Wrocław's Bridges: 16. Pipeline Bridge

This bridge is labelled "Gazociąg" by Wratislaveae Amici, which simply means "gas main" or "pipeline".

It was something of a surprise discovery - it isn't mentioned in any of the papers, guidebooks or websites that I looked at to work out what was worth seeing in Wrocław. I just glimpsed it in the distance and thought a closer look was merited, even though by this point myself and a companion were getting hot, tired and thirsty.

I guess its status as a utility bridge is responsible for its omission from guides to Wrocław's bridges, but that's a shame, as it's both a spectacular bridge, and also one of the most aesthetically pleasing that I saw.

I didn't have time to find a vantage point from which the whole bridge can be seen - it was simply too big. So you'll simply have to note that these photos show at most half of the bridge, and that the remainder is symmetrical (the Google maps link below makes it clear).

Spanning approximately 250m, this is a beautiful filigree suspension bridge. The cables are splayed, to provide the pipeline with a degree of lateral stability, and hence the pylons are also splayed, gigantic Y-shapes.

It would clearly be an absolute pleasure to walk across.

Further information:

• Google maps
• Wratislaveae Amici

Wrocław's Bridges: 15. Zwierzyniecka Footbridge

Heading eastwards and back out of town along the River Oder, you come to Kładka Zwierzyniecka.

Spanning 86m, this suspension footbridge's main function is to carry two large diameter water pipes across the river, although it was also well used by pedestrians when I visited.

It was built in the mid-1970s, and designed by M. Wróblewicz. The deck and towers are both in steel, and the bridge is self-anchored in form i.e. the main cable force is carried by the deck rather than anchored into the ground. The attachment between the deck and the cables can be seen on the right: triple cables are carried through a single pin into a stiffened cantilever bracket.

Zwierzyniecka Footbridge has a simple, highly functional design, to the point of near-brutalism. However, the lack of bright colour and odd protuberances makes me more sympathetic towards it than the other suspension footbridge I visited in Wrocław, the Frog Bridge.

It's not by any stretch of the imagination beautiful, but I quite like its sense of austerity.

The next post will be the final one in this series, and I've saved one of Wrocław's least known, but most impressive, bridges for last.

Further information:

• Google maps
• Wikipedia (Polish)
• Wratislaveae Amici
• Footbridges in Wrocław, Poland, Biliszczuk, Rabiega & Tadla, Footbridge 2008

Wrocław's Bridges: 14. Zwierzyniecki Bridge

The most striking feature of Most Zwierzyniecki is the overhead bracing which connects its twin truss arches.

The bridge was completed in 1897 (replacing a two span timber bridge) but according to Wiesław Jurewicz, it was modified in 1910 "due to the hazardous vibration of the arch girders". That may account for the presence of just so much overhead bracing, which functions both as X-bracing in plan, and portal bracing in cross-section.

The bridge was designed by Karl Klimm, A Fruhwirth, and Richard Plüddemann. It spans approximately 60m and is 12.5m wide between the truss centrelines, 21.8m wide in total. It carries a highway and tramway across a side channel of the River Oder, in the vicinity of Wrocław's Zoo and Centennial Hall. An earlier span was reportedly called the Paßbrücke because it formed a checkpoint at the city limites.

The main arch trusses have more than a hint of the later Hell Gate Bridge or Sydney Harbour Bridge about them. The upper chord is essentially a stiffening rather than primary load-bearing element, terminating in mid-air vertically above the lower-chord springing. This is disguised by the presence of decorative sandstone obelisks at each corner, just as the same effect is disguised by monumental abutments on the two larger and better know spans.

The yellow-gold colouring on the bridge's metalwork, and the intricacies of the truss and overhead bracing, put me in mind of a gilded cage, where the structure is as much as a shelter as a means of support for the floor.

You couldn't build a bridge quite like this today. Quite apart from the cost of the heavily laced metalwork, the hanger bars are unprotected against impact from traffic. While it's acceptable to design a bridge for the possibility of loss of a single hanger, this bridge clearly suffers from the potential for multiple hangers to be lost in a single incident.

Technicalities aside, I found Zwierzyniecki Bridge to be a lovely bridge, with a great deal of antique charm.

