

These were the 17 bridges nominated but just not quite bad enough to make the grade:

Many thanks to everyone who took the time to nominate these bridges! For further details of why they were nominated, see the comments to my original post.

The top five bridges have been shortlisted below, and I'll invite you, the public, to vote on which is the worst. See the end of this post for details of how to vote!

The nominator said: "But when you get to the end of the arch, all is revealed, or perhaps “nothing” is revealed ... The arch is mere decoration."

The judges said: "Crime of the century; a cross between blood curdling and blood boiling. There are all too many examples of bridges with decorative structure but somehow a false arch is a greater affront on natural justice than a cod cable stay or a suspicious suspension bridge" ... "Clearly the client had money to burn, what with the decorative arch and all" ... "The combination of a deep deck and a low-responsibility structure above it is something Calatrava has been doing for a long time, but the lack of connection between both in this case, pushes it to a further level."

The nominator said: "When you start with a box girder then change your mind to a suspension bridge".

The judges said: "An interesting combination of old-school suspension-bridge stone end-gates, pylons with bracing design inspired by the logo of a lodge, and cables that could be made with shoe laces" ... "My head hurts looking at this" ... "Belt,  braces and sturdy shoes with a Scottish heart and a Greek face. What's not to like?"

The nominator said: "This monstrosity should need little in the way of comment, but I will specifically draw attention to the way in which what could have been an interesting whimsy has been ruined by someone who can only draw with a super-fat pencil; and the absence of any step-free access, inexcusable in such a major crossing regardless of the local culture".

The judges said: "An awful bridge that has managed to make its grim surroundings look quite attractive by comparison" ... "Great stuff! The materialisation of the napkin sketch of an obvious easy-selling idea. But it is much more than this, it also includes multiple walking routes (none of them accessible for disabled people, but maybe there are no disabled people in Chinese megacities), gigantism, and a bright red colour to piss you off in case you don’t like it."

The nominator said: "My vote goes to: Millenium bridge... in Ourense, Spain. I don't think it needs much explanation, just type 'puente del milenio ourense' in Google and the images will make clear why!"

The judges said: "I will never understand the 'creative mind' that came up with this. It has more than a smack of 'emperor's new clothes' about it" ... "Exquisite in the dictionary sense meaning 'piercing, excruciating, agonising, harrowing, tortuous, tormenting'" ... "It has everything: Absolute lack of respect for the valuable collection of historic bridges in the city, a deck depth that makes any other structural help unnecessary, lots of unnecessary structural help, inclined pylons (verticality is overrated) that lead to clumsy over-designed piers that try to relate to the inclination."

The nominator said: "I have real doubts about this one."

The judges said: "A camel is a horse designed by committee" ... "If you had left a three-year-old playing with a bridge catalogue you would probably have got a more logical result" ... "Interrupted arches, stupid structural scheme combination. Works like this one are the reason why some people hit their foreheads with the palm of their hands when they are told that an architect will be involved in the bridge project they will be working on."

How to vote
You have until midnight (UK time) on Friday 13th October, to vote here.

30 September 2017

German Bridges: 2. Moltke Bridge, Berlin

Heading east along the River Spree, the next bridge is Moltke Bridge (Moltkebrücke).

This is a bridge with a history. A timber swing bridge was constructed here in 1850/1851, but replaced with a multi-span wrought iron arched bridge in 1865, the Unterspreebrücke. That bridge only lasted until 1886/1887, and the present highway bridge was then built in its place, completed in 1891. The bridge is named after Prussian military commander Helmuth von Moltke, who died shortly before the bridge was finished.

The structure was designed under the direction of city architect Otto Stahn, who designed several of Berlin's bridges, most notably the famous Oberbaum Bridge. Stahn worked with urban planner James Hobrecht.

The bridge was the site of a battle between Russian and German forces in 1945, with the Germans detonating charges which damaged but did not completely destroy the bridge. The structure was rapidly restored after the war, with some masonry parts replaced in concrete. A comprehensive restoration took place from 1983 to 1986, including the insertion of structural steel strengthening members.

The casual visitor today would have little idea of the bridge's difficult past. Perhaps the biggest clue is the good condition of the sculptures and red Main sandstone carvings, many of which are replacements for damaged or lost originals.

It's no longer in fashion to decorate bridges in this way, which I think is something of a shame, as it links a bridge to the wider culture, and locates it as part of history. The Moltke Bridge is very well decorated, with carved faces above the crowns of the arch (the grumpy one pictured here is apparently Moltke himself), statues above the pier cutwaters, and carvings and statues at either end.

A damaged statue sits on the north river bank to one side of the bridge: I understand this has been left as a deliberate reminder of the damage that can be caused by war.

The various sculptures were originally designed by Johannes Boese, Karl Begas and Carl Piper, with the restorations by August Jäkel. I like the decoration on the bridge: it's dignified and slightly over-done, but neither gaudy nor kitsch.

Further information:

27 September 2017

German Bridges: 1. Chancellor's Bridge, Berlin

While I was in Berlin recently, I took the chance to visit a number of the city's bridges. A boat cruise along the River Spree provided a prelude to the Footbridge 2017 conference dinner, and I revisited a few of the more interesting bridges as well.

The first of these, the Chancellor's Bridge, or Kanzlersteg / Kanzleramtssteg, is a private pedestrian bridge built for the sole use of the German Chancellor's office and its visitors. The Chancellery sits on the south bank of the Spree here, and is an expansive and to my taste lamentably post-modern establishment, which dwarfs the facilities of the heads of government of many other states (cf. 10 Downing Street or the White House, which are a fraction of the size). The bridge provides exclusive access to the Chancellor's park (and helicopter landing pad) on the north bank. It is only accessible to the public on an open day once a year.

The bridge was completed in 2000, and is a three span structure with spans of 20m, 85m and 17m. The superstructure is of steel box-girder construction, supported on reinforced concrete foundations. It reportedly cost 3.5m euros to build. The designer was engineer GSE with architects Axel Schultes Architekten.

I think this is a decidedly odd bridge.

The bridge links two levels of the Chancellery across the river, and is itself a double-level structure. In cross-section, it is Z-shaped, with the two floors offset either side of the central span girder. This will have made it a tricky beast for the structural engineer to design, with an inbuilt tendency to twist under load, but it's nothing that can't be solved simply by throwing enough steel into the structure.

It seems like a pleasant arrangement, giving both levels the feel of a balcony. At the north end, the lower deck curves to pass below the upper deck. The spine beam element is aligned with a secure wall which protects the Kanzlerpark, so this arrangement allows both decks to pass on the inside of the boundary wall. Access onto the lower deck from adjacent riverside paths is prevented by tall glass screens.

The structural form is very curious. At first, I thought it was an interesting arch, with a feel somewhere between Bauhaus and art deco styles (it also, obviously echoes the simple geometrical shapes used in the Chancellory building itself). It can certainly be seen as a closed-spandrel arch, with the lower deck acting as a tension tie, suspended from the arch with a series of chunky "hangers". Alternatively, it's a bit like a Vierendeel truss. It gives the profound appearance of something not really thought through structurally: it is half wall and half bridge.

The main oddity for me, is the bridge's presence in the public realm. Perhaps German citizens feel otherwise, but I get the impression of something very much intended to display as publicly as possible a separation between citizen and government. Political masters can quite literally look down upon those they govern, and they are made visible but shown to be clearly off limits. The materialisation of a political relationship in this highly explicit manner seems to be something few democracies would consider, except perhaps France. It would surely have been simpler just to omit the north bank park and relocate the helipad elsewhere.

I think I'm not entirely alone in this sense of unease.

Further information: