The Happy Pontist

Bridges news roundup

2012-01-25T22:05:00.001Z

Regular readers will have noted I am not posting much right now - this is likely to continue for the indefinite future as I am busy with other things. Sorry!

Ten Remarkable U.S. Bridges
Some great bridges, especially Bardwell’s Ferry Bridge.

Work begins on new Salford footbridge
The third of five new bridges apparently, I believe this is a Ramboll WhitbyBird design.

Criticism of bridge design hasn’t let up
Columbia River Crossing is the scene of a fierce battle between appointed experts and self-appointed experts.

'Kissing bridges' of Northumberland County?
Ontario politician ponders whether ersatz covered bridges could attract tourists. Surely brand new covered bridges will lack the appeal of historic spans?

A bridge to the future of scouting
"Wing Tip Bridge" due to open in 2013, looks like a very interesting design.

Think the school run is bad?
I wouldn't normally link to the Daily Mail, but the pictures and video are pretty remarkable.

Polhollick Suspension Bridge to be upgraded
£350,000 required to refurbish Listed bridge in Deeside, Scotland.

Peter's Bridge, Norwich

2012-01-15T18:15:00.000Z

I always prefer to visit a bridge before covering it here, but I have no plans to go anywhere near Norwich soon, and this bridge looked worth featuring.

It opened to the public last month, and spans the River Wensum in Norwich city centre. Spanning about 30m, it is 80m long in total, shaped like the letter "J" in plan. Designed by Ramboll, it is named for Peter Jarrold, who first came up with the idea for a bridge at this site twenty years ago.

The bridge's form is unusual - there are plenty of bridges with curved decks like this, but very few with so little obvious means of support. Most are suspended from arches, or masts, or less frequently held up by larger girders or trusses.

Peter's Bridge is built primarily in weathering steel, with a torsionally stiff box girder on the inner edge of the curve, supporting braced steel ribs. The deck has a wedge-shaped cross-section, emphasising the outer edge and making it look thinner than it really is. The deck cross-section of York Millennium Bridge has several similarities. The photos are unclear, but there appear to be a small number of very slender supports below the main edge girder.

The parapets are a combination of weathering steel uprights with stainless steel handrails and, on the outer face, mesh infill. It's a combination of materials that can be very attractive, as I've illustrated here before. However, it's also prone to vandalism and to the risk of rapid corrosion due to trapped water, particularly in the British climate.

Here, timber panels are used to prevent direct contact with the rusty inner face of the support girder, although I would not be surprised to see graffiti on the outer face of the girder in the future - this is difficult to clean off without creating a patchy finish. The deck is also timber-planking, with gaps allowing rainwater to drain straight through, and it will be interesting to see how well that performs or whether trapped moisture affects the support ribs over time.

Quibbles aside, the overall appearance is daring without unnecessary flamboyance, and it looks like a fine new structure, nicely detailed.

All photos are courtesy of mira66 on flickr. You can also see online images of the bridge under construction.

Bridges news roundup

2012-01-12T12:58:00.001Z

Ornithological Observatory / Manuel Fonseca Gallego
Not a bridge, but certainly bridge-ish (image © Luís Prieto Sáenz de Tejada).

Will 2012 Deliver Promised New Frontiers? The Margaret Hunt Hill Bridge
What will Calatrava's new bridge mean for Dallas? "Will its legacy mark a shift in civic thinking, leading to new models of development and forward-thinking urban practice? Or will it serve as yet another symbol of Dallas’ bloated ego, its propensity to invest in the loud and the most expensive as part of the perpetual pageantry of gregarious societal theatrics?"

For even greater bile and hyperbole, on the occasion of the switch-on of the bridge's lighting, see this Dallas Observer blog.

Unbuilt London: Bridges To Nowhere And Mad Masterplans
Short survey by the Londonist blog. For much more on the theme of bridges that never were, in London, see also my previous posts: Millennium Bridge, Thames Water Habitable Bridge, Leamouth, Royal Victoria Dock, Carpenters Lock, and Peabody Trust Habitable Bridge.

World's tallest bridge hailed in Mexico
The virus that the Baluarte Bridge is the "world's tallest bridge" seems to have spread widely across the web, and the good old BBC were one of many news organisations who played their part in spreading it. Even New Civil Engineer, who should know better, perpetuated the meme before correcting their story a few days later.

The Guinness Book of World Records gets it right however: it's the world's highest cable-stayed bridge (and, according to highestbridges.com, the third highest bridge overall). The Millau Viaduct is the tallest, as one minute on Google would have told lazy journos.

Why was this bridge allowed to decay?
If the author is to believed, a rare example of a surviving James Dredge suspension bridge (Victoria Bridge, in Bath) has deteriorated severely, largely due to an incorrect assumption that developer funding would save the local council from having to look after it properly. The slightly more measured account from the council suggests work is in hand to prop and eventually refurbish the bridge, to reopen it in 2013.

Design chosen for St Botolph's footbridge, Boston

2012-01-11T21:05:00.000Z

As I said last time I mentioned this story, that's Boston, Lincolnshire, not Boston, Massachusetts.Lincolnshire County Council and Boston Borough Council have chosen a "bowstring arch" as their preferred design for a new footbridge in Boston town centre.

Out of a town population of 55,750 or so, a massive 60 people voted for this design in a public consultation, against 77 people preferring an alternative. The new 35m span bridge will have twin tubular arches.

A planning application is expected later this year, with construction expected to start in mid-2013.

"River Axe Crossings: from Mouth to Source"

2012-01-05T21:38:00.000Z

I strongly suspect 2012 is going to be a fairly quiet year here at The Happy Pontist. The myriad obstructions which clutter "real life" have obliged a fever of activity, both necessary and unnecessary, which will leave limited time for my more idle whims such as blogging.

With this in mind, it's perhaps appropriate that my first post of the year is to feature a book, Colin Sackett's "River Axe Crossings: from Mouth to Source" (2008, www.colinsackett.co.uk), in which bridges are essentially conspicuous by their absence.

Opening the book from what is normally seen as the "front", it is titled "Upstream: River Axe Crossings from Mouth to Source". Each right-hand page then offers a picture of the River Axe looking upstream, photographed from each of forty-one consecutive river crossings (weirs, fords and rail bridges are excepted, not unreasonably). This takes the reader on a journey through Devon, Somerset and Dorset, all predominantly rural counties in England's south west.

Opening from the "back", the book's title is "Downstream: River Axe Crossings from Source to Mouth", and every left-hand page depicts ... oh, you probably guessed already. The photographs taken at the river crossings are bookended by images from the river's source and mouth.

Every photograph is in black-and-white, and accompanied by a brief paragraph with details on the crossing in question, or on what can be seen in the distance. The change in appearance of the river and its banks from a tightly constrained woodland watercourse, through open fields, back through woodlands, and eventually into a wide, open floodplain is quietly interesting, and a remarkably informative way to consider the details of a highly particular landscape. You can find some example images from the book at the author's website.

Although the book is clearly a one-off, it's easy to imagine a series of similar volumes depicting other rivers, or imposing order on entirely different features of the landscape. I'm reminded of the artist Richard Long, and his landscape journeys planned according to imposition of an artificial geometry onto a survey map (one example). There is a similar sense of using an entirely arbitrary system to order a journey and hence disrupt the way we normally encounter the landscape.

Many of the photographs make clear how this particular river, flowing as it does through a floodplain of varying width, both determines how people have altered the landscape, and is affected by human actions. The nature of the river banks, often in deep cut, reflects the use of the river as a boundary, as well as its diversion past other boundaries. It also makes clear the predominantly agricultural nature of the area, cleared of vegetation which might restrict the river's ability to erode and meander.

Bridges do appear occasionally, in the distance, where they can be seen from another crossing, or by implication, whenever an image has clearly been taken from the perspective of a taller span. Although they define the entire structure of the book, they are invisible platforms, present only because they allow the photographer to stand on the centreline of the channel without getting his tripod wet. Nonetheless, you can tell a little about their nature by considering the gaps between the photographs - stretches of the river which don't merit a crossing, or where one is uneconomic.

As a pontist who normally photographs bridges as an object in their own right (the structural engineer's focus) or as an object within a landscape (a nod to architectural friends), the absence of bridges from this book of river crossings comes as something of a shock, but a welcome one. It's too easy for an engineer to forget that bridges are not only there to cross, but to stand upon, that they establish a relationship not just between the two river banks but also allow their user a very different perspective upon their surroundings.

Post-structuralists in literature have long been au fait with the possibility for the author to disappear from the text. Perhaps it is time for post-structural pontists to likewise celebrate the disappearance of bridges from the landscape.

Bridges news roundup

2011-12-21T21:19:00.000Z

Moxon completes Taunton bridge
Modesty is a virtue (pictured - more images at Moxon's website).

Polyurethane/steel deck wins Canadian design award
Sandwich plate deck system used to minimise dead load in bridge refurbishment scheme.

Memorial Bridge Design Battle Just Beginning
Busybody seeks to add pointless frippery to New Hampshire bridge design.

New River Wear bridge in Sunderland given the go ahead
Government accepts arguments that "iconic" element of controversial design offers good value-for-money, finally securing the future for the new Wear bridge. This is something of a triumph for designers Stephen Spence and Techniker, who saw their initial design contest entry disappear into a black hole before it was eventually revived. Considerable effort has gone into making this bizarre design stand up, and I hope more details of the engineering become available in due course, through a technical paper perhaps.

Sturgess: An unusual process yields an extraordinary result: Peace Bridge
A quite extraordinary love letter to Calatrava's still incomplete Calgary footbridge.

Wow! That's one nice-looking bridge
The Calgary Herald calls it "iconic but overpriced". Get off the fence - was it worth it? A late January opening is currently anticipated.

Be’er Sheva Pedestrian Footbridge
Winning proposal for yet another "iconic" project (pictured). Slightly reminiscent of the Gatwick Pier 6 passenger bridge.

Gateshead Millennium Bridge bollards to go
Hurray!

City of Toronto halts new Lovelocks fad on Humber River foot bridge
Joy-killing jobsworths hard at work in Toronto.

London Bridges: 21. PaddingtonCentral Footbridge

2011-12-20T00:02:00.000Z

This is the last of four footbridges that I visited in Paddington Basin, London. It is the furthest west of the group.

I will confess that what first attracted me to go and visit this bridge was a photo of it online showing the slightly unfortunate positioning of one of the main support legs - right in the middle of the access ramp! It has clearly been built on a very constrained site, but I'm at a loss as to why they couldn't avoid this.

The bridge design seems to pick up on several common features of a "modern" pedestrian bridge, throwing them together in a haphazard jumble that not only is unnecessary at this site, but would be so at any site. These design features aren't connected by the usual logic.

One feature is the use of cables to support the bridge on one edge. The pylon is connected to the deck with a series of cables, and is anchored by back-stays to the ground. At this sort of span, cable support isn't really necessary, and when you see the bridge from underneath, it appears doubly so.

The bridge is supported on Y-shaped steel frames at each end of the main span, and the main girder looks beefy enough to hold the entire deck up on its own. The cables introduce a horizontal force into the deck which must be resisted by the Y-shaped frames, emphasising the artificiality of the layout (the horizontal force is normally carried as a thrust in the deck directly back to ground). With this arrangement, supporting via vertical hangers from an arch would have made more structural sense.

The circular edge girder is positioned in such a way that there's no clear continuity between the access ramps and the main span's bridge deck. No doubt some of this ungainliness is a result of the constrained site, but I suspect more of it comes from trying to match the bridge's necessary geometry to an arbitrary and inappropriate choice of structural form.

In short, it's an object lesson in how not to design a footbridge, well worth visiting just to see what mistakes to avoid.

Further information:

Google maps / Bing maps
Discover Paddington Waterside (walking tour)
CMF (steelwork fabricator)

London Bridges: 20. Station Footbridge, Paddington

2011-12-13T21:14:00.000Z

Proceeding west from the Rolling Bridge, I'll skip past a very dreary cable-stayed footbridge and move on to one that is a little more interesting.

Designed by Langlands and Bell with Atelier One, the main section of this footbridge is 44m long, with a 19.6m main span. The deck is 3.5m wide, and is suspended below a glass-clad steel "sail", 8.4m high. Langlands and Bell are artists (I think this may be their only bridge design?), not architects, specialising in an quixotic blend of styles which I would think of as pop-art-meets-minimalism. At Paddington, minimalism wins out - this is a bridge as if designed by Donald Judd.

The effect is quite unlike most footbridges. It's a proper gateway structure, proffering a letter-box entry to Paddington Basin from the west, and helping to hide an unattractive building when approached from the east.

Structurally, it is not especially complex. The walkway is a simple grillage of steel beams, suspended at midspan by a single hanger, with diagonals partially obscured by the glazed enclosure above. The form is an inverted king post truss, which is about as simple as it gets. The walkway cantilevers to either side of the support structure, supporting structural glass balustrades.

I think the glazed wall is visually very effective, particulary in images showing it illuminated at night. It's non-functional, in the sense meaningful to an engineer - it makes the structure harder to design, by adding enormously to the wind load, but the central cut-out prevents it from acting as a wind-screen. It allows for multiple alternate crossing experiences, and is boldly assertive but visually permeable.

Even visiting it on a dully grey day didn't harm it much. It helps distract from the dreary nature of the nearby building, and even from an adjacent construction site.

I like it.

Further information:

Google maps / Bing maps
Discover Paddington Waterside (walking tour)

London Bridges: 19. Rolling Bridge, Paddington

2011-12-11T17:20:00.000Z

Heading west from the Helix Bridge, the next footbridge at Paddington Basin is the Rolling Bridge, easily the best known of the set, and justifiably so.

I would guess few of my readers will be unfamiliar with this bridge, as it is one of the most remarkable and audacious footbridge designs from the last decade. As with the Helix Bridge, it's something of a white elephant, spanning a very small side-arm of the canal, which goes nowhere and has no real reason for continued use by boats. The bridge is useful in providing a direct route along the edge of the main canal basin, but it doesn't really need to open.

Nonetheless, it does open, every Friday at noon. Sadly, I was there on a different day of the week. The opening mechanism is unique: the bridge slowly curls up from its level position, ending up in the form of an octagon when fully open. Its initial form, which broadly resembles a modified Warren truss, is distorted by extending eight hydraulic cylinders in each of the trusses.

Most moving bridges operate on the principles of translation (lifting and retractable bridges) or rotation (bascule and swing bridges). Very few adopt the principle of transformation, indeed about the only other examples which come to mind are Schlaich Bergermann's folding bridge at Kiel and arching bridge at Duisburg.

There is a sense that the Rolling Bridge's design is just a gimmick, but on balance I think not. It's delightfully inventive, playfully so, with the resemblance to a curling caterpillar responsible for a significant cuteness factor.

It was designed by Thomas Heatherwick, with structural engineering by Packman Lucas and SKM Anthony Hunt. The steelwork was fabricated by Littlehampton Welding. It cost £330,000 in 2004, which seems a lot for a 12m long bridge, but was surely worth it.