Further information:

• Google maps
• Structurae
• Wikipedia (Polish)
• Wikipedia (English)
• Wratislaveae Amici (includes pictures of the previous bridge at this site, and the current bridge under construction)
• The best known bridges in Wrocław
• Wrocław Mosty - Bridges - Brücke, Wiesław Jurewicz (undated book, ISBN 978-83-926759-5-2)

Wrocław's Bridges: 13. Frog Footbridge

The Kładka Bielarska (or Kładka Żabia) connects Bielarska Island to the main river bank. There has been a suspension footbridge here since 1975, although it was largely reconstructed in 2002, including extensive reinforcement of the foundations with micro-piles. Before that, a truss bridge occupied the site. The bridge was designed by Kazimierz Gałajda, with the reconstruction attributed to Joseph Rabiega.

The bridge spans 56.5m, with pylons 10.5m high. The main suspension cables are 46mm spiral strand ropes. Both the pylons and the main deck beams are made from 457mm diameter steel tubes.

The pylons consist of portal frames, with the crossbar and legs each comprising twin tubes, "stitched" together with cross-stiffeners. These are ungainly enough, but made worse by the addition of frog-like protrusions at the top which carry lighting units. Presumably these give the bridge its "Frog Bridge" nickname.

Sadly, the paired tubes are not unique to this bridge - I've seen them on a photo of another Polish footbridge. Overall, the styleless reliance on tubular steel in combination with bold colouring is emblematic of an undesirable trend which seems to have informed a great deal of Polish footbridge design.

The bridge evidently suffered from considerable vibration prior to its reconstruction, and tuned mass dampers were added to the midspan and quarter span points. These are large dampers, and quite easily visible in the first photo of the bridge above.

Further information:

• Google maps
• Structurae
• Wikipedia (Polish)
• Wratislaveae Amici
• Footbridges in Wroclaw, Poland, Biliszczuk, Radiega & Tadla, Footbridge 2008
• Redukcja drgan kladek dla pieszych z wykorzystaniem tlumikow masowych, Dalmer, Fiebig & Rabiega, 2004 (Polish, explains the addition of the tuned mass dampers to the bridge)

Wrocław's Bridges: 12. Malt Footbridge

Not far from Kładka Piaskowa, another footbridge can be found which was built at the same time (2003), linking Słodowa island to the main riverbank. Kładka Słodowa is a steel bowstring arch bridge, with inclined hangers forming a triangulated system (this is stiffer than using vertical hangers, but is prone to load-reversal in the hangers if they are not sufficiently pre-tensioned). The designers were Research & Design Office Mosty-Wrocław with ISBA architects.

The arch spans 48m, and is 15.6m tall. It consists of two tubes, 508mm in diameter, and parabolic in profile, intersecting at a high level. Some form of connection is essential to brace the arches against buckling, but the choice to intersect in this way is essentially an arbitrary one.

The bridge deck consists of a cellular steel box girder with a curved soffit plate, similar to the nearby Sand Footbridge, and which picks up reflected light from the river in a similar manner. The deck is paved in blue-grey sandstone slabs.

The bridge elements were fabricated in a shipyard and brought to site by boat for final assembly. The arch was assembled lying on its side, with a temporary bowstring for support, before being lifted by crane into the vertical position. Three deck sections were then erected one by one using temporary vertical strands for support.

This is a reasonably straightforward and attractive design. The view of the cables gets a bit confused because of the variation in angles seen from anywhere other than side-on to the bridge. As with the Sand Footbridge, the olive-lemon green colour is not unattractive, especially amongst trees, and the deck looks slender.

I'm not sure why they went for a different parapet here - mesh infill panels rather than horizontal wires - and as at its sister bridge, the parapets look quite utilitarian.

It's interesting to see one of the alternative options that was considered for the site, an asymmetric cable-stay bridge without any back-stays supporting the pylon (shown below). This would clearly have been more expensive, both in terms of the superstructure and the foundations.

Further information:

• Google maps
• Structurae
• Wikipedia (Polish)
• Wratislaveae Amici
• Examples of newly built footbridges in Poland, Biliszczuk, Berger, Machelski, Wegrzyniak, Onysyk & Prabucki, Footbridge 2002
• Footbridges on the River Odra's Islands in Wroclaw, Styrylska, Boniecki, Biliszczuk, Barcik, Rudze & Stempin, Footbridge 2005
• Footbridges in Wroclaw, Poland, Biliszczuk, Radiega & Tadla, Footbridge 2008

Wrocław's Bridges: 11. Sand Footbridge

Most of the bridges in Wrocław that I've covered so far in this series have been historic in nature. The next two or three, however, are all relatively contemporary designs.

Kładka Piaskowa was built in 2003, and is a three-span pedestrian bridge (spans 4.5m, 45m, 4.5m), designed by Research & Design Office Mosty-Wrocław with ISBA architects. The deck is 3.19m wide and 1.06m deep, and comprises a steel box girder with a curved soffit. The deck is painted a lemon-olive colour, while the steel parapet post are painted light grey. The deck surfacing consists of Iroko hardwood planks.

