28 April 2017

Folly's end

So ... it was the Pontist wot won it*. Just a mere 5 days after I extensively documented the Garden Bridge's multitude of failings, London's Mayor Sadiq Khan has pulled the plug on his financial support for the scheme, almost certainly killing the project.
It's great that someone finally grew some balls and did what was necessary, but it's a scandal that it took so long and that £46m of public money had to be wasted first.

The Garden Bridge Trust has said little in response, but without government support, I anticipate that further private funders will withdraw their commitments, and the Trust will rapidly have to declare a halt to its activities in order to be able to meet its existing obligations to creditors. Without the mayor's financial guarantees, the Trust cannot start work on site as it cannot discharge a key planning condition.

Opinion on Twitter seems split about 90% against the bridge, and 10% in favour, with most celebrating the demise of this ignominious project (I guess not all my readers will have spotted that the Pontist is on Twitter now as well).

The death blow to the project came with Margaret Hodge's damning report released three weeks ago, but much of what Hodge said was only possible because of the investigations by Will Hurst at the Architects' Journal, who deserves some kind of award for his persistence in uncovering many of the saga's most sordid details.

There was an interview with Hurst on LBC Radio today, and students of this story should definitely listen to the interview and read the LBC's thorough report, both of which give a very clear idea of quite why the whole Garden Bridge stinks so highly.

The bridge's "demented enemies" (to use Boris Johnson's typically colourful phrase) will now turn their attention to seeing whether those responsible for this colossal failure can be punished or at least humiliated. Some are calling for public funds to be repaid, but there is no chance whatsoever of that happening.

So far as I can see, the project's key protagonists (Johnson, Lumley, Heatherwick) have yet to say their piece, but I don't think they will do anything other than blame the malice of the bridge's opponents for its failure. It will be interesting to watch the accusations and counter-accusations over the next few weeks, but I'll be surprised if anything more comes of it than that.

One folly may be at an end, but the folly that led to it will continue to resurface on projects of this ilk, those that are only kept afloat by delusions of grandeur and by their ability to skirt proper scrutiny.

*(for non-UK readers, see here, and I'm only joking).

23 April 2017

Has the irresistible force finally met the immovable object?

As the Garden Bridge saga appears to be drawing to an ignominious conclusion, it's a good time to ask how much this sorry tale owes to simple incompetence and how much to a more flagrant disregard of consequence.

It's a good time because Margaret Hodge’s recent report into the project lays bare many of its failings.

Hodge's report is incisive and damning. The Garden Bridge Trust's response to it is feeble-minded and exemplifies the wilful deafness to criticism which has marched the entire project into a mire of failure.

Hodge has, probably sensibly, avoided any consideration of whether the world's most expensive flowerpots would be a "good thing", although there is much to criticise here.

In principle, the idea of a garden above the Thames has some merit, but it must be offset against its adverse impacts. Published views of the bridge usually adopt a pigeon's perspective, disguising the extent to which this massive structure would blot out views across and along the river. I also think that we should all have had enough of privatised public spaces subsidised with public money, and like other heavily-surveilled areas of "public" realm, it is difficult to see the case for taxpayers funding a new garden so hemmed about with constraints on use as this one is.

If it doesn't properly consider value, the Hodge report does at least consider value for money. When the project's designers were appointed in mid-2013, the bridge was estimated to cost £60m, more than double the cost of any previous or projected footbridge elsewhere on the Thames in London. At this stage, the fee for the lead designers was anticipate to be £4m (roughly 7% of capital cost, already a very high figure for a team who would not actually deliver the detailed design).

Just one year later in June 2014, the total cost had mushroomed to some £159m. By July 2015, the sum had hit £175m, then £185m in August 2016. The Garden Bridge Trust has more recently confirmed the likely final figure to "substantially exceed" that figure, with a sum "north of £200m" reported to Margaret Hodge during the preparation of her report. And yet, the project has rolled steadily onwards, with some £46m now spent or committed without a spade so much as hovering over the ground (indeed, the detailed design of the bridge is not yet complete). This is a steam-roller set in motion but seemingly without anyone sitting in the driving seat.

Cost escalation can arise for many reasons, but chief amongst them on projects of this sort is simply that initial estimates were wrong. Scope and risks are not understood properly at an early stage, project promoters are biased towards optimism, and we are all reliant on a QS industry which isn't fit-for-purpose. There are few meaningful benchmarks for iconic projects so it's not a disgrace that the initial estimate was wrong. It is, however, a disgrace that the project was not stopped when its true costs began to emerge, and it remains a disgrace that nobody involved has the balls to stop it now as costs continue to rise.