Up close, the detailing is nicely done, although the bumpy profile of the top rail in the at-rest position looks a little odd. It's often a problem with "iconic" opening bridges that their sense of spectacle is lost when they are closed. With the Rolling Bridge, it still retains a sense of potential, like a muscle tensed and ready to flex.

Further information:

Google maps / Bing maps
Structurae
Wikipedia
movablebridges.org.uk
Discover Paddington Waterside (walking tour)
Footbridges (Baus and Schlaich, 2008)
An Encyclopaedia of Britain's Bridges (McFetrich, 2010)

London Bridges: 18. Helix Bridge, Paddington

2011-12-06T23:19:00.000Z

The next few posts follow something of a guerilla tour around the footbridges of Paddington Basin, London. This canal terminus has undergone considerable redevelopment over the last decade, and a number of bridges have been installed both to improve access and to gain attention through their novelty value.

Before visiting, I'd heard of a fellow bridge photographer who had been unable to take pictures on the site thanks to over-zealous security guards. I'm a pontist, not a terrorist, but I thought it best to take photos quickly and not hang around. You'll therefore have to bear with me if some of the photos aren't of the best quality.

Somewhat prosaically also known as the "East Bridge", the tiny Helix Bridge provides access across the east end of the canal basin at Paddington. Completed in 2003, it spans a mere 7.2m. It was designed by Buro Happold with artist Marcus Taylor, and built by Davy Markham.

It is designed to retract, giving the impression of a corkscrew as it does so, albeit very, very slowly, moving at a snail-like 75mm per second. The "corkscrew" effect is simulated: the enclosure assembly rotates on bearings within the two circular end hoops. These in turn are supported from a retractable 2m wide walkway structure, which cantilevers from one end. This sits on a powered trolley, which runs on rails. As the walkway retracts, the enclosure rotates.

The 3.5m diameter enclosure comprises 15mm thick curved glass panels, glued to the tubular framing. The main spiral element is a 140mm diameter stainless steel tube. The bridge has clearly been altered since construction, with what were previously transparent panels now replaced or covered in blue material. I presume this is a response to vandal-related glass breakages.

I gather that the bridge has not been able to operate for some time, and have seen a comment from British Waterways on an online canal forum that it would "cost a considerable sum of money to repair", clearly disproportionate to the value that opening provides. BW also report that the bridge is due to be replaced by a new lifting bridge, presumably one with a less complex mechanism, and hopefully not destined for a similarly early graveyard.

Further information:

Google maps / Bing maps
Structurae
movablebridges.org.uk
LUSAS
Discover Paddington Waterside (walking tour)
An Encyclopaedia of Britain's Bridges (McFetrich, 2010)

London Bridges: 17. Challenge of Materials Footbridge

2011-12-04T21:36:00.001Z

I spotted these photos from earlier this year lurking in my files, and realised it was a bridge I hadn't yet featured here. These aren't great photos, I was in a hurry and didn't have time to find a good viewpoint.

The bridge was designed by Whitbybird and Wilkinson Eyre and spans the main hall in London's Science Museum, providing access to the Challenge of Materials gallery.

The bridge is intended to use the bare minimum of materials, with 16m spanned by 8.5 tonnes of glass and steel. The deck comprises 828 glass plates placed on edge, the ideal arrangement to resist the compressive stresses introduced by the cable-stay support arrangement. The balustrades are in the form of glass plates.

The "stays" are a closely spaced fan of stainless steel wires, each a mere 1.58mm thick. Each wire runs from a support fan bolted to the building's columns, down to the deck, across the underside, and then back to another support fan. Tie-down cables below the deck ensure rigidity and prevent vibrations.

From several angles, as will be apparent from the photographs, the ultra-slender wires almost become invisible, leaving only an evanescent presence in the air. From other perspectives, the light glints off the wires, and elements of their cat's cradle geometry are revealed. This is my favourite aspect of the design: the supporting wires define a wider space for the walkway to rest within, but the effect is subtle rather than intrusive.

The glass floor and sides, which you might expect to give a sense of precariousness, are surprisingly unexciting: the sheer rigidity of the structure eliminates any sense of peril.

Further information:

Structurae
Wilkinson Eyre: Bridging Art and Science (2001)
Bridge Builders (Pearce & Jobson, 2002)
Footbridges (Baus & Schlaich, 2008)

Bridges news roundup

2011-12-02T12:54:00.001Z

It's time for another very quick roundup of bridge-related news.

Hopefully in the near future I'll get some more spare time, and I plan to post about a series of footbridges in the Paddington area of London which I visited recently.

Walk of Faith: Glass Pavement for Tourists Built on 4,690ft Mountain in China
That's another place added to my future holidays list.

Shrewsbury footbridge to undergo major refurbishment
£450,000 to refurbish a bridge which originally cost £2,600. It would certainly be a shame not to preserve this fine bridge, but you could probably build an entirely new bridge for that sum.

9 Beautiful Pedestrian Bridges Not Designed by Santiago Calatrava
The design credits generally omit the engineer, and several of these actually look rather horrible, but it's nice to see lesser known structures getting some recognition.

Peace Bridge placed over Bow River
The long-running saga of Calatrava's Calgary bridge seems to be approaching an end. Some people still find time to grumble.

Bridges news roundup

2011-11-22T21:15:00.001Z

Life is busy, busy, busy, so you will have to make do with a quick roundup of mostly out-of-date news for now ...

Money Secured for 3 Dallas 'Signature' Bridges
Pockets emptied for Calatrava designs.

Race starts for £118m Wear bridge before approval
Sunderland City Council goes to tender on unfunded iconic bridge.

Peace Bridge will be red, inside and out
As delayed Peace Bridge hits one-year milestone, questions surround cost overrun
Costcutting continues but Calgary bridge still not ready.

Invisible Pedestrian Bridge in Netherlands
Yes, it's a delight, but how will they maintain it?

Sneek Bridge / Achterbosch Architectuur with Onix
To hell in a handbasket.

Cidade Nova Metro Station and Footbridge
Mixed feelings about this bridge in Brazil, but nice paint colour.

Kurilpa Bridge wins transport award at World Architecture Festival
No comment.

"Disaster on the Dee: Robert Stephenson's Nemesis of 1847"

2011-11-17T20:52:00.000Z

I reviewed Peter Lewis's book "Beautiful Railway Bridge of the Silvery Tay" last year, but initially approached his "Disaster on the Dee" (ISBN 0-7524-4266-X, Tempus Publishing, 2007, 224pp) [amazon.co.uk] with more trepidation.

The book tells the tale of the collapse in May 1847 of Robert Stephenson's bridge over the River Dee, built for the Chester and Holyhead Railway. The bridge had opened to rail traffic in November 1846, and five people were killed when it failed. Stephenson was heavily criticised, but went on to open the more significant Conwy and Britannia Bridges in 1848 and 1850.

The Dee Bridge spanned about 30m, and consisted of two parallel track beds, each supported by paired cast-iron girders. It was one of the longest such bridges then built, and well illustrates the dangers of pushing a proven structural form beyond safe limits. The propensity of cast iron to sudden, brittle failure was already well known, and the collapse was just one of many which dented public confidence in railway developments. It's not at first sight, therefore, such a significant bridge failure in itself as to merit book-length treatment.

Fortunately, Peter Lewis's book ranges far beyond the Dee Bridge disaster, to the extent that it's a very useful history of the structural use of cast iron, the development of metal bridges in the 19th century, and the development of railway bridges. The Dee Bridge may establish the headline, but is only one small feature in a much larger tapestry.

The Dee Bridge was an example of a so-called trussed girder, three separate cast iron segments bolted together and "reinforced" with wrought iron bars in the form of an inverted queen-post truss. The trussed girder concept was not Stephenson's, but had been introduced by Charles Blacker Vignoles some years previously. The truss bars were intended both to provide a back up against cast iron failure, and also somehow to enhance the overall strength of the girder.

Although the Dee Bridge disaster lacks the notoriety of the Tay Bridge, Tacoma Narrows, or Millennium Bridge, it has been a popular subject amongst other writers on engineering failures.

Henry Petroski's Design Paradigms (1994) uses it as a case study, "a paradigm of success masking error". Petroski draws on an unpublished PhD thesis by P. G. Sibly to show precisely the extent to which the Dee Bridge went beyond previously safe spans (click on the graph on the right) - even by the standards of its time, its calculated factor of safety against failure would have been low. Petroski attributes the failure to lateral torsional instability, noting that the almost T-shaped girders had no bracing to prevent lateral deflection; and that the eccentricity of the wrought-iron ties tended to introduce a destabilising force, as does the fact that the deck system loaded only the inner half of the girder bottom flange. The trigger for failure was the addition of 125mm of ballast load to the bridge the day before the collapse.

Lateral torsional buckling, as with any slenderness related effect, is a phenomenon which may not be an issue at all at smaller spans, but which grows in significance rapidly beyond a certain threshold. Petroski's lesson is, however, not about this narrow technical issue, but about the broader dangers of "extrapolatory design".

The bridge also features as a short case study in Failed Bridges (2010) by Joachim Scheer, who essentially follows Petroski's narrative in terms of the reasons for failure, both technical and cultural.

In Understanding Bridge Collapses (2008), Björn Åkesson devotes his first chapter to the Dee Bridge. He notes some wider technical issues. The wrought iron tie bars were unlikely to have been as effective as was imagined: the inclined bars rely on their anchorage in a "bulge" above the girder ends to work, but this bulge is prone to move inwards under girder deflections. The result is that the tie bars may have been almost entirely ineffective. Åkesson also shows that the simple rules for girder section sizing used by Stephenson (originally derived by Eaton Hodgkinson) would have underestimated tensile stresses in the bottom flange, due to the lack of any understanding of the concept of a neutral axis.

Åkesson discards the lateral torsional buckling theory on the grounds that some instability would have appeared prior to the addition of ballast, and also that the very thick girder webs would have provided sufficient U-frame action in any event. He is the only author to prevent what you might think is obvious, actual calculations for the static and fatigue stresses, which strongly suggest that static stress was far more of an issue than fatigue (an example is shown on the right). Åkesson points his finger of blame at the connections between the tie-bars and the girders, suggesting that over time, the harder material of the connecting pin would cause plastic deformation of the cast iron, and ovalisation of the connecting hole. Gradually, this would eliminate any beneficial effect of the wrought iron bars, leading to a simple tension failure once additional dead load was introduced.

I guess the genesis for Disaster on the Dee was the author's 2004 paper Aesthetics versus function: the fall of the Dee bridge, 1847. The paper, and the technical examination of the bridge failure presented in the book, make clear Lewis's background in forensic engineering, particularly metal fatigue, which he posits as the reason for the collapse. This is despite there being no surviving evidence which would support the theory (e.g. pictures of the girder crack surfaces), and a complete unwillingness to offer even the simplest of calculations. This would not have been difficult, as Åkesson's contribution shows.

Lewis discounts the possibility that failure resulted from lateral torsional buckling by stating that "this is not a failure mode, but rather a symptom of an underlying problem involving design". That's the language of a metallurgist. To a structural engineer, it's quite definitely a failure mode. Similarly, Lewis rules out failure under static overload on the grounds that the train successfully crossed several girders before reaching the one that failed, suggesting the failed girder had a prior fatigue crack. This strikes me as spurious: surely the failed girder could simply have had a defect which the others lacked, cast iron of the period being notorious for variable properties and inconsistent quality of manufacture.

The varying explanations of the Dee Bridge failure seem to indicate how strongly perceptions of failure can be influenced by an investigator's background: you find what you look for. Many years after the event, no one explanation can be proven fully correct, and they all offer useful insight into lessons that may be valid elsewhere. To me, however, the value of Disaster on the Dee lies beyond the central case study.

The book's first chapter discusses early iron bridges and gives a useful primer on how iron was cast, with particular reference to Iron Bridge in Shropshire. The next chapter explores the extension of cast iron into canal aqueducts such as those at Longdon-on-Tern and Pontcysyllte, while the third survey early railway history, including the use of iron in steam boilers. The fourth chapter covers the build-up to the design and construction of the Dee Bridge, while bringing in other structural failures in rail bridges and cast iron buildings.

After the exhaustive account of the failure and subsequent enquiries, the book goes on to look at how Stephenson's later bridge designs avoided the pitfalls which befell the Dee Bridge, and recounts many other railway and bridge catastrophes, painting a picture of an engineering industry which was slow to learn lessons from its hubris and folly. I found all these sections of the book to be hugely informative, and would recommend it for that alone.

Merseyside Bridges: 11. Howley Suspension Bridge, Warrington

2011-11-15T22:07:00.000Z

This is the last in this current series of posts, another bridge in Warrington spanning the River Mersey.

It was built in February 1912 by David Rowell & Co., who were prolific builders of many similar steel suspension footbridges. Unusually for the genre, it has been considered worthy of a Grade II Listing, although the website linked below has it by the wrong name.

A sign on the bridge states that "swinging or jumping on this bridge is strictly forbidden", suggesting a liveliness that I don't recall noticing.

I'm conscious that I know very little of the bridge's history, and as for its appearance, can only state that I am a huge fan of unpretentious, lightweight suspension footbridges such as this. So enough verbiage, here are some photos!

Further information:

Merseyside Bridges: 10. Warrington Transporter Bridge

2011-11-13T20:43:00.000Z

The last two posts were a bit of a diversion from Merseyside, not being very near the River Mersey for a start. This time, it's back to the River, although whether Warrington is part of Merseyside is perhaps a moot point.

There are plenty of bridges in Warrington, but I only had time to visit two.

The Transporter Bridge at Warrington was something of a must-see. It's one of only three surviving transporter bridges in Britain, although sadly it's by far the most neglected of the trio. It has been a presence on English Heritage's "At Risk" register for some years now, I believe.

It was originally built to service the Crosfield chemical and soap works. A railway siding to the east ended at the river bank, but wagons were transferred onto the transporter carriage and brought over the river. The rail tracks, long since disused, still run through an adjacent site. Today the site of the soap works is occupied by chemical firm Ineos Silicas, and the bridge hasn't been used since the 1960s, becoming increasingly derelict has the years have passed. Today, the bridge is maintained by Warrington Borough Council, but as it serves no practical use, it has not been well looked after.

It's also a pretty tough bridge to get to. The west abutment, within the Crosfield site, is only accessible with special permission. The east abutment involves negotiating a convoluted route through the grounds of an industrial works, or, as I did, approaching via an overgrown and somewhat forlorn pathway. The combination of lack of use and difficult access mean that any attempt to preserve the bridge for much longer may be essentially futile. I can't see how it can survive in this situation, and if it were to be relocated, that would sever the link with its historic context.

The photos make clear that this was never a pretty bridge, certainly not by comparison with its fellow transporter bridges at Newport and Middlesbrough. Its portal truss form is squat and inert, and if the latticed metalwork holds any visual attraction, it's surely only for the most committed industrial archaeologists or those besotted with the romance of dereliction.