Essentially, it operates as a fixed-ended beam, which allows the relatively large span-to-depth ratio to succeed. The deck is of a constant depth, but is lightly arched. The photo on the left illustrates the support system. The transition to the much shallower approach ramps looks as good as can be expected for something which is always very awkward.

The bridge was erected by "pull-launching", with its front end supported on a barge while the whole deck was towed across the river from one bank.

What's especially pleasing about this footbridge is its undemonstrative nature - there is no attempt to be unnecessarily showy, unlike some Polish footbridges. The low profile was a deliberate attempt not to interfere with historic riverbank views. The parapets are somewhat utilitarian, but not so much as to ruin the design.

The curved underside of the deck picks up shimmering reflections from the water below, and enhances the impression of slenderness. The colour seems initially a little odd, but it is muted rather than garish.

Further information:

• Google maps
• Structurae
• Wikipedia (Polish)
• Wratislaveae Amici
• Footbridges on the River Odra's Islands in Wrocław, Styrylska, Boniecki, Biliszczuk, Barcik, Rudze & Stempin, Footbridge 2005
• Footbridges in Wrocław, Poland, Biliszczuk, Radiega & Tadla, Footbridge 2008

Wrocław's Bridges: 10. Saint Clare Bridge

What's that? You think I have included Most Świętej Klary in this series solely so I can feature a photo of a nun on a bridge? Ok, I confess.

This appears to be a two-span timber truss bridge, although there are steel members visible below as well.

Further information:

• Google maps
• Wikipedia (Polish)
• Wratislaveae Amici

Wrocław's Bridges: 9. Słodowa Bridge

I'm including Most Słodowy simply for completeness, and because it is the only road crossing onto the Słodowa island.

There are a series of islands at this point in Wrocław, within the boundaries of the River Oder, and for most of the town's history, access to them has been limited. The construction of two footbridges (both of which I'll come to soon) in recent years has greatly improved accessibility.

The present structure is a temporary Bailey bridge, with a separate pedestrian walkway to one side. It spans only about 8m. From what I can determine, this must be relatively recent, as most of the information on the internet and linked below refers to a steel beam structure which is clearly no longer there.

Further information:

• Google maps
• Wikipedia (Polish)
• Wratislaveae Amici

Wrocław's Bridges: 8. Mill Bridges

The two Mosty Młyńskie originally spanned over the streams for two watermills, named Maria and Feliks. The latter mill has been demolished, but the former is still present, although disused.

As with Sand Bridge, there were bridges here for several centuries. The current steel parabolic arch trusses date from 1885, and are clearly a more developed design than the Sand Bridge. The general form of the truss is such as to follow the typical bending moment diagram for a simply-supported span, making a more efficient use of material than in a more uniform truss. The web members are also more open than in the lattice truss form which was previously prevalent.

The two bridges span 28m and 36m respectively, and are of slightly different heights. The slightly flattened top to the trusses is characteristic of the so-called Schwedler Truss. I presume it was done this way to cater for the variability in live load positioning, responding to the envelope of load effects rather than simply uniform loading over the entire span.

The northern of the two spans is currently being refurbished, and the bridge is closed to its normal roadway and tramway traffic.

In their current form, I am not greatly enamoured of the bridges. They are very honest structures, but as Schwedler himself is reported to have believed, the flattened arch form is not the most attractive.

Further information:

• Google maps
• Structurae
• Wikipedia (Polish)
• The best known bridges in Wrocław
• Wratislaveae Amici (includes historic photos of the bridges and their timber predecessor, and images taken during the present and previous refurbishments)
• Wrocław Mosty - Bridges - Brücke, Wiesław Jurewicz (undated book, ISBN 978-83-926759-5-2)

Wrocław's Bridges: 6. Tumski Bridge

Most Tumski is a bridge over a branch of the River Oder. There has been a bridge here for centuries, marking the boundary between the jurisdiction of the city authorities on one side, and the cathedral authorities on the other.

The current steel truss bridge was built in 1889. It originally carried road traffic, but is now pedestrianised. It was damaged in the second World War, but repaired, and has been extensively refurbished in more recent times. It is illuminated by antique gas lanterns at night.

The bridge's two spans total 52m in length. There is a small skew, although this is not really noticeable. The structural form is clearly unusual. It's essentially a truss structure, although with some of the attributes of a suspension bridge, notably the separation of the top chord from the stiffening truss, where it passes above the central pier.