At the same time as costs have risen, funding available has actually decreased. Although the government funding bodies have meekly handed over yet more cash every time their funding ceiling has been breached, the private funders on whom the project ultimately relies have been backing off. In spring 2015, donors had pledged £85m towards the scheme; by August 2016, the total pledge had dropped to £69m and has not increased since.

We are witnessing the collision of an irresistible force with an immovable object. The force originates in the vanity and ego of the project's promoters, principally the much-lampooned Boris Johnson. This was facilitated by a cultural failing, an uncritical adulation of celebrities (in this case, Joanna Lumley and Thomas Heatherwick) which diminishes what few critical faculties our public bodies can bring to bear at the best of times. Once the beast has been set in motion, it is simply "face" that continues to propel it forwards, the false hope that eventual project success will vindicate the troubled journey. We've also seen, writ horribly large, the sunk cost fallacy, with several of the project's fans noting that so much money has been spent, it would simply be wasted if the project were now to cease.

It seems overwhelmingly likely that it will now be wasted: £46m of public money pissed into the Thames without any of those responsible having to suffer the just consequences of their monumental failure.

The seemingly irresistible force is hitting its immovable object: the money simply isn't there. The government and current mayor have hedged their bets even as the costs continue to mount, readying their excuses for abandoning this sinking ship.

Sometimes when costs escalate, they can be tolerated on the grounds of the project's final value, an economist's totting up of the public benefit. That has been attempted here, with a business case thrown together in May 2014 after the project was already well underway, with design team appointed, costs rising, and up to £60m of public funding already announced. Hodge rubbishes the business case, which had already been found to be questionable and weak by central government.

One of the most damning aspects of Hodge's report is her criticism of the appointment of the project design team. I think this is symptomatic of a much wider failure of accountability and effective project control, exemplified by the lack of a properly motivated driver at the controls of the steam-roller, anyone who would feel it in their own pocket when things went wrong.

Hodge records that in March 2013 Heatherwick Studio was appointed to design the bridge, having won a quickly concocted procurement exercise against Marks Barfield and Wilkinson Eyre. This particular farrago has been dissected elsewhere, so I'll just summarise the key points. The three competitors were invited to bid for a "feasibility study", despite the fact that Heatherwick had been discussing the project with the London Mayor since July 2012, and seems to have already had a giant flower-point design stuffed down a back-pocket.

Hodge's report documents in detail what a farce this procurement exercise was, with several iterations of a briefing document showing how Heatherwick's key role was openly acknowledged then gradually cut out to ensure that a "neutral" procurement document could be presented to others.

I'll take the position that the evaluation of the tenders was utterly incompetent, but frankly it stinks of worse, and clients are normally careful to avoid such an impression. Heatherwick Studio scored above the other contenders both on "relevant design experience" and "understanding of the brief". On the first point it seems inarguable that Heatherwick actually demonstrated the weakest relevant experience to conducting a footbridge feasibility study. The commercial evaluation was even more of a joke, with Heatherwick's proposed fee of £173,000 dwarfing the other two proposals (£49,939 and £15,125). The client team sought clarification from Heatherwick, who then significantly reduced their fee, allowing them to win the work.

Heatherwick have been paid over £2.6m for their work on the project, which may sound like a lot of money, but will sound like a lot more if it turns out to be for something that is never built.

The appointment of the project's engineer and project manager seems to have been little better. Thirteen consultancies bid for this role, with Arup winning in July 2013. Arup had already been working with Heatherwick Studio, but they were placed only 7th in the initial tender evaluation due to the level of their fee. Despite this, they were included among 5 bidders shortlisted for further consideration. Of those, Arup were the only bidder contacted specifically and asked to revise their charges, which they did before then being appointed.

Elsewhere in Hodge's report, she notes that the key official most most directly responsible for both procurement decisions had come from Arup to Transport for London, and subsequently returned to Arup in 2016.

As of April 2015, Arup had been paid £8.4m for their work, and I would not be surprised if the total has now reached eight figures. There must have been some interesting discussions about "change control" given that the original funding authorised to commence design (for both architect and engineer combined) was only £4m. The £8.4m fee is only about 4% of the latest forecast capital cost, which might seem reasonable given that the detailed design is being done by others (as part of the design-and-build contract), but it's still a struggle to imagine quite what all that money was spent on.