So, it sits there and rusts. Some indication of quite how decrepit the bridge is can be gleaned from two websites with photos from unauthorised visits.

The gondola can be seen in the last photo, on the west bank, and it's still just about possible to close your eyes and imagine how it might have looked while still in active use.

Unless someone has the appetite for something radical, such as relocation, I would expect the bridge to be fenced off as dangerous within half-a-dozen years, and gone within the next decade or two.

Further information:

Merseyside Bridges: 9. Acton Swing Bridge

2011-11-08T22:46:00.000Z

From the Dutton Horse Bridge, my journey ran south along the River Weaver. The next bridge of significance gives its name to the small town of Acton Bridge.

It was designed by the same John Arthur Saner who designed the Dutton Horse Bridge, and apparently many other structures along the River Weaver. The current bridge opened in 1933, replacing a previous structure which had been able to carry only one line of traffic with an axle weight limit of 8 tons.

It is 83.5m long, with two slightly skew spans of 25m each. It's estimated cost at the time of construction was £52,000, excluding the diverted approach roads. The superstructure comprises twin riveted steel trusses, supported on a mass concrete pontoon chamber. One website describes it as "the first floating swing bridge in Britain", although I think there is some confusion there with the nearby Northwich Town Swing Bridge, which has a plate on it claiming it to be "the first road swing bridge on floating pontoons".

In its structural form it is typical of many truss swing bridges of the period, and not as elegant as some. The overhead bracing seems particularly over-designed. The curved profile of the truss is visually satisfactory but does not optimise the level of stress in the main members. Structurally, this particular profile's main benefit is to keep the overhead bracing clear of vehicles.

The use of contrasting black-and-white paint is common to many of the structures along the River Wear.

With the truss main members and verticals painted white, and the diagonals black, there seems to be an intention to define a visual hierarchy of members and perhaps de-emphasise some. There is no great structural logic behind this, as the diagonals are as important to the bridge's overall strength as the verticals.

The edge of the bridge deck is painted with black and white bars, presumably to warn of limited headroom. Interestingly, the footway parapets are painted with the same alternating pattern. This makes the parapet appear to dissolve into a series of isolated panels with open gaps between them, which is a peculiar effect, if intentional.

Further information:

Google maps / Bing maps
movablebridges.org.uk
British Bridges: An Illustrated Technical and Historical Record (Public Works, Roads and Transport Congress, 1933)

Merseyside Bridges: 8. Dutton Horse Bridge

2011-11-04T21:43:00.000Z

This is a short detour from Merseyside, however broadly that area might be defined. From Runcorn, the journey heads south-east towards Northwich. I stopped off at two bridges before returning north to the River Mersey. In broad outline, this route follows the course of the River Weaver, which is a tributary to the Mersey.

The first of the two structures is Dutton Horse Bridge. This twin-span timber bridge was completed in 1919 to a design by John Saner, who was the engineer responsible for many works along the River Weaver when its navigability was improved. The Dutton Horse Bridge spans alongside the river's main course, over a secondary channel used to help regulate the water level.

It is historically significant as one of the earliest surviving bridges to feature laminated timber. The laminated arches span about 31m, with two ribs slightly out of line with each other. Triangulated timber struts stiffen the arches and support the deck.

As with many timber structures, it's certainly an attractive bridge, and it's great to see it has survived so well. Two span bridges are reputed to suffer from the problem of the "unresolved duality", where the viewer lacks a primary visual focus and so feels discomfited. This is a phenomenon that has received support from at least one experimental study, where viewers consistently tended to prefer one or three-span bridges to those with two spans. At Dutton, the bridge is rarely seen in full elevation, as the footpath on the opposite side of the river seems not to be the main route. From any other angle, the number of spans is hardly relevant. Even in full elevation, I think it looks fine.

The black-and-white paint scheme is characteristic of several bridges along the Weaver, including the one I'll come to next.

Further information:

Google maps / Bing maps
Engineering Timelines
British Listed Buildings
An Encyclopaedia of Britain's Bridges (McFetrich, 2010)

Amsterdam Iconic Pedestrian Bridge Competition

2011-11-01T09:56:00.000Z

An open international contest has been announced to design an "iconic" [ugh] pedestrian bridge in Amsterdam.

Apparently, the architecture of the bridge should "reflect contemporary design tendencies", whatever they may be. Perhaps that means they want a bridge which looks like a turd shat by a giant penguin across a canal.

It's a single stage contest: to enter, you simply have to pay the registration fee (US$80 until 15th December, rising to US$120 until 15th February) to receive full contest details.

The winner gets a US$3,000 prize, there are smaller prizes for second and third, and there will be seven honorable mentions. Winners will be announced on 15th March 2012.

They emphasise that "there are no plans for the Iconic Pedestrian Bridge to be built." The site for the (imaginary) bridge, which would be about 90m long, is in front of the Amsterdam Heritage Museum, spanning the River Amstel. No engineering calculations are required, instead the structural design is suggested to be "architectonic" in nature. The biggest geometrical challenge is that a 15m navigation headroom is specified.

The competition is organised by AC-CA (Architectural Competition Concours d'Architecture), a private company whose business seems to be running contests for designs which will never get built, the architectural equivalent of vanity publishing.

I really must get back to writing up some more Merseyside bridges to post!

Merseyside Bridges: 7. Silver Jubilee Bridge

2011-10-26T21:26:00.000+01:00

Righty-ho, from Liverpool, this tour heads inland, following the course of the River Mersey, although with a sharp detour coming up soon.

In Liverpool, there are no bridges across the river, only tunnels below it. Heading east, the next opportunity to cross comes between Runcorn and Widnes. The River was first spanned here in 1868 by William Baker's Runcorn Railway Bridge, with three 93m spans, bridged by wrought iron lattice girders. It's visible in several of the photographs.

The second bridge here was the Widnes-Runcorn Transporter Bridge, opened in 1905. This was the first (and longest) of the only four transporter bridges to be built in Britain. In July 1961, the bridge now known as the Silver Jubilee Bridge was completed (originally the Runcorn-Widnes Bridge), with the transporter bridge being demolished immediately thereafter.

This was designed by Mott Hay and Anderson, at almost exactly the same time as they designed Tamar Bridge. As I noted a month ago, the two bridges make for an interesting comparison. The Runcorn-Widnes Bridge spans 330m, while the Tamar Bridge spans 335m. Both structures are in close proximity to a historic railway viaduct, but very different solutions were chosen.

Three-span and five-span truss designs were considered for the Runcorn-Widnes crossing, but rejected in favour of a suspension bridge design. However, wind tunnel tests showed that eddies in the wind caused by the proximity of the Runcorn Railway Bridge could destabilise the suspension bridge, and it had to be redesigned with an unusually stiff deck to prevent this. Nonetheless, the client eventually preferred a steel arch bridge option. At Tamar, the opposite conclusion was drawn when it was shown that the height of the road bridge deck relative to the railway bridge sufficiently reduced the effect of wind eddies.

The arch design was not without its problems. A two-pinned arch similar to the Sydney Harbour Bridge was shown to have a natural frequency of vibration not dissimilar to the rejected suspension bridge option. Making the bridge continuous with its side-spans altered the frequency sufficiently to resolve this concern, and offered the added benefit that the arch could easily be built by cantilevering from either side. Two very similar bridges built in the 1960s were the Bridge of the Americas (344m span, 1962) and Laviolette Bridge (335m span, 1967).

One aspect of the Silver Jubilee Bridge's construction which was perhaps surprising for the period was that it was built from riveted steel, a method essentially then obsolete. It was certainly one of the last, if not the last, large bridge in the UK to be riveted.

Any attempt to judge the aesthetics of a bridge like this might be considered irrelevant. The form and appearance are determined almost entirely by considerations of load-carrying function and of the demands of construction. Nonetheless, the not dissimilar Sydney Harbour Bridge and Tyne Bridge (the latter also designed by Mott Hay and Anderson) have both become city icons in spite of their industrial appearance. The Silver Jubilee Bridge is less iconic but much of that is down to context: power stations and chemical plants define much of the landscape of Runcorn and Widnes, and the Silver Jubilee Bridge seems an inevitable consequence of this rather than something which stands alone.

Its closeness to the railway bridge renders it difficult to see in isolation, as will be apparent from the photos of the main elevation. I find the choice of colour unconvincing as well, it's a little sickly and not really in keeping with a bridge where its sheer scale means it dominates the largely flat landscape. A difficult bridge to love.

Further information:

Google maps / Bing maps
Wikipedia
Structurae
English Heritage
Engineering Timelines
OUBE
28 Days Later (some photos of the bridge from an unusual perspective)
Modern British Bridges (Henry & Jerome, 1965)
Civil Engineering Heritage: Northern England (Rennison, 1996)
Bridging the Mersey: A Pictorial History (Thompson, 2000)
Bridging us Together: the Story of the Runcorn-Widnes Bridge (Thompson, 2001)
Silver Jubilee Bridge (Knight, 2007, student paper)
An Encyclopaedia of Britain's Bridges (McFetrich, 2010)

Merseyside Bridges: 6. Paradise Street Bridge, Liverpool

2011-10-23T22:44:00.097+01:00

Wilkinson Eyre built their reputation as specialist bridge design architects with a series of spans where the art of structural engineering was allowed to be the star. The architect's skill lay in pushing the engineering outside its normal comfort zone, in establishing a sense of sublime poise, and in ensuring quality of detailing. Paradise Street Bridge, in Liverpool, represents a major departure from that approach, although not the only such example in their portfolio.

Designed in collaboration with Arup, this £2.4m covered footbridge links a multi-storey car park to a John Lewis department store. The span, approximately 60m, is unusually large for such a structure, although certainly not the longest (the Ney & Partners bridge at Esch-sur-Alzette spans further).

Images of the bridge that I had seen before visiting it were oddly disturbing. The bridge's lack of lateral symmetry appeared forced, with little in the way of obvious logic. From above, a better sense can be obtained of how it works. The bridge kinks to either side of a central axis, but is rotationally symmetrical, with glazing offering views in and out in the areas furthest from the main axis.

A similar sense can be obtained from below. It's more ordered than the crumpled-paper architecture of Frank Gehry, it has more in common with the crystalline geometry of Daniel Libeskind, but it's still more than a little uncomfortable in its disdain for rationalism. While you begin to get a sense of how it works structurally (it's a varying section steel box girder supporting a set of clad and glazed frames), it refuses straightfoward comprehension.

It becomes clear that it's a skewed, distorted cousin of Wilkinson Eyre's earlier Bridge of Aspiration, which introduced the basic idea of a disguised box girder supporting a series of continuously varying frames. It's only when you go inside the bridge that it really starts to make any sense, as it's immediately clear that the outlandish geometry is there simply to obfuscate the possibility of a simple linear crossing, where you can see from one end to the other where you are going, and consequently focus on your destination more than on the journey.

At Paradise Street, there is no clear view from end to end, and instead your attention is drawn to the geometry of the enclosed space, and its relationship to the world beyond. The varying angles of the bridge relative to the sunlight allow the already peculiar geometry to project new patterns against itself, varying with time, season, location and orientation.

As a piece of structural engineering, I hate it - if the relationship between engineer and architect was truly collaborative, that's nowhere made visible. As a way to walk between a multi-storey car park and a department store, it's an interesting and unusual experience.

Further information:

Google maps / Bing maps (current views pre-date bridge construction)
Wilkinson Eyre

Merseyside Bridges: 5. Stanley Dock Bascule Bridge, Liverpool

2011-10-20T23:45:00.083+01:00

My Merseyside journey continued south from Bootle into the centre of Liverpool. Travelling along Regent Road, I crossed the entrance to Stanley Dock via this bridge. It's of the Scherzer Rolling Lift type, a patented design where the bridge deck rocks back onto a roller girder in order to raise it to allow vessels to pass through. It's a little like a rocking-chair, pulled back by mechanical arms.

I've previously reported on a twin-leaf example of the genre, Queensferry Bridge, although that is no longer able to open. The bridge at Stanley Dock has only recently been refurbished, at the cost of £600,000. It was originally built in 1932, and allowed to run into disrepair by the owners, Peel Ports, leading eventually to its closure in May 2008. In 2010, repairs were carried out, the machine house re-roofed, and everything given a lick of new paint. The work won a Historic Bridge and Infrastructure Award earlier this year.

The rolling girder can be seen in the photo, complete with copious riveted stiffening - the entire bridge sits directly on this when it opens. One advantage of the arrangement is that the centre of gravity changes position with respect to the point of support - the counterbalance can be adjusted to make sure that when closed, the bridge tends to stay open, and when fully open, it tends to stay that way. The photo also illustrates one of the things I like most about bridges of this vintage - you can't escape the visual evidence of its making and assembly. Modern bridge technology tends to erase rather than emphasise this aspect, and such bridges often appear as if wished-into-place without having experienced any birth pains.

The bridge's machine room spans the roadway, and is something of a blot on the landscape, although not without character. I've included a couple of links at the end to websites with photos of the interior.

The bridge isn't unique, even locally, as there's a very similar span, Egerton Bridge, on the other side of the Mersey at Birkenhead, although I didn't get to visit it on this trip. Examples elsewhere in the UK include those at Barrow-in-Furness, Inchinnan, Keadby and Poole.

The bridge sits amidst some spectacular disused dockside structures, most notably the absolutely enormous Stanley Dock Tobacco Warehouse building visible in the final picture. There is still a lot of industry nearby, but much of the area is derelict. It's clearly ripe for some kind of Docklands-style redevelopment, but presumably the money simply isn't there.

Further information:

Google maps / Bing maps
moveablebridges.org.uk
28dayslater (photos before and during refurbishment, and inside the machinery room)
Northwest Exploration (photos inside the machinery room after refurbishment)
MC Construction

Merseyside Bridges: 4. Pennington Road Footbridge, Bootle

2011-10-19T20:42:00.002+01:00

Ok, heading south along the coast from Southport, we come to Bootle, at the northern end of Liverpool.

In 2006, RIBA organised a bridge design competition for a replacement of a rather grim pedestrian bridge spanning the Leeds to Liverpool Canal in Bootle. They received 88 entries (some of which I've shown here before), and in early 2007 announced the winning design, from Softroom and Eckersley O'Callaghan.

Out of seven RIBA bridge design competitions that I considered in July 2009, this is the only one which has resulted in a bridge actually being built. Such a rare specimen clearly merits close attention. Several of the RIBA bridges foundered over funding, either because there never was any, or because of unacceptable cost increases. The Pennington Road bridge suffered from the same issue, costing £750k to build against an original budget of £400k. That's a very large sum for what is basically a very short span pedestrian bridge, so someone must have thought it was worth it.

The bridge spans east-west across the canal. At its east end, it ramps straight down to ground level. On the west side, the deck spills you out onto the top of a large mound, which can be descended to the west and south by staircases. Between the staircases, there are a series of switch-back ramps, some of which you can see on the right of the photo (click on any image for a larger version). This is a fairly horrid solution to providing mobility-impaired access, and it's far from clear that there wasn't enough space for a more direct ramp arrangement.