The main verticals of each truss form the sides of a portal gateway, providing much of the bridge's sense of occasion. The portal presumably also serves to stabilise the verticals against lateral buckling.

It's quite remarkable that what is normally seen as heavy and industrial, the riveted steel truss, can not only fit within a historic environment so well, but also become such a romantic bridge.

I'm not sure why it became associated with romance, but the bridge is now home to a tradition where couples come to seal their relationship vows. They prepare a padlock to symbolise their commitment, often inscribed with their names or a suitable message, lock it to the side of the bridge, and then throw the key into the river, indicating the unbreakable nature of their commitment (I'm not sure whether Wrocław divorce lawyers have to employ assistants armed with boltcutters).

The bridge is now lined with hundreds of locks, and it's a tradition I believe has spread to other bridges elsewhere in Poland. Tumski Bridge is surely one of the best-known bridges in Wrocław, and possibly my favourite out of those I visited.

Further information:

• Google maps
• Structurae
• Wikipedia (English)
• Wikipedia (Polish)
• The best known bridges in Wrocław
• Wrocław Mosty - Bridges - Brücke, Wiesław Jurewicz (undated book, ISBN 978-83-926759-5-2)
• Wratislaveae Amici (includes historic photos and drawings, some showing the predecessor bridge, and the present bridge under construction)

Wrocław's Bridges: 5. Hospital of St Joseph Bridge

I have even less to say about this bridge than the last one. It spans between the Hospital of St Joseph (on the left), and the Assembly of St Elizabeth (on the right).

Further information:

• Google maps

Wrocław's Bridges: 4. Museum Footbridge

Continuing west along the River Oder, the next bridge, Kładka Muzealna, forms part of the southern river bank, spanning over a small inlet where boats are moored, called Gondola Bay (Zatoka Gondoli).

The previous wooden footbridge here was replaced in 1928 with the present reinforced concrete arch. The bridge deck is 30m long, but the arch spans only 20.5m.

I walked along the opposite river bank, and didn't get the chance to see this bridge up close.

Further information:

• Google maps / Bing maps
• Structurae
• Wratislaweae Amici (several historic photos of the present bridge and its predecessor)
• Wikipedia (Polish)

Wrocław's Bridges: 3. Peace Bridge

Most Pokoju is the next crossing of the River Oder in Wrocław as you head west from Most Grunwaldzki. The River is crossed several times within the city centre, but Most Grunwaldzki is the last highway crossing to the east for quite some considerable distance.

 A timber bridge originally spanned the Oder at this point, replaced in 1875 by the steel Lessing Bridge. This was damaged so badly in 1945 that it had to be replaced, although the new bridge was not completed until 1959. It took its present name, the Peace Bridge, in 1966. The designer was Jan Kmita.

The bridge is a hollow reinforced concrete box structure, with a central drop-in span supported on half-joints from the side cantilevers. It's what is known as a "Gerber beam", after the German engineer, Heinrich Gerber, who patented this system in 1866. Hinges are introduced at what would be the points of contraflexure in a continuous beam. This reduces the overall bending moments required for design (compared to a simply-supported system), while eliminating stresses which might result from thermal restraint or differential settlement. It also makes the structure easier to analyse, which was perhaps the major advantage when the idea was first introduced.

Of course, the major disadvantage is that the half-joints are prone to deterioration (e.g. from de-icing salts) while simultaneously being difficult or impossible to inspect and maintain properly: the Laval Overpass collapse being a relevant case history.

It's certainly not an unattractive bridge, with a relatively slender outline and simple, straightforward lines. The only element which strikes me as odd is the use of little mini-corbels to support the deck cantilever above the pier positions, which I can't quite see the point of, even considering that this is where the lighting columns sit.

Further information:

• Google maps / Bing maps
• Wikipedia (English)
• Wikipedia (Polish)
• Structurae
• The best known bridges in Wrocław
• Wrocław Mosty - Bridges - Brücke, Wiesław Jurewicz (undated book, ISBN 978-83-926759-5-2)
• Wratislaweae Amici (includes several historic photos and images including the predecessor bridges)

Wrocław's Bridges: 2. Grunwaldzki Bridge

Most Grunwaldzki is one of the most unusual suspension bridges I have ever seen.

It results from a 1905 design competition won by the engineers Robert Weyrauch, Martin Mayer and Alfred von Scholz, and carries pedestrians, vehicles and trams across the River Oder. The architectural design was attributed to Richard Plüddemann. At the time, Wrocław was part of Germany, and called Breslau. The bridge was originally named the Kaiserbrücke, in honour of the last German Emperor, Wilhelm II, who opened the bridge in October 1910.