There is much more of interest in Margaret Hodge’s report, and I recommend it to anyone interested in how grand and foolish projects of this type are procured. It should certainly be required reading for anyone with direct responsibility for procurement or project management of schemes which are iconic, vanity-driven or otherwise dubious in real merit.

If the current Mayor of London decides to proceed further with the Garden Bridge, then he is clearly a fool, and he will join the long list of those associated with the scheme who will have stood watch while costs continue to escalate. If as, seems more likely, he decides it is time to throw in the towel and cease providing financial support, an almighty mess can be expected to ensue.

Without financial support from Transport for London, the Garden Bridge Trust, which is already barely a going concern, cannot continue. TfL and the Department for Transport have already under-written the Trust’s cancellation liabilities, but these are capped and I suspect will not be resolved cleanly. There has been a contractor appointed since March 2016 (Bouygues), who in turn have a designer and who are presumably not carrying any of the risk of project cancellation. They will wish to be paid in full for all their costs incurred.

Much of TfL's funding for the project is in the form of a loan to the Garden Bridge Trust, which would be written off. All this would form part of the estimated £46m of taxpayers' funding which will never be recovered.

The blame game that will commence will then form the real interest. Teflon-shouldered Boris, and the ever-defensive coterie of Garden Bridge zealots, will blame the project's failure on the naysayers and the (sadly accurate) prophets of doom, and will never accept or acknowledge their own role in this all-too-avoidable fiasco. The many individuals whose incompetence and cowardice enabled it all to happen are likely to get off scot-free.

If history can tell us anything, it is that flagrant malfeasance shall have no consequences, and that lessons will be stated clearly but not learned. I'm reminded, inevitably, of Sunderland’s River Wear Crossing fiasco, with its overly-ambitious iconic design, the deafness of all involved to external criticism, and the millions of pounds pointlessly wasted. Those responsible in that case also suffered no consequence.

Readers may also fondly recall Glasgow's Broomielaw to Tradeston footbridge, where the promoter again ploughed on despite expert criticism, before eventually being forced to abandon increasingly expensive plans. I discussed the invulnerability of the Garden Bridge's ambitious yet deluded proponents to reasonable criticism in a previous post.

The culture of impunity enjoyed by the celebrity-addled nincompoops who are appointed to, supposedly, spend our money wisely, seems unlikely to change any time soon. They will not even feel the shame that they so clearly ought to, the loss of face is too much to contemplate.

I would hope, however, that the various professions and professionals involved in this and other similarly sorry stories might pause to consider the ethics of our own positions.

Can we simply say that it is the fault of the farmer for providing us with an over-sized trough from which to guzzle? Are we right to say that decisions on what to spend and how to spend it are for the promoters and politicians, and we will simply close our eyes and hold our noses and follow their bidding? Are we also too eager to be blinded by glamour and the excitement of association?

More positively, what are we doing to assist our clients and the wider public to understand our project risks, to understand the primacy of project value, and to help them with better evidence so that they can make better decisions, ideally before the steam-roller is ever put into gear?

Previous posts
Garden Bridge proposed in London
£4m to design white elephant
Heatherwick's Garden Bridge gains planning consent from Lambeth Council
London's Garden Bridge: grumbling rumbles on, but here's a wrinkle
London's Garden Bridge: to build, or not to build?

31 March 2017

The Great White Hoop: Five years of the Margaret Hunt Hill Bridge

Here's an interesting article on a Calatrava bridge in Dallas, Texas. I don't like the bridge, but the piece offers an interesting perspective on the limitations of building such a monumental structure without any real regard to its context. I'm mainly sharing the link, however, because there are some excellent photos at the end of the article.


19 March 2017

"The Ha'penny Bridge, Dublin" by Michael English

In a recent post, I reviewed Annette Black and Michael Barry's "Bridges of Dublin", a survey of the many bridges spanning the River Liffey in Ireland's capital city. This time, I've been reading a rather more singular volume.

"The Ha'penny Bridge, Dublin" (Dublin City Council / Four Courts Press, 272pp, 2016) [amazon.co.uk] documents only one of Dublin's bridges, although certainly the best known.

Built in 1816, the Ha'penny Bridge (named for its toll) was the first iron bridge in Ireland. It was designed and fabricated by the Coalbrookdale foundry in Shropshire, the same as had built the pioneering Iron Bridge in 1779. The new crossing replaced an existing ferry, and was promoted by the ferry proprietors William Walsh and John Claudius Beresford as a private initiative.