When it was built, the ramps had slopes with planting on them, currently being rebuilt in block-paving, presumably a response to vandalism, although not one that improves the bridge's aesthetic.

The staircases are bordered by timber walls, which give the impression of flowing seamlessly into the timber beams which carry the main bridge deck. The trough-type deck is bounded by two glulam timber beams, but the timber continuing down the ramps and stairs is essentially cosmetic.

These timber parapets support a handrail and also a post-and-wire fence. I'm not sure whether this is to provide a required balustrade height, or just to stop people skateboarding along the top of the parapet beams. I do like the jagged relationship between the handrail and parapet on the staircases.

The floor of the bridge is in timber as well, and I have to say it's great to see timber being used on such an "architectural" bridge. I can imagine there were a few questions asked about durability, resistance to vandalism, and fire risk, but the wood has worn well so far, with very little visible damage (although a number of recessed light fittings have been broken, unsurprisingly).

From underneath, the structural form is perhaps clearer. It's also possible to get an idea of the original, unweathered colour of the wood, which is much warmer in tone. I think this is one aspect of the bridge which is a little unfortunate: wood is often commended for its organic approachability, but as it silvers with age it does lose a lot of what initially makes it attractive. A darker timber may have worked better, as from above, the bridge does now look cold and washed-out.

You can't really tell from the soffit photo, but if you squint at the first photo you can just about see that the main span is simply supported at either end on very small lugs, which project out from the concrete abutments (this is made clearer on some of the images at the Eckersley O'Callaghan website linked below). Initially, this offended my structural engineer's sensibility, that the structural form and the geometric form should be closely partnered - the deck supports break up the sense of visual flow. However, it's a reasonable compromise in achieving the architect's concept, so nothing to worry about.

I was left with a sense of appreciation for the bridge's modesty. It has been built in a slightly run-down area where functionality and robustness are laudable aims, and it rightly avoids a level of flash that would never have suited the site.

Further information:

Google maps / Bing maps (both sites currently show images pre-dating the construction of the bridge)
Softroom
Eckersley O'Callaghan (includes images from design development and construction)
Wrenco
RIBA competitions

Bridges news roundup

2011-10-18T21:34:00.007+01:00

I thought I'd briefly interrupt the posts on Merseyside bridges to catch up with some bridges news from the last week or two ...

Happy birthday to a transport of delight
Middlesbrough Transporter Bridge celebrates its centenary. Nice little article from The Guardian.

Barnard Castle footbridge would be 'longest in UK'

265m suspension footbridge proposed. Close examination of the image supplied suggests a commendable desire to keep to keep it cheap and cheerful rather than unnecessarily embellished. I think that's a good thing, and it would be a remarkable span if they can only work out how to fund it.

Crazy Swiss Swingers Suspend Hot Tub from Bridge
Yes, yes, but which bridge is it?

Rehberger's Slinky Footbridge

Designer of new footbridge in Oberhausen interviewed. It was designed in collaboration with Schlaich Bergermann, and the artist's spiral enclosure notwithstanding, it's an impressive stressed ribbon bridge (the deck for the main span is 66m long and a mere 12cm thick). It's almost a shame, given the inspiration, that it doesn't appear to wobble. More details here.

Thousands of jobs secured as Mersey Gateway gets green light
This has been extensively reported elsewhere, but I thought a couple of points were worth noting. Can we take seriously the project director's quote that "Only six organisations in the world are capable of delivering this complex project." Really? Really? The local councils' chief executive also said: "We will keep the iconic design of the bridge but we will be challenging engineers to come up with different ideas and designs." It will be interesting to see what that means when tenders are submitted: there would seem limited scope for contractor value engineering unless at least some significant variation on the current design is permitted.

Pihl is building new bridge in Copenhagen

Danish contractor Pihl have been awarded the contract to build the Inderhavnen "Kissing Bridge". I've discussed the design, by Flint and Neill, Studio Bednarski, Hardesty and Hanover, and Speirs and Major, previously. It's an unusual opening bridge where the two halves of the main span retract along curved guideways.

Pennine Bridleway bridge design gains plaudits

It's an environmentally appropriate and structurally remarkable timber footbridge, built in the Yorkshire Dales, and already receiving awards. Its 24m main span is in stress-laminated timber, with short lengths of timber in laid in the form of an arch, and tensioned together with transverse tie rods. The pictures at outdoorsmagic.com make that a bit clearer. It has been recognised with a Wood Award and a BCIA Award.

City release new renderings of ped-bike bridge

Knoxville, Tennessee are planning a major river crossing, with the 200m span arch depicted being the preference from six options discussed in a detailed report. It's hard to believe it's the least expensive, and the arches as currently shown look unnecessarily bulky (possibly because they seem to want to do it in concrete rather than steel).

Council chief says ‘bold design’ of bridge will create ‘distinctive’ gateway to the city
Work to start on landmark Bradford footbridge. Bold, yes. Beautiful? Nah.

Merseyside Bridges: 3. Venetian Bridge, Southport

2011-10-17T22:45:00.000+01:00

There are three bridges which cross the artificial lake in Southport. I've already covered the first two, and the third is here for completeness rather than special interest. It has three sections, separated by two islands, all built in 1931, with concrete main structural members supporting a timber deck. They were refurbished in the early 1990s.

Further information:

Merseyside Bridges: 2. Marine Way Bridge, Southport

2011-10-16T21:49:00.000+01:00

Marine Way Bridge lies right next to Southport Pier, the subject of my last post. The contrast is remarkable. It's perhaps unusual to find a landmark bridge of this size located quite so centrally in a predominantly low-lying urban area.

Opened in 2004, Marine Way Bridge carries a local road across an artificial lake, which dates back to 1887. As well as improving highway links, it sought to provide a "catalyst for future investment and regeneration" in what is a somewhat run-down seaside resort. A previous road bridge had been demolished 15 years earlier, and the new bridge restored a key connection between the seafront and the main part of the town.

It's an asymmetric cable-stayed bridge, with the deck supported from an A-frame pylon sitting to one side of the lake channel. It has a main span of 80m, and is 150m long and 18.5m wide. The tower is 56m tall. Both the deck and the pylon are in reinforced concrete.

The bridge was designed by Babtie (now part of Jacobs) with Nicol Russell Studios, and built by Balfour Beatty. It shares a number of similarities to Nicol Russell's previous Leven Crossing bridge at Glenrothes. The design was reportedly the winner of a competition, although I've not found any details on that. The bridge won the ICE's North West Merit Award in 2005.

Seen in elevation, the tower gives the impression it is taller than it needs to be, with the forespan cables steeper than is normal in a cable-stay bridge. A 40m tall tower would be sufficient to get the average cable angle at 45°, which is more conventional. It's not clear whether the height was chosen to reinforce the structure's landmark status, or to reduce the horizontal forces in the deck, and hence on the foundations.

I never really like A-frame pylons, visually. I can't quite figure out what it is about them that I dislike. At Marine Way, an effort has been made to shape the head of the tower, but the legs themselves are still a bit too bland.

The underside of the deck is more successful, taking the form of a concrete ladder beam with two large edge beams and a series of crossbeam ribs. It's more attractive than the underside of many bridges, but from an engineering perspective, the crossbeams seem unnecessarily deep, and the whole thing just too heavy - a steel structure would have considerably reduced the cost of the foundations.

From above, the decision to anchor the cables directly into the edge beams, rather than through small cantilever stubs, seems a little unfortunate. It creates a level platform likely to attract people to hop over the main parapet, and hence needs protecting with awkward cables, as shown.

On the whole, it's certainly not an unattractive cable-stay bridge, but it does strike me as a little out of place, especially set against the other bridges which span this artificial lake (I covered one last time, and the other will be my next post). There seems no pressing reason to have to span the lake without intermediate piers, and an attractive bridge could have been designed which was far less expensive. Whether the bridge fulfilled its aim to act as a catalyst for regeneration, although looking at the surroundings, I doubt there is much that a more modest bridge wouldn't also have facilitated.

Further information:

Google maps / Bing maps (image taken during construction)
Structurae
Aerial photo taken during construction
Sefton Council
Stirling Lloyd

Merseyside Bridges: 1. Southport Pier

2011-10-13T23:24:00.002+01:00

Okay, before embarking on a set of reports from a tour of Merseyside, I ought to point out straight away that I'm using the term in its broadest sense, a sort of Greater Merseyside which stretches from Southport in the north, along to Warrington at its easternmost extremity. I know locals get touchy about these designations, but really, it's just an excuse to go visit some interesting bridges and lump them all together here, okay?

I think Southport Pier is the first pier that I've featured here. Is a pier a bridge? A pier is clearly bridge-like in its structural form if not in satisfying the usual definition of "spanning an obstacle". Southport Pier, however, makes the decision easy, as not only does it jut out into the sea, but part of it also spans an artificial lake. So it's definitely a bridge.

It was designed by Sir James Brunlees, and opened in 1860. At 1108m long, it's the second longest pier in Britain, although a large part of its length is over land. It was even longer in the past, having been extended first in 1864, and then again in 1868. From the point of view of engineering history, its use of jetted piles was pioneering, but I'm afraid I just can't get that bothered about piles.

It was proposed to be demolished in 1990, but saved and Listed (Grade II) following a vigorous campaign. I find it hard to fathom why a seaside resort like Southport would want to demolish one of its main attractions, and I think they were perhaps swayed by unrealistic estimates of the cost of maintenance (a figure of £250,000 for repainting every 5 years was quoted).

One of the methods used to help save the pier was by a campaign to sponsor the planks in the deck, the legacy of which is clearly visible via individually named plates embedded in each plank.

The pier is described as having been refurbished, with the work completed in 2002, but it's clear that large parts of it were completely rebuilt. Looking close up at the main lattice beams, it's apparent they are welded, which clearly isn't part of any original construction. The current aerial image shown at Bing (linked below) also makes clear how extensive the rebuilding was. I guess the cast iron columns and wrought iron tie bar bracing may be original, and for me these are the main attraction of the pier - their delicacy is what makes it an attractive structure, as the modern decking and parapets, and the awful arched lighting supports, are certainly not very appealing.

The pier also carries a unique battery-powered tramway, added in 2005. The links below provide far more information on the pier's history than it would be sensible to recount here.

Further information:

Google maps / Bing maps (image taken during reconstruction)
Wikipedia
Structurae
Engineering Timelines
the-pier.co.uk
National Piers Society
The Heritage Trail
Southport Pier Trust article on restoration
Civil Engineering Heritage: Northern England (Rennison, 1996)

Where are they now? Part 4

2011-10-12T23:25:00.002+01:00

Okay, I did three previous posts where I looked back at some of the bridge schemes I had covered in previous years, asking what had happened to them after I had mentioned to them. Here is the final such roundup, for now at least.

Kraków Footbridge

Now, here was a fine one. The winner of a 2006 design competition was much panned at the time, largely because its architect had designed something that couldn't possibly stand up. In November 2009, I noted the project had undergone an interesting metamorphosis, with the ultra-slender concept being substantially fattened up until a structure emerged which could actually cope with iniquitous gravity.

At the time, I commented that funding seemed uncertain, but there has clearly been enough money in the pot to treat the design very seriously indeed. There were a couple of papers at the recent Footbridge 2011 conference on the Kazimierz-Ludwinów bridge (to give it the proper title), both from the architect and the engineers. These showed clearly that considerable effort has gone into the structure's development, and I've used an image from one paper as the illustration (click to enlarge).

The engineer's paper reported that the bridge had a PLN 37m budget, but that the lowest tender received in 2009 was PLN 3m above that, leading to the scheme's cancellation. I'm not sure, however, whether that is the end of the story, or whether there is more life in this project yet.

St Patrick's Bridge, Calgary
The main bridge story in Calgary has been Santiago Calatrava's Peace Bridge, which has been a fiasco from beginning to end, except for the fact that the sorry tale seems so far to have no end in sight. I last discussed it extensively in April, reporting on delays caused by shoddy welding.

The footbridge scheme at St Patrick's Island was always seen as its better-organised neighbour, procured through an open design competition, and won in March 2010 by a bridge which obeyed the laws of structural common sense (pictured, design by Halsall and RFR).

That's pretty much all I can report. The bridge concept was approved by a city committee earlier this year, but I haven't seen any other news. The promoter's website suggests construction will start before the end of 2011, but I haven't seen any sign that construction tenders have been invited yet.

Four Mile Run
I was accused of being a little unkind to the US bridge design competition at Four Mile Run, when in November 2009, I used it as an example of "How not to run a bridge design competition". Amongst my complaints were the lack of any engineering information or justification for the structure; an opaque judging process; the lack of guidance as to what the promoters actually wanted; and the fact that no funding appeared to be in place to actually appoint a designer, let alone build the bridge.

In April 2010, the three contest winners were announced, with a proposal by Arup and Grimshaw coming top. I was too busy at the time to say much about the top three designs, all of which can be seen on the competition website. Since that announcement, the contest website has not been updated and I could find no further news, none of which is any surprise given how the competition was set up.

Since I was so remiss at the time, here are the three shortlisted designs:

Arup / Grimshaw / Scape

Olin / Buro Happold / Explorations Architecture / L'Observatoire International

Rosales + Partners / Schlaich Bergermann / Simpson Gumpertz and Heger

New Royal Victoria Dock contest
Very near the end of 2009, I discussed a "competition" being held for a proposed new crossing of Royal Victoria Dock in London, to improve pedestrian access to an exhibition centre during the 2012 London Olympics. Entrants were being sought via an odd sort of competitive interview where teams were set a design challenge and observed in how they responded to it. I never covered the subject again.

It turns out that the contest was won by Ian Ritchie Architects and Atelier One. They came up with several ideas, such as pontoon structures and opening bridges, as well as the one pictured here, described as a "water boatman" bridge, essentially a ferry or cable-car structure re-imagined in rotational rather than translational space. Apparently, all involved with the scheme agreed this was the option which would be taken forward, but pressure on Olympic project costs then led to the entire scheme being cancelled.

Blogs roundup

2011-10-11T21:24:00.000+01:00

It's time for a quick roundup of what you can read about bridges on various other blogs, as something of a stopgap before I embark on a set of reports covering nearly a dozen bridges in the Merseyside area, as well as catching up on several posts that I've had gestating for some time now.

Tallbridgeguy and Bridge Photo of the Day form something of a triumvirate of the more prolific bridge blogs (together with this one, of course).

TBG is the most diverse, with everything from off-the-wall design concepts through to the sort of practical day-to-day issues that actually take up an engineer's time. It even strays away from bridges quite a bit - I have a self-imposed rule not to do so (simply because I spend more than enough time on bridges without getting distracted!) TBG also writes the Google Sketchup for Engineers blog.