The bridge was severely damaged in the second World War, but rebuilt by 1947. In the process, the appearance was slightly altered, with turrets being removed from the towers, giving them a more modern appearance.

The bridge's arch-portal towers are built in granite, while the 112.5m span is in the form of steel Warren trusses (the horizontal member running in front of the trusses is a support for an underslung maintenance gantry).

What makes the bridge unusual is the suspension "cable", which isn't a cable at all, but a set of riveted steel plates. I'm not aware of any other suspension bridge quite like it. Both the Salzach Bridge in Laufen, and the Tower Bridge in London, have suspension "cables" made from riveted steel, but not in this flat-plate form. Each "cable" consists of four bands, each with up to eight layers of plate. Even the hangers are in riveted plate.

The use of riveted plates for the main suspension system is of course incredibly inefficient, as mild steel plate has a tensile strength several times lower than that of drawn steel wire. The use of wire cables in suspension bridges dates back to the 1820s, and was widespread by the time of the Kaiserbrücke, making the decision all the more puzzling. A few suspension bridges using metal chains were still being built into the twentieth century, such as the 290m Elisabeth Bridge, erected in Budapest in 1905, and the very late 340m Florianopolis Bridge, erected in Brazil in 1926. Nonetheless, the Grunwaldzki Bridge is probably unique. In addition to the low strength of its suspension "cables", it must have been much harder to build than a wire-cable bridge, as the riveted plates will have required temporary support until complete.

The anchorages are also an unusual feature. In most suspension bridges, the cables are continued at an angle into the concrete foundations or underlying bedrock. On the Grunwaldzki Bridge, they are turned about a stiffened, hinged saddle, such that they enter the ground vertically. This isn't unique - Navier's Pont des Invalides also had a vertical cable anchorage (see page 6 of the link for an image). I guess this offers the advantage that where the anchorage foundation may be prone to lateral movement, it can be buttressed in compression rather than relying on a tension ground anchorage. A diagram available online shows that the anchorage chamber is strutted against the tower foundations for stability.

Despite the clunkiness of the engineering, this is an attractive bridge. It is monumental, with a robust impression of strength. At the same time, the blue paintwork lightens the appearance. It is well-detailed: even the lighting columns are in riveted steel in similar style to the rest of the bridge. The towers are massive but not ridiculously so.

It's one of the best known bridges in Wrocław, and rightly so, and with its unusual engineering has a historical significance which is much wider.

Further information:

• Google maps / Bing maps
• Wikipedia
• Structurae
• Most Grunwaldzki [PDF, Polish]
• The best known bridges in Wrocław
• Enjoy Wrocław - Local Tips for Tourists
• Wrocław Mosty - Bridges - Brücke, Wiesław Jurewicz (undated book, ISBN 978-83-926759-5-2)
• We'll Gather at the River, Christian A. Dumais
• Wratislaweae Amici (includes several historic photos, drawings, and images of the bridge under construction)

Wrocław's Bridges: 1. Introduction

Wrocław is sometimes described as the Venice of Poland: a city built on 12 islands connected by 112 bridges (although other sources suggest there are at least 220 bridges and I'm sure the latter figure is closer to the truth). The land areas are divided by both rivers and canals, and in places by the town's old moat.

While in Wrocław for Footbridge 2011, I had the chance to visit a handful of those 112 or 220 bridges, which I'll cover in the next few posts.

Of the more significant bridges in Wrocław, I'm most disappointed at not having had time to visit the recent timber footbridge over the old moat (pictured). Its design was discussed in the paper Conceptual design of a footbridge in the historical part of Wrocław at Footbridge 2008, and it's nice to see such a muted, self-effacing design, as so many new footbridges in Poland are unnecessarily dramatic and brightly-coloured.

Further information:

• Examples of newly built footbridges in Poland, Biliszczuk, Berger, Machelski, Wegrzyniak, Onysyk & Prabucki, Footbridge 2002
• Footbridges on the River Odra's Islands in Wroclaw, Styrylska, Boniecki, Biliszczuk, Barcik, Rudze & Stempin, Footbridge 2005
• Footbridges in Wroclaw, Poland, Biliszczuk, Radiega & Tadla, Footbridge 2008
• The best known bridges in Wroclaw
• Detailed guide to bridges of Wroclaw [PDF] (Polish)
• Bridges and crossings in Wroclaw (Wikipedia, Polish)
• Wrocław Mosty - Bridges - Brücke, Wiesław Jurewicz (undated book, ISBN 978-83-926759-5-2)