The bridge has survived two centuries of often eventful Irish history, and this book wisely takes a very open-ended approach to documenting its subject.

The author, Michael English, is a graphic designer and photographer, and the book is beautifully presented and laid out throughout. It is filled with depictions of the bridge in art and photography, both historical and contemporary, and many of the excellent photographs are the author's. There are pictures of souvenirs, bridge poems, anecdotes, a plethora of directly and indirectly relevant material. In this respect it is a truly exemplary publication: any bridge would be proud to be recorded in this manner.

Different authors contribute different chapters to the book. The text drives onto, across, beneath and away from the bridge; treating it as a vantage point to explore the bridge, its surroundings, and its context from many angles.

David de Haan offers a history of Coalbrookdale, source of Englands' best known iron bridge, and of the cast iron shipped to Dublin. This explains everything from the iron smelting process to the broader industrial transformation which allowed iron to challenge stone for economy. Gerard Smyth recounts the main points of the bridge's history, while Logan Sisley describes the the fortunately ill-fated 1913 plan to replace the bridge with the Hugh Lane Gallery.

Michael English recounts the history of some of the people who passed beneath the bridge most often: the Guinness company, whose barges transported Guinness stout below the bridge for many years. Annette Black offers a more cultural history of the bridge, probably my favourite chapter. It's a history of the bridge, but also a history of Dublin with the bridge as merely a convenient nexus. For me, this gets under the skin both of the bridge and the city: the bridge is not a monument, or an icon, but a site which features in people's everyday lives, a home to the homeless as much as a crossing for others.

I was a little disappointed in Michael Barry's chapter describing the bridge's 1998-2001 refurbishment and restoration. There are a few extracts from drawings and one engineering diagram, but I felt there was just too little detail on what appears to have been a very sensitive and carefully-considered project.

The penultimate chapter, by architect Seán Harrington, describes his design of Dublin's Millennium Bridge, now one of the main places from which to view the Ha'penny Bridge, and a structure where the various differences and similarities are constructive. The final chapter consists of Michael English's photographs of the bridge taken at different times of day and different periods in the year. These are excellent, well portraying way in which such a simple structure can appear so very different as hours and seasons pass.

Although the book is extensive in its coverage, one area where it is lacking is in any discussion of the Ha'penny Bridge's siblings. The distinctive form of its cast iron ribs, with two layers of quadrilateral braced ribs (like the more modern Vierendeel girder), was not new in 1816, indeed the appearance of the bridge was essentially a copy of Thomas Telford and Thomas Stanton's Meole Brace bridge, completed in Shropshire in 1811 and supplied by William Hazledine. The same or very similar design was used again in 1813 for the Cantlop Bridge, and then repeated after completion of the Ha'penny Bridge, in 1818 for the Cound Bridge (now reconstructed in Telford) and in 1823 at Stokesay. If you look at close-up images of Cantlop Bridge, the relationship is very clear.

Overall, however, this is an excellent book, highly relevant to anyone with an interest in Dublin or in bridges, particularly the role that they play in urban history. As already noted, it's a very attractive book, exceptionally well-illustrated, and a great example of what can be produced by people who allow their passion for a subject to drive what they do.

14 March 2017

Winner announced in Upper Orwell Crossings competition

The winner of Suffolk County Council's competition to choose an architect for two new bridges across the Upper Orwell has been announced as Foster and Partners.

I discussed this RIBA-organised contest at length last August, and again in September. You may recall that this is not a conventional bridge design competition: it's quite possible that the winner's designs will never get built. It was a contest to select an architect to partner the project's engineering consultant, WSP | Parsons Brinckerhoff, who had already been selected.

There was much to criticise in how the contest was initially set up: its limitation to large firms (overturned after protests), the desire for an arranged marriage rather than allowing natural design partnerships to form, and the intention for architects to demonstrate their worth in isolation i.e. without actually working with the project's engineer. Of the various shortlisted firms, several either had internal engineering expertise anyway or brought along their own choice of partner.

As originally promoted, entrants had to submit two entries for both bridges required, and would be evaluated 40% on price. I wonder whether these criteria survived, as only one design has been released from the winner, and they do not have the reputation of charging at the bottom of the scale. Alternatively, maybe they were the cheapest, and the design presented was only second best. I think we may never know.

It's difficult to comment in detail on what can be seen of the winning design. Without drawings or context, they say little. However, a few things are clear.