BPHOD is the Ronseal of the two blogs, often featuring bridges chosen from fact-finding trips around the world to areas which have been hit by earthquakes, which in recent months means India and New Zealand.

Tabikappa is a similar blog from Japan, although with a focus on photographs of bridges, hardly ever much text. They've been quiet recently, but returned with a quite marvellous double lenticular truss bridge.

ArchDaily chucks out posts like bullets from a machine gun, corpuscles of architectural gloss splattered across an internet canvas. They featured a bridge recently, Caltrava's Bac de Roda highway bridge, one of the Spanish designer's earlier and hence marginally more orthodox designs.

It's not a blog, but a monthly email, but Bill Harvey's Bridge of the Month is often interesting. Bill is an expert in masonry arch bridges, and generally finds an interesting technical angle on the bridges he covers. The most recent issue features Pyne Bridge, a very unusual set of brick arch spans supported on granite columns.

I can also recommend Bridgink's Bridge of the Month, a monthly "name that bridge" quiz with a book given away to one of the successful entrants every month.

Finally, tired of all these bridges? Perhaps you need to refresh yourself with the blog from the British Water Tower Appreciation Society. Or lift your head up high with the Pylon of the Month blog.

Manchester Bridges: 18. Media City Footbridge

2011-10-09T23:00:00.000+01:00

I had been waiting to find out when the new Gifford and Wilkinson Eyre-designed Media City Footbridge in Manchester was due to open to the public, only to discover on a chance visit at the end of September that it was in fact already open.

It's an asymmetric bobtail swing bridge, spanning across the Manchester Ship Canal. It's 83m long overall, with a 63m main span. To the north, it provides access to the new Media City development in Salford, the new home to several departments of the BBC. On the south bank, it currently connects to the Imperial War Museum North, but will eventually link in to a new ITV studio development.

The bridge deck is supported by a harp-style cable-stay layout. The cables support one edge of the deck, and connect to eight steel masts in a fan arrangement which I previously likened to a giant skeletal hand. I think perhaps the design visualisations were a little unflattering, as now that I've seen the (nearly) finished structure, it is a much more attractive creature.

The odd assemblage of masts arises from the formalism of the geometry. The cables establish a harp arrangement in elevation (i.e. they are parallel when viewed from that angle), and are tangential in plan to the curved edge of the deck. This creates a geometry where the cables must be supported at eight separate positions in space, rather than from a single mast.

The supported edge of the deck is a deep triangular steel box girder, paired with a shallow box below half of the deck itself. These provide the necessary torsional and bending stiffness, and support the other half of the deck via a series of cantilevered ribs, visible in the photo (click on any image for a full size version). The alignment of the edge girder is not quite perfect, but I don't imagine the casual observer will notice. The image also shows the flared width of the backspan, which conceals a concrete counterweight used to balance loads on the pivot pier.

The sharp edge of the box girder is such that it's depth is almost completely disguised, with the upper surface appearing as a streamlined fascia, and the lower surface disappearing into shadow along with the rest of the bridge soffit. On the face of the girder adjacent to the deck, glazed panels act to obscure it, and these conceal light fittings which help illuminate the deck at night and distract further from the beam's structural mass.

The cables connect the masts to the rear of the back-span, and the anchorage points have been adapted to provide jaunty little seats. Between the anchorages, users can walk straight into the future ITV site, although the steps and handrails were still under construction when I visited. People walking towards the Imperial War Museum bypass the anchorages completely. The detailing of the anchorages and seats is very nicely done. In the background of the photo you can see the Museum on the right, and on the left is the Lowry Millennium Bridge, which I've visited previously.

As with many Wilkinson Eyre designs (see for example South Quay and Swansea), a conscious effort has been made to treat the two bridge parapets differently. I've already mentioned the east parapet, which does an impressive job of hiding the main deck girder. While I was on site, there was at least one panel of the lightbox where the glass had shattered, and several more temporarily dismantled - I'm not sure whether this was to work on the glass or on the light fittings. This is a reasonably well-used and well-policed location, so I would hope that vandalism isn't a recurring issue.

The west parapet is a post and rail system in stainless steel, with some lighting concealed in the uprights. You can also see in the photograph above right how the deck surfacing is divided, with a resin/grit finish to the underlying steel box girder on the right, and aluminium decking panels on the left.

One element of the bridge I particularly like is the detailing of the mast pedestal (the large silver cylinders are uplighters). Each mast sits on a stainless steel ball bearing. You can also see the bottom edge of the mast, which is lens-shaped in cross-section. The cigar-like masts have been cut, bent and re-welded from basic circular hollow sections, and I think the result is visually very attractive.

Not all the detailing is perfect. I particularly disliked the cover plate to the north expansion joint, which is in two hinged sections to be manually flipped out of the way before the bridge is opened. It looks like an afterthought rather than something properly considered.

The bridge's main visual feature is the way the mast and cable array changes as it is viewed from different perspectives. The simple harp-like arrangement of the cables is clear only from the main elevations, and from other angles it is clear that their geometry is much more complex. The photo above right shows that they appear warped when viewed from the north end of the bridge.

Not every part of the bridge adjusts to changing perspective so well. The deck's vertical curvature is a careful compromise between canal navigational clearance demands and the geometry of the canal banks, with the deck ramping down at 1:15 to meet the ground. While the curve looks gentle from most locations, the S-shaped curvature of the west edge of the deck is such that in a foreshortened view, the deck looks to have broken its back. The same thing can be seen on the Tradeston Bridge in Glasgow, which shares the S-curve in plan. I doubt that anyone other than over-fussy bridge designers will spot it, however.

Quibbles aside, I was very pleasantly suprised by the Media City Footbridge. I had completely underestimated the quality of the design beforehand. I would now say it is well up there amongst the best major pedestrian bridges built in the UK in modern times, a genuine rival to the same design team's Gateshead Millennium Bridge. It has been shortlisted for an Institution of Structural Engineers Award, and deservedly so.

Further information:

Google maps / Bing maps (current images pre-date bridge construction)
Wilkinson Eyre
Gifford
Atkins Bennett / Eadon Consulting
KGAL
Rowecord
Media City Footbridge, Salford Quays (Curran & Thompson, IABSE Symposium 2010)
Media City Footbridge, Salford, UK (Marks, Thompson & Curran, IABSE Symposium 2011)
Media City Footbridge, Salford Quays (Curran & Thompson, Footbridge 2011)

Kruunusillat contest suspended

2011-10-05T20:19:00.000+01:00

I see from the BD&E website that the Kruunusillat Bridge Design Competition, for a new light rail link in Finland, has ground to a halt. Apparently, an appeal by one of the teams has resulted in Finland's Market Court suspending the contest. A delay of two to twelve months is now forecast. I previously discussed the competition here.

52 teams had submitted prequalification entries. Seven of those had been disqualified for various reasons, and the remaining teams had been notified of how their entry had been scored, with the expectation that a shortlist of ten competitors would be announced at the end of September to move forward to the next stage.

Having seen the detailed judging panel comments and scoring for all the entrants, I was all set to post some comments here on who had been selected, and who had been left out. There were some surprising scores, to say the least, with some very experienced and capable entrants ranked well below less well-known teams. Some teams made multiple entries, and I'm aware of one engineering firm who were rated with a score of 200 for their engineering capability in one entry, but only 20 in another.

Many of the comments from the judges seemed poorly matched to the scores actually given - one very well known architect received a high score for their aesthetic capability despite being criticised for their insensitivity to bridge structures in the accompanying text.

The way the entries were judged seemed to favour the capabilities of individuals with a well-stacked CV over the capabilities of a broader team. That was always a bizarre approach to take.

I don't know who has scuppered the whole process but would have thought that some of the disqualified entrants would have been very surprised to find themselves in that position.

It will be very interesting to see what further news emerges. I imagine there are many disgruntled contestants beyond the one firm which went to the court. Would any of my readers care to click the comment button to provide further feedback?

Fisherman's Bridge, Cumbria

2011-10-05T00:10:00.000+01:00

I had been waiting for a chance to visit this bridge for several months, and was glad to finally see it even if the weather was rather dismal. It's easily a favourite amongst the many bridges I've featured here on this blog.

Fisherman's Bridge is remarkable in many ways. It's not a large structure, spanning only 15m, and a mere 0.9m wide, but it's still quite staggering that it was built for the tiny budget of only £18,000.

It sits on private land in the Duddon Valley, in the Lake District, providing access for an occasional angler across the River Duddon. It's almost impossible to spot from the public highway.

Structurally, it is almost absurdly simple, a simply-supported weathering steel box girder, triangular in elevation and in cross-section at mid-span. I think it's fair to say that it's design hasn't been limited by the standard 5kN per square metre load normally used in the UK.

The structural engineer was Rob Nilsson of Price & Myers, while the architect was Ralph Parker of H-o-n-e-y.

Similarly, the balustrades, intermittent steel rods carrying a tubular handrail, comply with none of the usual requirements, being both easy to fall through, and easy to wobble. That's a good thing, I think.

The rods alternate either side of the handrail to provide some stiffness, but also give a first impression that the bridge has been assembled in a haphazard, jumbled manner.

The steps at either end consist of slate slabs set in concrete, and attempt to raise the bridge clear of the river's flood level. However, the video below, made in November 2009, makes clear that it is not quite high enough!

Original on vimeo

That's pretty impressive, especially when you see how the bridge is attached to its supports, with simple, slender vertical plates.

There are some elements of the bridge which appear unfinished, chiefly the way the parapets are painted rather than in exposed weathering steel like the rest of the structure. It's like a piece of rusty old farm machinery which has been dragged to the bottom of the field and dragged across to span the river.

When I first saw a picture of the bridge, I was disappointed by the triangular rather than curved profile, but up close, quibbles dissolve. It's an entirely singular structure, although I am reminded a little of a similarly rusty, non-standard private footbridge in the US.

You can click on any photo for a larger version, and if you're perceptive, you may notice that the parapet rods are all of different lengths. This is visually attractive, but offers an added surprise - the bridge plays music. Striking the rods with a stick plays a specially composed tune, made especially effective because the box girder acts as a resonant cavity.

It's a crying shame that the bridge has received so little attention (although it was shortlisted for a RIBA 350 Award in 2010). I think it's one of the most interesting footbridges to be built in the UK in the last few years, a delightful little haiku in Cor-Ten.

Bridges news roundup

2011-10-02T23:32:00.000+01:00

Web of Iron exhibition celebrates all chain bridges
The visitor centre at Union Chain Bridge (see previous post) now has an exhibition on the development of early iron chain bridges.

M20 footbridge given the all-clear to open
£8m cable-stayed bridge cleared for use despite "persistent rumours" of an "unexpected wobbling".

Plan for new bridge at Bradford-on-Avon is scrapped
End achieved to endless debate over a modern cable-stayed footbridge proposal.

£650,000 bridge is built ... for bats
I should link to The Sun more often.

West Country Bridges: 5. Royal Albert Bridge

2011-09-29T22:58:00.002+01:00

What is there that I can sensibly say about Isambard Kingdom Brunel's greatest bridge (pictured, above left)?

First, the facts. The bridge was opened in May 1859, four months before Brunel's death. The two main spans of 138.7m are achieved using giant lenticular trusses in wrought iron. The upper chord of the truss is a single tube, oval in cross-section, 5.1m wide and 3.7m high. The lower chord consists of wrought iron chains, with vertical members carrying the loads from the deck into both chords. It's a design with split personalities - as well as the idea of the lenticular truss, you can think of it as a bowstring arch bridge, or as a self-anchored suspension bridge in which the main cable forces are anchored into an overhead strut rather than into the deck.

In this respect, the design was a development of Brunel's 1852 bridge at Chepstow, where again a simplified suspension arrangement relies on tubular strut for its anchorage (although at Chepstow, the strut was circular). Another predecessor was Brunel's 1849 bowstring arch at Windsor.

The Royal Albert Bridge also owed more than a little debt to Brunel's great friend and rival Robert Stephenson. His High Level Bridge in Newcastle was also completed in 1849, and has a series of bowstring arches carrying the roadway, with the railway on a separate deck above the arches. The idea of superimposed systems may have influenced the Royal Albert Bridge, but another Stephenson design was even more relevant, the Britannia Bridge.

Opened in 1850, the two main spans at Britannia were very similar to Royal Albert, at 140m. The same method of erection, by floating out and lifting vertically, was also used on both bridges. The Britannia Bridge (along with a related structure at Conwy) had pioneered the use of riveted wrought iron box girders, although used in a beam arrangement rather than as struts as in the more complex Brunel design. Stephenson had even suggested the use of an oval box girder at Britannia, although William Fairbairn's preference for a rectangular section proved more appropriate.

Brunel's Royal Albert Bridge was a more sophisticated design all round, but not of a type which would see much further use. The first major Warren truss bridge had been built in 1852, and lattice trusses such as the Runcorn Railway Bridge were soon to come into favour. Truss bridges were simpler to assemble than box girder designs, and used significantly less material. Nonetheless, Brunel's lenticular truss certainly didn't stand alone, with several other examples built by von Pauli and Lohse in Germany, and by Lindenthal and the Berlin Iron Bridge Company in America.

None of this is to detract from the Royal Albert Bridge. It may have been a technological dead end, but it remains a remarkable design and a spectacular structure.

I particularly like the texture of the main arch girders, with the riveted plate form very visible. The evidence of handicraft is a welcome contrast to the more impersonal surfaces that modern welded construction produces.

Perhaps less appealing are features which I presume to have resulted from strengthening works over the years. Chief amongst these are the diagonal bracing members immediately below the suspension chain, which aren't visible on older photos, and detract from the clarity of the structural system.

Further information:

Google maps / Bing maps
Wikipedia
Structurae
Engineering Timelines
English Heritage
royalalbertbridge.co.uk
Royal Albert Bridge (Buxton-Smith, 2007, student paper)
British Railway Bridges (Walters, 1963)
British Railway Bridges and Viaducts (Smith, 1994)
Civil Engineering Heritage: Southern England (Otter, 1994)
Cornwall's Bridge and Viaduct Heritage (Kentley, 2005)
An Encyclopaedia of Britain's Bridges (McFetrich, 2010)

West Country Bridges: 4. Tamar Bridge

2011-09-27T20:39:00.000+01:00

It's not often that I feature long-span bridges on this blog. The scale and complexity of major bridge projects makes them less easy to encapsulate in a short text. Smaller structures are easier to do justice to. However, in this current series of posts, there are two more bridges that it would be remiss not to include. This post will cover the one on the right, in the picture above.

Opening in 1961, and spanning 335m, Tamar Bridge was the first of three major British suspension bridges to be completed within a few years of each other, its siblings being the Forth Road Bridge (1964, span 1006m), and the Severn Bridge (1966, span 988m). Its nearest significant predecessor was the 101m span Chelsea Bridge, completed in 1937, although the longest spanning suspension bridge in Britain at the time dated back nearly a century, the Clifton Suspension Bridge (1864, span 214m) (I'm not counting the 300m Widnes-Runcorn Transporter Bridge, which is a special case).

By the standards of what had been built in American and elsewhere, the Tamar Bridge was not a major structure. The design, by Mott, Hay and Anderson, was of the old-fashioned stiffened deck-truss type, still the legacy of the Tacoma Narrows failure from two decades before.

However, this conservatism was forced on the designers by the proximity of Brunel's Royal Albert Bridge. Tamar Bridge shared its design and year of opening with the Runcorn-Widnes Bridge, which also had a very similar main span of 330m. At Runcorn, a 314m span suspension bridge was rejected in favour of a steel truss arch design as a result of wind eddies generated by the nearby Runcorn Railway Bridge. At Tamar, the wind tunnel tests showed that a small change in level of the new road bridge would be enough to solve a similar problem.

The Tamar trusses are some 4.9m deep, with a span-to-depth ratio of 68, almost absurdly deep for a suspension bridge even at the time. As built, it had only vertical hangers, but when it was widened at the end of the 1990s, stay cables were added, creating a hybrid form. Unusually, the main suspension cables are locked-coil steel ropes rather than aerially spun cables, with 31 ropes bundled together in each cable.

The design of the widening, by Hyder, involved extending the bridge deck on new cantilevers, which carried traffic during the construction period. The original concrete deck was replaced by a lighter orthotropic steel plate deck, and traffic then returned to its original lanes. The cantilevers now carry local traffic on one side, and a footway / cycleway on the other. The overall result is not just that the bridge is stronger, but also more attractive, as the main trusses are to some extent shadowed by the deck cantilevers.
Further information:

Google maps / Bing maps
Wikipedia
Structurae
Engineering Timelines
Pathe film showing construction
Modern British Bridges (Henry & Jerome, 1965)
Civil Engineering Heritage: Southern England (Otter, 1994)
In the Wake of Tacoma: Suspension Bridges and the Quest for Aerodynamic Stability (Scott, 2001)
The Tamar Bridge (Brown, 2007, student report)
An Encyclopaedia of Britain's Bridges (McFetrich, 2010)

First Schlaich Bergermann bridge in Britain?

2011-09-25T23:12:00.000+01:00

Manchester City Football Club (MCFC) have recently submitted a planning application for a new sports training complex, across the road from their existing City of Manchester stadium. The scheme involves a dedicated mini-stadium, indoor and outdoor training pitches, and supporting buildings. It's probably the most ambitious football construction project in the UK at present.

The new facilities will be linked across a main road to the football stadium by a new landmark pedestrian bridge. The structural designer for the project generally is Capita Symonds, and their name is on the draft technical approval document for the bridge, but judging from the names on the planning drawings, I think this is actually a Schlaich Bergermann design. It looks like it could be their first bridge to be built in Britain, with their closest previous attempt failing to get off the ground.

The present design is for a 90m span tubular arch bridge, with two inclined arches. The arches have a common springing at one end, where the bridge deck diverges in a Y-shape, and twin springings at the opposite end, where there is only the single straight deck. The tubes therefore intersect in one place above the deck, giving a plan arrangement very like the Christian ichthys symbol. I wonder whether the football club's owners, the Abu Dhabi United Group, have spotted this.

The deck is a minimum 5m wide trapezoidal steel box girder with steel rib cantilevers supporting a concrete deck slab. The parapets are in stainless steel, with horizontal tensioned rods as the infill. The deck is suspended on spiral strand rope hangers, which also run between and stabilise the main arch members.

The asymmetry of the arrangement will lead to some asymmetry of loading on the arch, but I would guess not enough to be of any significance. More interestingly, the angle of the hangers will be asymmetrical, which should lead to an interesting visual effect, with the hangers shallower and hence "opening out" as you walk away from the main football stadium, rather than towards it.

As ever, click on any image for a full-size version. All images have been taken from the planning submission documents. The images on the Manchester City website give a wider impression of the context for the new footbridge.

West Country Bridges: 3. Halgavor Footbridge

2011-09-21T21:56:00.130+01:00

This little suspension footbridge at Halgavor, near Bodmin in Cornwall, was on my must-visit list.

It carries a footpath and bridleway 47m across the A30 highway, poking out shyly from between the trees on either side. Driving under it, you can see the main span but not the support towers, while from above, it is similarly difficult to find a viewpoint taking in the entire bridge. This sense of modesty is unusual for such an adventurous little structure.

Halgavor footbridge was designed by Wilkinson Eyre and Flint and Neill for the Highways Agency, opening in 2001, and even at first sight is an unusual structure for that body. At this span, some form of metal truss would have been a straightforward solution, and probably with lower initial cost than what was built.

It's a reasonably conventional suspension bridge, although the towers are tilted back from the span (see picture, click on any picture for the full size version), and the parapet posts arranged radially for visual effect. However, its dainty appearance hides its innovative nature.

The steel towers are the only part of the bridge likely to require substantial maintenance, in the form of repainting. The main suspension cables are in galvanised steel. The hanger cables, parapet posts, and parapet infill mesh are all in stainless steel, helping to minimise the need for future maintenance over the highway. The lower part of the parapets is in timber boarding, to meet bridleway requirements.

The deck is the feature that has got the bridge the most attention, being constructed largely out of glass-reinforced plastic (GRP). With the GRP resin formulated to protect against ultra-violet attack, it should therefore require little or no maintenance, minimising future disruption to the highway. It's paved in rubber blocks made from shredded, recycled rubber, which provide a happier surface for horses' hooves and also contribute to the structure's damping.

The upper-layer of the deck is a double-skinned sandwich plate, providing the necessary stiffness to resist out-of-plane pedestrian loading. Channel sections form the sides, and a series of diaphragms and a lower plate are assembled into a box-girder form. It was reportedly the first GRP bridge built in the UK by a publicly-funded body, and as such, considerable innovation had to go into its design and construction.

The difficulty with bridges like this is putting them in a context where the innovation becomes repeatable and more widely applicable. In the ten years since Halgavor Footbridge was opened, very few comparable structures have been built in the UK, and generally of much less aesthetic value. Most of the GRP and CFRP structural systems available are based around automated fabrication (such as pultruded sections). Elaborate lay-up and assembly appear less common, and such examples as I have seen are very ugly.

I'm reminded of the Lockmeadow Footbridge, by the same design team, another lightweight, aesthetically sensitive structure where the more innovative elements (an interlocking aluminium deck, and GRP parapet posts) have failed to see any wider adoption.

Visually, I think there is much to admire at Halgavor. The parapets are particularly good, especially with the combination of timber and stainless steel, but mainly for the attention paid to keeping it simple and transparent. The suspension arrangement is more attractive than the use of vertical hangers, at least in this setting.

There are peculiar arms which extend from the abutments to cradle the deck, and I struggled to work out what they were for. According to a technical paper about the bridge, they are there to soften the disjuncture in stiffness between the suspended deck and its connection with the abutments, which is fixed (thermal movement is addressed by vertical flexing of the lightly-arched deck). As in a stress-ribbon bridge, the bending moment at the support is otherwise too high for a slender deck such as this to accommodate.

Further information:

Google maps
Structurae
Flint and Neill
Wilkinson Eyre
New Materials for New Bridges: Halgavor Bridge, UK (Firth & Cooper, Structural Engineering International, 2002)
Application of Safety Factors in the Design of Halgavor Bridge (Cooper, 5th CoSACNet Workshop, 2002) (includes several images of fabrication and construction)
A Tale of Two Bridges: The Lockmeadow and Halgavor bridges (Firth, The Structural Engineer, 2002)
New Materials for Modern Footbridges (Firth, Footbridge 2002)
Bridges (Arcila, 2003)
Stress Ribbon and Cable-Supported Pedestrian Bridges (Strasky, 2005)
Cornwall's Bridge and Viaduct Heritage (Kentley, 2005)
Footbridges (Schlaich & Baus, 2008)
An Encyclopaedia of Britain's Bridges (McFetrich, 2010)

West Country Bridges: 2. Newquay Suspension Bridge

2011-09-20T22:55:00.012+01:00

I am an absolute sucker for these early-20th century suspension footbridges. A large number were designed and built by David Rowell & Co., with latticework towers and often unstiffened bridge decks suspended from wire ropes. Another prolific designer and builder was Louis Harper, who worked for James Abernethy as well as in his own right.

This particular example crosses from the Cornish mainland to Towan Island at Newquay, and is well known to locals and tourists, although seemingly not to the bridge community as it is not covered in any of the obvious books.

The excellent Harper Bridges website records that this bridge was reportedly commissioned by Victorian novelist Hal Caine to provide access to a summer house on the island. The bridge was originally similar in form to most of Louis Harper's suspension bridges of the periods, with lattice metalwork towers topped by pointed finials.

Another source reports that at one time there was a teashop on the island, with a toll of 2 old pennies charged to cross the bridge. The present house was built in the 1930s, and the bridge and island are both currently privately owned, although you could buy it for a mere £1.25m.

At some time, the latticework towers have been encased in concrete, presumably as a simple solution to a corrosion problem given the proximity to salts from the sea, which passes below the bridge.

It's an unusually spectacular location for such a bridge, by British standards, with most of the contemporary examples spanning more gently between riverbanks. As it's private, I wasn't able to gain access to the bridge itself, but hopefully the photos give a reasonably clear idea of the structure.

The bridge spans only about 30m, short by the standards of modern suspension bridges. I think it's a huge shame that the suspension form is rarely used for this sort of structure today (at least in the UK - there appear to be bucketloads of them in Japan), and would attribute some of that to the tyranny of codes of practice and methods of analysis. Bridges like the Newquay one are relics from an age where bridges were the products of craftsmen who learned what worked from experience as much as relying on their methods of calculation.

The equivalent firms to Rowell and Harper today, the specialist footbridge fabricators, produce in the main simple steel truss designs which are straightforward to analyse and efficient to erect. Little or no specialist knowledge is required. I wonder whether a place might ever arise again for a firm which would invest in R&D, develop its own system, use patent protection as a key source of income or monopoly, and help return us to structures which are lightweight and visually attractive.

Further information:

Google maps / Bing maps
Harper Bridges
Cornwall's Bridge and Viaduct Heritage (Kentley, 2005)
The Nineteenth Century Footbridges of Harpers of Aberdeen (Harper & Day, Industrial Archaeology Review, 2010)

West Country Bridges: 1. Postbridge

2011-09-19T19:47:00.001+01:00

Ok, time for a few bridges from the south-west of England, all in the counties of Devon or Cornwall, or in some cases both.

The first, Postbridge, is a clapper bridge spanning the East Dart near Princetown. It's believed to date to the 13th century, and is a Grade II* Listed Building and Scheduled Ancient Monument.

The granite slabs each span about 3m, and are reported to weigh up to 8 tons each.

The bridge's proximity to the roadway means this is one of the most visited of Britain's clapper bridges, as can be seen in the photographs. Tourists or not, it retains a timeless quality which belies the fact that it has been repaired and rebuilt on more than one occasion, most recently circa 1970, when the slabs were bedded on a resin mortar to eliminate movement.

I'd have preferred to have seen the bridge with fewer visitors, it seems almost uncouth for something so primitive to be so well-used.

As a designer, I wonder why it is acceptable to have no handrail on an ancient monument but one would be demanded on an equivalent bridge built today. Surely the risk of falling off is the same in either case? Does protection of heritage have more importance than the risk of injury, or should we simply recognise that the risk of injury is so low as to be an irrelevance, whether many centuries ago or today?

Further information:

Google maps / Bing maps
Structurae
English Heritage
Legendary Dartmoor
Virtually Dartmoor
British Bridges (Johnson & Scott-Giles, 1933)
Bridges of Britain (Wright, 1974)
Civil Engineering Heritage: Southern England (Otter, 1994)
An Encyclopaedia of Britain's Bridges (McFetrich, 2010)

Concepts published for St Botolph's Footbridge, Boston

2011-09-18T23:18:00.072+01:00

That's Boston, Lincolnshire, not Boston, Massachusetts.

Lincolnshire County Council is proposing to demolish and replace the existing St Botolph's Bridge, which spans the River Witham in Boston. It's a remarkably ugly metal girder bridge (pictured, click on any image for the full-size version), which isn't suitable for use by the mobility-impaired and was found to have structural defects earlier this year. They have a £600k budget and a yearning for something better.

Three design concepts have been released for public consultation, all from local architect Neil Dowlman Architecture (there's no mention of an engineer). All three options are supposed to improve accessibility, reduce maintenance, enhance the environment, and provide improved views of the river and the nearby St Botolph's Church.

The first option is for a so-called bowstring arch, with twin tubular steel arches inclined against each other. I say "so-called", because the deck and arch are only connected in the visualisation by a transverse member which would seem insufficient for a proper connection, and hence the bowstring behaviour will be compromised. This is straightforward to amend, however.

It spans about 35m, with 15m ramps either end, and varies in width from 3m to 4m. The available finance therefore works out at about £2.6k per square metre. The concept has structural glass balustrades with concealed handrail lighting, which together are likely to be a costly component, and don't seem to fit well with the aspiration for reduced maintenance problems.

I don't know the town so don't know how well this design fits within the landscape, but I would have thought a lower-profile solution might be more appropriate, if opening up the views is of primary interest.

The second option is described as the "traditional" design, with a deck-type bridge resting on gently curved lattice beams, with guardrail-style parapets. Lighting is from antique-style lamp-posts. Longer ramps are required because the bridge must sit higher above the river level.

The final option is derivative of the first, with "bowstring trusses" of lower height. These are in a Vierendeel style. The relatively low angle of the upper chord at the ends of the bridge will make structural design difficult, but I would see the main objection to this option as being the fact that the lower-height truss interrupts views off the bridge.

To me, there are two obvious options which seem to have been neglected. The first is the traditional half-through girder design, with twin edge girders cradling the bridge deck, and topped by handrails to provide transparency of views off the bridge. At a 35m span, this should just about be achievable without requiring the girder to extend all the way up to handrail height. It would offer better views than the "bowstring" options, and shorter ramps than the "traditional" alternative.

A second option would be a spine-girder solution, with a single central beam raised above deck level and doubling to provide seating. The views would be the most transparent of any solution, although the depth of girder required at 35m would mean higher ramps than some alternatives (albeit still much less than shown for the "traditional" design).

I always find it irritating when a public consultation presents a false or partial choice, but it remains an early stage for this project, and in my own work I have been amazed how different the final design sometimes turns out from the early concepts presented. In this instance, a quick look on Google Street View and at pictures of the nearby church suggests to me that prominence is best avoided.

Paolo Soleri's Bridges

2011-09-15T21:22:00.075+01:00

Tallbridgeguy mentioned this before me, but I had planned to feature it here anyway.

ArchDaily has a very interesting post with text and images of the American architect Paolo Soleri's bridge designs. Only one of his bridges has ever been built, a horrible footbridge at Scottsdale, and judging from the many other examples showcased, that may be no bad thing.