The competition jury appears to have treated this like a conventional contest: they praise the "economical elegance" of the designs, and comment specifically on how pedestrian routes have been integrated with the highway bridges. On both bridges, the walkway / cycleway is a separate structure tacked onto the main bridge, although not gratuitously, instead allowing the designer to consider what is best for different flow preferences.

The high-level bridge is the more exotic of the two, reminding me of a treetop walkway, with the non-motorised path nestled at the top of giant steel tree-trunks and below the fumes of the highway canopy. It has an expensive rather than structurally rational appearance, and in this regard it's interesting to read what local MP Ben Gummer has to say:
"The fact that we will have what will be a globally recognised bridge of beauty will say something powerful about our town's ambition and our place not just in our county, or our region, or our country, but in the world."
At the risk of offending locals, this is Ipswich, not Paris or Geneva. It's hard not to wonder how well a forced marriage between the incumbent consultant and a big-name architect will work. Ambition should not be scoffed at, but I do wonder whether Ipswich really needs something world-class, or whether they would have been better to set their sights a little lower.

The RIBA Competitions office has a track record of limited success (6 out 8 competition-winning bridges were never built), so it will also be interesting to see whether the Upper Orwell Crossings project bucks that particular trend.

17 February 2017

"Bridges of Dublin" by Annette Black & Michael B Barry

Dublin City Council seem to have done a good job recognising the importance to the City (and tourists) of the city's River Liffey, and not only the river but the many bridges which cross it. They maintain an excellent website devoted to these structures, which includes not just informative material, but plenty of bridge-related stories and a substantial insight into bridge history and engineering generally.

The City Council has also published a series of books on the city's engineering history (in cooperation with Four Courts Press). "Bridges of Dublin: the remarkable story of Dublin's Liffey Bridges" (Dublin City Council / Four Courts Press, 256pp, 2015) [amazon.co.uk] is to some extent the in-print companion to the Bridges of Dublin website, and also owes a debt to Michael Phillips and Albert Hamilton's paper Project history of Dublin's River Liffey Bridges, published in the ICE's Bridge Engineering journal.

The book covers 24 structures in detail, every span across the Liffey from Lucan Bridge to the sea.

Each bridge is documented with a large 2-page photo (generally of excellent quality), often an aerial image, a location map, and a range of other images including drawings, historical paintings and etchings, and old photographs. More recent structures are often accompanied by photographs taken during construction.

The associated text provides not just a history of each bridge, or the stories associated with it, but something of a history of Dublin and wider Ireland. Most of Dublin's bridges were built in the 18th and 19th centuries, the period starting with the Acts of Union of 1801, and including the Irish War of Independence and Civil War of the 1920s.

Emblematic of the role of the various bridges as political symbols, many of the spans have been renamed at key points in history. An example is the Rory O'More Bridge, renamed in 1939 after a 17th century Irish rebel leader. The bridge had previously been renamed the Emancipation Bridge in 1929 (the centenary of Catholic Emancipation), having originally been named the Victoria and Albert Bridge when first opened in 1861. This repeated renaming recurs throughout the book, and makes an interesting contrasts to other cities, such as London, where the need to mark major political change has been absent.

The bridges also encapsulate a history of engineering, as in many major and historic cities. The oldest surviving bridge is Mellows Bridge, a three-span masonry arch structure completed in 1768 to a design by military surveyor Charles Vallancey. However, older bridges crossed the Liffey in both timber and stone, and more recent structures include spans in cast iron, wrought iron, early steel, reinforced concrete, prestressed concrete, and modern steel. The most recent spans include highly contemporary structures such as the James Joyce Bridge, Samuel Beckett Bridge, and Seán O'Casey Bridge.

Much of the interest in Bridges of Dublin is in the ability to see so clearly the many historical, technical and architectural differences between the many structures, as well as their close similarities and relationships.

The text is generally good at providing some structural engineering detail for those with a more technological interest, and at crediting designers and builders. The text is not critical in nature, but is highly informative.

In addition to the sections on each bridge, there is an introduction by City Engineer Michael Phillips, which primarily relates the history of bridge engineering, and a useful chapter which sites the history of the bridges more clearly in context with the history of the city and its river (again accompanied by some very well reproduced historical images). Guides are given to two possible walking tours for the main city bridges, and a series of technical drawings are included covering key bridges, although these are reproduced too small to be of much value.

Overall, this is a very impressive book, not only for students of Dublin's architectural and engineering history, but for anyone with an interest in bridges. There are few books which bring so much well-researched information together with such an excellent range of imagery, and I can definitely recommend it to interested pontists.