Soleri is a classic example of an architect whose sympathy for structure is superficial at best, with even his best known bridge design, a proposal featured in Elizabeth Mock's seminal The Architecture of Bridges, showing a thorough contempt for the imperatives of construction. Pictured above, this design was criticised by the Italian engineer Pier Luigi Nervi for "start[ing] from a purely formal conception ... with the sub-conscious thought that the 'calculator' will manage to make it stand and the constructor will be able to build it."

Sometimes, this lack of embedment within a discipline can result in a design which shatters hidebound preconception and reminds us quite how trapped we often are within the habits of tradition. Many of Soleri's designs look lovely on paper, science fiction fantasies of what a bridge might be unconstrained by gravity or cost.

I'm particularly struck by his Ponte Lussemburgo proposal shown above, described as a "double cantilever inter-related three-dimensional structural members in ferro-cemento" (click on any image for a full-size version). Its sinewy curves are artistic rather than rational, but there's a family resemblance to Sergio Musmeci's astonishing Basento Viaduct.

I'm reminded that there are many histories of structural engineering yet to be written. Those few that do exist are partial and often hamstrung by linguistic limitations: the likes of Musmeci are rarely featured in books on bridge engineering. Beyond the bridge world and considering wider structural engineering, the English-speaking world often seems largely ignorant and unappreciative of great designers like Heinz Hossdorf, Ulrich Müther or Eladio Dieste.

If a history of the unknown would be welcome, a history of the unbuilt and unbuildable would be equally so, and Soleri's bridges would certainly merit inclusion.

Bridges shortlisted for IStructE awards

2011-09-14T20:58:00.000+01:00

This year's Institution of Structural Engineers awards feature a number of bridge schemes.

The pedestrian bridges shortlist has:

The Helix, Singapore (Arup / The Cox Group / Architects 61)
Media City Footbridge, Manchester (Gifford / Wilkinson Eyre)
Redhayes Bridge, Exeter (Parsons Brinckerhoff / Design Engine)
Bridge of Dreams, Princeton (Fast + Epp)

I will reserve comment, due to lack of time, but feel free to click the comment button and add your own!

The reconstruction of the Mizen Head Footbridge is shortlisted in the Heritage category, while the Sheikh Zayed Bridge is shortlisted under Transportation Structures.

The winners will be announced on the 8th November.

Bridges news roundup: Mega Edition

2011-09-13T12:57:00.000+01:00

It's been some time since I've done a roundup of bridge-related news, so there is quite a bit to cover this time ...

Italy's bridges weighed down by locks of love
I recently wrote about the tradition of adorning Wrocław's Tumski Bridge with padlocks as a symbol of marital or romantic commitment. It appears the Venetian authorities are less than keen on seeing the same tradition applied to the Rialto Bridge. I didn't spot any locks when I visited it, but perhaps this was simply because the authorities were quick on the draw with their boltcutters. It's a shame they are less effective at removing graffiti.

Daredevil takes on Gateshead Millennium Bridge stunt
As this video shows, it's not quite as crazy as the original article makes it sound.

Gateshead Millennium Bridge celebrates 10th anniversary
Designer Jim Eyre interviewed.

Barnard Castle Bridge moves step closer
Plans are afoot for a £1.3m, 265m long pedestrian suspension bridge. That strikes me as too little money for that much bridge, unless it really is done on the cheap, forestry-style.

New Tempe Town Lake pedestrian bridge draws attention
As well it should. See this site for more construction images, or play spot the difference.

Diamond idea for bridge
The suggestion is that the proposed New River Wear Crossing in Sunderland (pictured, right) should be named the Diamond Jubilee Bridge as part of a wheeze to help persuade cash out of the central government in order to support what is undoubtedly a local council vanity project. They are not the first to have this idea - you heard it here first.

New Wear Crossing funding bid
Meanwhile, Sunderland have submitted their revised bid for central government cash for the wider highway scheme of which the bridge is only the most prominent part. The bid cuts roughly £15m off the previous estimated £133m scheme cost. Of the new £117.6m figure, roughly £72m is for the bridge itself, with the rest for highways, land and utilities.

An examination of the documents reveals that considerable "value engineering" has taken place (cost-cutting, in normal parlance). The twisty masts of the bridge have been reduced in height, bespoke parapets and road lighting have been replaced with their bog-standard equivalents, and structural finishes have been reduced in quality. An alternative scheme with a conventional bridge is estimated at £109m, although much of that is due to additional design and land purchase work only necessitated by the fact that Sunderland have already spent large sums on the landmark bridge option. The difference between the landmark and alternative schemes is therefore a mere £8.6m, which is frankly almost impossible to believe. Sunderland have also made a commendable effort to calculate the regeneration and employment benefits of the landmark option, which they put at £33m.

Peace Bridge defenders say Toronto crossing not the same
Calatrava's CAN$25m footbridge in Calgary (the subject of many previous posts on this blog) is compared to the CAN$8m Puente de Lux in Toronto (see here). Both are trusses with curved web members, but the similarity ends there. The Toronto span is essentially a Warren truss with pretensions, while the Calatravan helical truss bridge is a more complex beast. And one is yellow and the other one red. Quite, quite different.

Is it all over for £6 million bridge?

Answer: it was probably all over before it ever started. This footbridge in Gainsborough was an ambitious landmark structure (pictured right, and see my previous post for full details) which always seemed at risk of cost escalation, and perhaps over-ambitious for a town which started with no funding in place and remains in the same position. What's odd is that the council granted a local body (now disbanded) £12,000 to develop the initial design but has, apparently, never had any real intention of taking the scheme further. If so, why waste the development cash?

City river footbridge to be lifted into place after year of delays
Hull's £7.5m pedestrian swing bridge (note it was only £6.5m when I last reported, in June) was finally ready for installation after considerable delays due to the local council drip-feeding the finance. It's unclear whether the revolving restaurant will have a tenant yet, or whether lack of cross-river development will make this something of a white elephant.

London Bridges: 16. Royal Victoria Dock Bridge

2011-09-11T21:39:00.000+01:00

The last in my current set of bridges from London's Docklands is further east than the others, at Royal Victoria Dock. In 1995, the London Docklands Development Corporation held a contest to design a bridge spanning this huge, if now little used, dock. I featured some of entries here previously.

The winning design was a spectacular 127.5 span "inverted Fink truss" bridge, designed by Techniker with Lifschutz Davidson, completed in 1998 at a cost of £5m. It was originally intended as a transporter bridge, with a gondola active at low level. The bridge has, however, never seen enough use to justify installation of the gondola. The adjacent ExCeL exhibition centre is one of the venues for the London 2012 Olympic Games, which may see the bridge getting much greater use, at least for a short while.

There are very few bridges of the "inverted Fink truss" type around. The only other examples which come to mind are the Forthside Footbridge, at Stirling, and the Passerelle La Défense, in Paris, although there have been unbuilt proposals.

A key challenge in designing the bridge was the need to maintain a 15m clearance to the dock, allowing tall-masted ships to pass below. This was imposed by the client upon competitors, and seems to me to have been what the kidz would now call an Epic Fail. In the absence of the gondola, to cross the bridge you have to ascend and descend multiple flights of stairs, or endure the mangy lifts. It's not even as if the view from the bridge is sufficiently exciting to justify the exertion. As the dock is hardly ever used by tall ships, I would have thought that a low-level structure with an opening element would have been a better choice.

If the gondola is ever installed, I think that opinion would be reversed, and I think that seeing the bridge operate as a modern-version of a Ferdinand Arnodin-style transporter bridge would be quite splendid.

A short distance to the north, an elevated walkway structure connects ExCeL to a Docklands Light Railway station, but the possibility of connecting this directly to the bridge via a ramp has so far been missed.

Viewed in elevation (as in the first photo above), the stair and lift towers, which are heavily metal clad, have a monolithic, blocky character totally out of keeping with the rest of the bridge. However, the bridge is generally viewed from a much more acute angle, and the towers are less problematic from most perspectives.

The bridge itself is a very strange beast, something like an elephant as it might be sculpted by Alberto Giacometti. The deck is just that, a promenade-style walkway translated vertically, and set upon comically spindly stilts. This is not entirely a bad thing, it emphasises the sense of the bridge as a platform rather than as a pathway.

The cable and mast arrangement above the deck has a certain logic relating to the diminishing forces to be carried by successive cantilevers away from the supports, an approach repeated by the other inverted Fink truss bridges and which here appears justified by the visual scale of the bridge in relation to the dock sides. Single masts on the bridge centreline give a clarity to the composition which isn't harmed at all by the consequent need to have twin pairs of cables connecting the masts to both sides of the deck. The mast and cable arrays form a set of overlapping tetrahedra, with the variation in mast height eliminating any geometric clash of cables (except for the centre bay, where a link arrangement has to be used to solve this problem, see the photo).

I find the relationship of the above-deck masts to the below-deck support legs to be less admirable - it would have been great to have seen single legs relying only on cables for lateral stability. The sense of incongruity is enhanced by the adoption of a cigar-shape for both the legs and the masts, although this makes structural sense.

The bridge deck has a dual personality - Iroko timber decking and handrails give the feel of a promenade from above, while from below, it has the qualities of a metallic millipede, or perhaps the snout of a sawfish. Structurally, there is a steel box-section spine beam, with the deck and balustrades supported from cantilevered fins. The box incorporates a slotted element in its soffit which currently carries a maintenance gantry and which would carry the proposed gondola. The designers, Techniker, make great play of the fact that the main deck elements are not bolted or welded together, but pegged together and prestressed, which is a highly unusual choice for a structure of this type and scale.

The balustrades are in perforated plate, which gives a greater feeling of security at this height than would a lighter-weight wire, rail or mesh solution, and also enhances aeroydynamic stability. As with most elements of the bridge, they seem to be lasting well.

The bridge deck at first seems very slender, although at deck level, it is apparent that this is because most of the spine beam box girder has been allowed to protrude upwards through the decking.

The steel box is profiled to carry the bending moment between points of support, in a similar manner to Castleford Footbridge. However, at Royal Victoria Dock, the opportunity to create areas of seating was missed. The boxes resemble upturned boat hulls, part of a nautical theme that persists throughout the structure (with its spars, cables, and bowsprits), but I think seats would have been preferable.

The Royal Victoria Dock Bridge is described by its designer, Matthew Wells, as having "reacted strongly against the prevailing fashion for iconic bridge structures presented as catalysts for urban renewal" (in Engineers: A History of Engineering and Structural Design (2010)). While there has been very little urban renewal at the site (the ExCeL centre is pretty much it), it's hard to see a bridge of this scale, idiosynractic choice of form, and modernist starkness as anything other than iconic.

I'll finish by noting that there were plans to supplement this bridge with another further along the dock. In early 2010, a competition was announced, subsequently won by Ian Ritchie Architects. Ritchie came up with a number of suggestions, including a floating bridge, but a unique swing bridge solution, the "water boatman" was the favourite until Olympics funding cutbacks killed the entire scheme. It only emphasises what a mistake it was to require the 1998 structure to be so high in the air - while it resulted in a very heroic, spectacular design, it provides far from the ideal pedestrian experience.

Further information:

Google maps / Bing maps
Structurae
Wikipedia
LUSAS
LDDC History
http://www.independent.co.uk/arts-entertainment/architecture-a-bridge-not-far-enough-1189058.html
The Architecture of Bridge Design (Bennett, 1997)
30 Bridges (Wells, 2002)
Bridge Builders (Pearce & Jobson, 2002)
Bridges (Arcila, 2003)
Footbridges (Schlaich & Baus, 2008)
An Encyclopaedia of Britain's Bridges (McFetrich, 2010)
The World of Footbridges (Idelberger, 2011)

London Bridges: 15. Great Wharf Road Bridge

2011-09-06T23:21:00.000+01:00

There have been some pretty weird opening bridges in my last few posts. The Limekiln Dock bridge is perhaps unique amongst swing bridge designs, with its rotating pylon and strutted, offset, asymmetric main span. The same is true of the upper-level Bellmouth Passage footbridges with their lack of any counter-balance back-span. The Bellmouth Passage road bridges are bascule bridges with ring girder supports rotating about a virtual pivot, and again probably unique.

You don't have to walk far from these (all in the Canary Wharf area in London Docklands) to find yet another unusual opening bridge, at Great Wharf Road.

The structure is a 65m span highway bridge, opening like a bascule bridge, i.e. hinged at one end while the other end rises into the air. Most bascule bridges have an unlimited air draft i.e. once raised, vessels of any height can pass through, but that is not the case here. Instead, the bridge lifts only 18m at its tip, which is raised directly by an enormous hydraulic ram. In most bascule bridges, the lifting equipment is positioned near the pivot end, and a substantial counterweight is required so that the ram carries only a small load.

Here, the span is too great for that type of bascule bridge, and there is no space for the counterweights that would be needed for a double-leaf bascule (the obvious solution, along with a lifting bridge).

The bridge was designed by Gifford with Wilkinson Eyre. The exemplar mechanical design was by Atkins Bennett, and detailed design by Davy Markham. The structure was fabricated by Hollandia. The hydraulic piston which opens it supports a load of up to 660 tonnes. There are images of the bridge opening at the Atkins Bennett website which should make the mode of operation clear.

It's notable that the bridge as-built is a value-engineered version of the original design, which is shown in the image on the right (click to see a larger version). The concept design covered the two footways in glass enclosures. The only element of these to survive is a peculiar semi-transparent panel which fills the space between the arch and the deck - it seems somewhat redundant in the current arrangement.

The Wilkinson Eyre influence remains apparent in the detailing - I like the way the hangers interface with the arch ribs, for example.

The link below to Bing maps shows the bridge how it was - spanning the water of West India Dock. Use by vessels requiring the bridge to open was rare, and I believe it was designed only to open 12 times a year.

The link to Google maps, and my photos, show the bridge's current situation. Most of the dock has been turned into a giant cofferdam for the construction of the Crossrail Canary Wharf station. The cofferdam is some 256m long, 45m wide, and up to 28m deep. Parts of the Great Wharf Road Bridge deck had to be temporarily cut out to allow the dam wall to be installed, and the bridge now spans one of the largest construction sites in London.

Once the station works are complete, the bridge will span above an area of landscaping combined with much reduced waterways. I am unsure whether it will still be required to open.
Further information:

London Bridges: 14. Bellmouth Passage Bascule Footbridge

2011-09-02T21:34:00.050+01:00

The opening highway and pedestrian bridges covered in the last two posts span the Bellmouth Passage at a high level, providing connectivity to vehicles and people at what is the normal ground level for the Canary Wharf site. However, there are promenade walkways alongside the Passage at its lower level, which until very recently were not connected.

A new opening footbridge has been introduced to address this, midway between the twin highway bridges.

Somewhat unfortunately, the bridge has been installed above the promenade level, requiring the use of steps or very short lifts to reach it. What little I initially found online suggested that this is so that the bridge's opening machinery could be located above ground level. The planning application appears to confirm this: the promenade is a slab structure, and perhaps it was judged to be too expensive to reconstruct it locally to install a lower-level machine room.

There is also a constraint imposed by British Waterways, who required even the closed deck to provide 3m clearance to the waterway, which is 1.8m above promenade level. Click on the image above right for an extract from the planning drawings illustrating the arrangement.

The span is a single-leaf bascule bridge, with the hinge on the west side well disguised within the floor panels (see the image on the left). The bridge deck consists of a steel box girder supporting aluminium deck planks and stainless steel balustrades.

The bridge abutments are clad in red and grey, providing a welcome splash of colour amongst the generally monochrom surroundings. It's a quintessentially modern, technological bridge, which in this colour scheme wouldn't look out of place at the McLaren HQ in Woking, but offers anonymity rather than being particularly high-quality.

Perhaps there is more boat traffic through here than I suspect, but I find the decision to raise this bridge above the surrounding promenade to be a real disappointment, whatever British Waterways may have said. It's a two-fingered salute to the less able-bodied and visually it detracts from the waterfront space.

I have nothing else to report - I don't know for sure who designed or built the bridge (Adamson Associates are the architects responsible for the planning submission, and Atkins are credited with the development of the opening mechanism proposals), or when precisely it was built, and neither Google nor Bing show it on their current satellite imagery. Please post in the comments if you know anything more!

London Bridges: 13. Bellmouth Passage Swing Footbridges

2011-09-01T21:44:00.000+01:00

The two opening highway bridges featured in my last post are supplemented by two opening pedestrian bridges. These are covered walkways providing links across the Bellmouth Passage between office and retail facilities.

Unlike the road bridges, which were an unusual bascule variant, the twin footbridges are swing bridges, although again they are highly unconventional in their form.

The spans were designed by Patel Taylor and Techniker, who won a contest against five other design teams (two of the unsuccessful proposals are available online here and here, and a third is pictured in Mike Schlaich's book Footbridges).

The design is strikingly simple yet highly audacious. The bridge structures consists of a cellular box beam supporting a glazed superstructure, and supported (when open) at only one end, on a huge pivot.

In a conventional swing bridge, there is at least a short back span behind the pivot, to counter-balance the main span. At Bellmouth, the impression is given of a walkway structure held up by magical sky-hooks. In reality, the counterweight is contained within the part of the structure above the pivot, something which makes my belly feel queasy, and which could only ever work for such short, light spans as these.

Further information:

London Bridges: 12. Bellmouth Passage Road Bridges

2011-08-31T21:32:00.000+01:00

Bellmouth Passage connects two docks together near the east end of Canary Wharf. Within the space of about 100m, there are no less than five opening bridges.

The first two were designed by Wilkinson Eyre with NRM Bobrowski, and each carry highway traffic above the waterway. The Passage isn't used much by waterborne vessels (especially right now, while West India Dock is occupied by the gargantuan construction site for a CrossRail station), but opening bridges are necessary for when waterway traffic returns.

The bridge pictured is the northern of the two identical spans, and is of an unusual, if not unique, design.

It operates a little like a Scherzer rolling lift bridge, which is a bascule bridge which rolls back onto a curved girder, with a motion like a rocking chair. In the Scherzer design, the centre of rotation moves horizontally, whereas at Bellmouth Passage, it stays in one place. The rolling girder sits on support wheels, and a rack-and-pinion motor drives the bridge.

A more conventional bascule bridge wasn't adopted because there was no space for the conventional counterweight, with the client having specified that pedestrian access had to be maintained at dockside level. The brief also requested that there would be no visible structure above highway level. The chosen design solves the problem by positioning the bridge's pivot point midway between highway and lower footway, allowing the bridge to rotate about a "virtual fulcrum". The counterweight is incorporated within the elevation of the ring girder, as can be seen in the photograph to the left.

The only similar design I've ever seen was one of the losing proposals for the Foryd Harbour bridge design competition.

The bridge has two steel box girders supporting the deck, which are continuous with the ring girders. The highway deck is an orthotropically stiffened steel plate with a thin asphalt layer.

One feature of minor technical interest is that trief kerbs are deemed sufficient to keep vehicles on the road, allowing the use of lightweight mesh pedestrian parapets and timber footways. Unsurprisingly, this has led to seepage staining below, likely to be followed by paint loss and corrosion if road salts are being used on the highway.

This is not a beautiful bridge, but it is an ingenious one, and the ring girder has an obvious appeal. It may have visually more successful if it could have been a full ring, rather than having the top truncated, but the experience of being able to walk through it is unique, and must be doubly so when the bridge actually operates.

Further information:

Google maps / Bing maps
Structurae
Conceptual Design of Moving Footbridges, Footbridge 2008 (Cutlack, 2008)

London Bridges: 11. Limekiln Dock Footbridge

2011-08-30T21:42:00.000+01:00

Okay, my summer holidays are now out of the way, so hopefully I can return to something like normal service.

First up, I've got a batch of bridges in London's Docklands that I visited earlier this year. These are not all marvels of the bridge design world, by any measure, and that's doubly true of this first structure.

The Limekiln Dock bridge spans what was once a busy inlet from the River Thames, connecting riverside footpaths. When the Docklands was re-developed, this area was re-populated with housing, and although there were once mooring rights along the Dock, I'm unclear whether these still exist. They certainly must have done in 1996, when the footbridge was completed, as it is a swing bridge.

The bridge, designed by YRM and Anthony Hunt Associates, spans 34m. It was built by Littlehampton Welding, and is an asymmetric cable-stay bridge in design, with the main span balanced by a large counterweight slung off the back of the mast. The entire assemblage pivots to open, requiring a large space on the quayside to be reserved for the counterweight and its support arms, so they can swing sideways without any risk of an accident.

In the picture, you can see the arms supporting the counterweight, as well as two arms which support the deck, which is S-shaped in plan (the Bing maps link below gives the best general appreciation of the bridge layout - rotate the birdseye view to get an idea of the tidal range). There's the idea of an elegant bridge there, but the support arms and stiffness make it more like a hunchback on crutches.

Indeed, I've seldom seen such a promising geometry ruined by such dismal detailing. There's almost nothing about the bridge which works well. The counterweight is clunky, and the loss of dockside space that results is criminal; the mast resembles a leaden drinking straw; an unfortunate fender arrangement below part of the deck detracts from what little style its flat-faced deck girder might ever have possessed; and it's all in a shade of grey which would give a pessimistic air even to an industrial estate, let alone blemishing the riverside next to some of the most expensive real estate in London.

Luckily, some of the other bridges I visited were a little better.

Further information:

Outcry over plan to rebuild the Ponte dell'Accademia, Venice

2011-08-26T20:30:00.002+01:00

A repeat of the battle between city authorities and traditionalists over Calatrava's bridge in Venice may be in the offing. Proposals have been announced to replace the Ponte dell'Accademia, which spans the southern end of Venice's Grand Canal.

I featured the bridge here last year. It's a steel arch bridge built in 1986, clad in timber to resemble the previous structure, Eugenio Miozzi's 1933 bridge. As I reported then, plans have been brewing for some time to improve disabled access over the structure which, like many Venetian spans, has steep steps difficult for many users to negotiate.

The latest proposal (pictured), from Bolognese architects Schiavina, is for a complete reconstruction. The new bridge would cost about £5m, and depending on which website you read, would be built either in glass, steel and stone, or in glass, steel and timber.

In support of the plans, the city council claim that the cost of maintaining the existing bridge is exorbitant, and therefore reconstruction combines the ambitions of reducing ongoing cost and providing access for all. A recent refurbishment cost about £220k, and the authorities consider the future costs to be unsustainable.

Preservationists are up in arms, with the president of a Venice heritage group crying "The bridge has a certain dignity. Why don't we just restore it?" At present, there's no final commitment to build the new design, which has been considered by the local authorities and sent to the heritage ministry in Rome for approval. Protesters are however probably mindful of the precedent set by the construction of Calatrava's Ponte della Costituzione, where concerns over its contemporary design were ignored (in my view, probably rightly, as it hugely improves accessibility in an area where many visitors first encounter the city).

It's unclear how the work will be funded, with Venice notoriously unwilling to dig into its own coffers to maintain the historically valuable fabric of the city (as seen here). One report has multi-millionaire Renzo Rossi covering the costs.

I don't know whether replacement is the right solution. As an engineer, the question must mainly come down to the sustainability of bridge maintenance: is it really in such a bad condition that it is too expensive to look after? It did look a little on the shoddy side when I visited, but so do many bridges, and I suspect the cost of maintenance is being exaggerated.

Venice argues that its 1986 reconstruction means it is no longer a historic artefact and therefore not deserving of heritage protection. I don't buy that at all. A considerable effort was made to preserve the general appearance of Miozzi's bridge when it was rebuilt - it maintains a continuity of appearance which should not lightly be set aside.

The bridge's context is also highly significant. While I'm no fan of attempting to preserve the environment in aspic, there are few places where the cityscape is of such historic (and economic) importance as in Venice. The bridge is a key gateway to the Grand Canal, and in a place like this there should be a very good reason indeed for changing the bridge's appearance so much.

It is also worth considering the technical difficulties that imperil every bridge in Venice, particularly the inability of the ground to support large foundation loads. The first bridge at this site was a simple metal truss, imparting only vertical load. Miozzi's wooden bridge was relatively lightweight, but at 48m span even that required a large number of both concrete and screwed timber piles. The current bridge is heavier, but a new steel and stone bridge will be heavier still. If the Schiavina proposal proceeds, expect a lengthy political battle followed by difficulties with cost escalation (it is far from apparent whether an engineer is yet involved).

Finally, I have to ask why only a single architectural firm has presented a design for this site. Schiavina are not noted as bridge designers, but if the case for replacement is ever proven, then surely a site such as this merits the consideration of design proposals from competing designers?

We interrupt this usual service

2011-08-20T11:17:00.000+01:00

Ok, I've been away, and it will take some to recover, catch up with work, and get back to posting.

Coming up when I get time:

Reports on five or six more modern bridges from London's Docklands area
Three or four bridges in Devon and Cornwall
A review of Peter Lewis's book "Disaster on the Dee: Robert Stephenson's Nemesis of 1847"
The bridges of two Spanish design firms, which were shown at Footbridge 2011
A final batch of Where are they now? updates

Where are they now? Part 3

2011-08-14T20:23:00.095+01:00

Here's another batch of bridges which I featured on this blog during 2009, and have barely mentioned since. What has happened to them? How many have survived the great black hole of indifference?

North Coast Harbor Bridge

In September 2009, I posted details of six alternative options for an opening footbridge in Cleveland, USA, designed by Miguel Rosales. Judging from a recent news story, the US$5.5m twin-bascule drawbridge option got the nod, and is due to be built starting in 2012. Aviation restrictions seem to have ruled out the city's preferred single-bascule option.

Sheffield Parkway

I revealed proposals from Scott Wilson for a new footbridge over the A630 Sheffield Parkway in October 2009 (pictured). This was a much cut-down design which had replaced Tim Nørlund and Ramboll's previous RIBA-competition winning entry, ditched due to lack of budget. I've tried to find out whether the bridge is still going ahead, but without any luck.

Copenhagen Harbour Bridge

October 2009 also saw the announcement of a winning design for a new opening footbridge in Copenhagen. The winner, from Studio Bednarski and Flint and Neill, is an unusual retractable bridge. The project looked to be well organised and well funded, but I haven't found any further information on progress. Does anyone know whether design is complete, or a contractor appointed?

Johnson Street Bridge, Victoria

I reported several times on the battle between historic bridge preservationists in Victoria, Canada, and their local council, who appeared determine to replace a rare heel-trunnion bascule bridge with a new structure designed by Wilkinson Eyre (pictured). The story rumbled on into 2010, leading up to a town referendum in November 2010 on whether to borrow the money required to build a new bridge. I didn't keep up with the news, and didn't report the referendum result: the council won by a significant margin. In January 2011, geotechnical investigations for the replacement bridge commenced. In March, defects found in a structural inspection led to the closure of the existing rail span. It is due to be demolished next year.

Preliminary design of the new bridge is currently underway, and due to be complete in Autumn this year. The overall project completion date is targeted as March 2016. The new bridge will be a highly impressive structure, and definitely one to watch.

The heritage campaigners have shifted their focus to arguing for retention of a rail route on the new bridge.

Galp Energia Bridge

I reported on the winner of a contest to design a new foot and cycle bridge in Lisbon (pictured). This was essentially a vanity competition, run to support a design biennale, with an attractive prize fund but no firm plans to actually build anthing. Unsurprisingly, I've not found any sign that the design went any further.

Okay, that will do for now. I will do a final batch of catch-ups from 2009 in a couple of weeks time.

Wrocław's Bridges: 16. Pipeline Bridge

2011-08-11T20:18:00.032+01:00

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:

Wrocław's Bridges: 15. Zwierzyniecka Footbridge

2011-08-10T20:17:00.045+01:00

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

2011-08-09T22:16:00.020+01:00

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

2011-08-08T21:09:00.053+01:00

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

2011-08-07T19:29:00.064+01:00

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

2011-08-04T22:27:00.064+01:00

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

2011-08-03T20:26:00.028+01:00

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:

Wrocław's Bridges: 9. Słodowa Bridge

2011-08-02T21:25:00.022+01:00

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:

Wrocław's Bridges: 8. Mill Bridges

2011-08-01T21:21:00.039+01:00

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: 7. Sand Bridge

2011-07-31T23:30:00.036+01:00

Most Piaskowy connects the city centre of Wrocław to Sand Island.

The present bridge replaced a timber span in 1861, and is of a broadly similar type to that which could have been built in timber. It was designed by Ernst Uber.

The bridge spans approximately 30m, and is in the form of two riveted steel lattice trusses, supporting a tramway and highway deck between them. Footways are cantilevered to the outer sides of the trusses.

The current, rather bold, paint scheme was applied in 2008 - before that, the bridge was brown in colour. I like it - it really draws attention to what would otherwise be a rather drab structure.

In common with other lattice trusses using steel angle sections in the web, an interesting pattern of light and shade is generated, varying depending on the time of day. This is more marked on bridges with a denser lattice, however.

I think the balustrades are visually at odds with the main girders, the little mini-lattice at their base notwithstanding, and it's a shame that a modern fairing has been added to the outer edge, which really looks out of place.

Further information:

Google maps
Structurae
Wikipedia (Polish)
The best known bridges in Wrocław
Wratislavaea Amici (includes historic photos of the present and previous bridges)
Wrocław Mosty - Bridges - Brücke, Wiesław Jurewicz (undated book, ISBN 978-83-926759-5-2)

Wrocław's Bridges: 6. Tumski Bridge

2011-07-28T22:32:00.071+01:00

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

2011-07-27T22:26:00.002+01:00

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

2011-07-26T22:00:00.003+01:00

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

2011-07-25T20:47:00.003+01:00

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

2011-07-24T21:36:00.001+01:00

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 2010.

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

2011-07-21T22:46:00.048+01:00

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)