06 February 2017

Calatrava in Greenwich

Plans have been announced for Santiago Calatrava's second bridge in the UK (the first being 1995's Trinity Footbridge). Yes, there's a whole load of other stuff as well, some yuppie flats and a super-sized greenhouse, but that's not what you read the Happy Pontist for, is it?

Ok, a little context. Calatrava's "Peninsula Place" is just part of a huge £8.4bn redevelopment of London's Greenwich Peninsula, albeit a key part as it includes the gateway underground station. The development is somewhat controversial, largely because of the very small proportion of "affordable" housing which is to be included, following pressure from the developers.

Calatrava's scheme is as grandiose as you would expect. The bridge is intended to link his part of the site, with station and apartment blocks, to the riverside.

It's a cable-stayed structure, so tall that they couldn't even fit all of it into one of the publicity images. In much of Calatrava's recent career the designer seems to have been largely rehashing all his older ideas, while making his designs steadily bigger and steadily more illogical. In line with this principal, he has chosen to stitch together two previous designs to make this new one: Calgary's Peace Bridge, and Valencia's Serreria Bridge.

Frankenstein would have been proud.

The bridge somewhat resembles a giant white snake shedding its skin, rearing up like some kind of super-sized horror-film monstrosity. It's far from clear what it actually spans (only a cycleway is shown in the visualisations), but it seems unlikely that it needs to be this big for functional reasons: like many of Calatrava's recent bridges, its giganticism seems purely symbolic.

The mast is restrained by a single vertical cable, necessitating enormous foundations to counter-balance the main span. (Perhaps it's also symbolic: look, the success of this enterprise is hanging by a thread.)

The curvature of the mast is to some extent structurally rational, as it reduced bending moments and hence should in theory slightly reduce the amount of steelwork required.

The main span is a tubular truss, with metalwork arranged in an intersecting helix, which evokes a futuristic sensibility without actually being structurally sensible in any way: there's a Jane Austen joke in there somewhere, I'm sure.

From the images, it seems as if the mast is on the riverside, which feels the wrong way round to me: the more visually and physically massive part of the bridge should be anchored further inland, I think.

Assuming this entire project doesn't go belly-up following an Brexit or Trump-related economic meltdown, I'm confident this will be a very interesting scheme to watch over the next few years.

04 February 2017

Deux livres sur les passerelles à Paris

I'll conclude my series of posts on the bridges of Paris with mentions for a couple more relevant books.

"Passerelle Simone-de-Beauvour, Paris" (Archives d'Achitecture Moderne, 128pp, 2006) is written by Armelle Lavalou, Francoise Lamarre and Jean-Paul Robert, and credited to the bridge's architect, Feichtinger Architectes.

It's a well-illustrated volume with text in both English and French throughout. It's filled with images of the completed bridge as well as its construction, but sadly the book is not large, measuring only 24cm by 16cm, which leaves some of the imagery and diagrams a little small.

The bridge is explained both in terms of its architecture and its engineering, although the explanation of the engineering is aimed squarely at non-technical readers: I was left with plenty of questions. A number of somewhat diagrammatic drawings are included, which are very interesting but without dimensions and again missing some of the details that would better explain how the bridge works.

There are some lovely pictures of competition-stage physical models and design-stage wind-tunnel test, which I'd like to have seen reproduced at much larger size. For me, the best section covers the construction of the bridge, including its static and dynamic load testing.

The book acknowledges the participation of RFR, the structural engineers, without giving them detailed credit, very much giving the impression that they were the subsidiary partner. I don't know whether this is a fair reflection or not.

Overall, it's an essential book for anyone wanting to learn more about this spectacular bridge, but it could have been much better.

"Passerelle Solferino Paris / Solferino Bridge Paris" (Birkhauser, 128pp, 2001) by Francoise Fromonot has the same page count but a larger format (30cm by 23cm). It is also well-illustrated, with shared French and English text. I didn't visit this bridge during my recent trip to Paris, but I thought it was worth featuring the book here anyway.

The core of the book has less text, giving more space to images of the design competition, the bridge under construction, and the completed span. The larger format works well for these.

The key attraction, for me at least, is the inclusion of a lengthy section covering the engineering design and construction issues, which gives extensive and numerical detail on key points such as foundation loads, vibration modes, steel grades etc. While I'm sure this is of limited interest to some readers, it opens up the opportunity for specialists to much better understand the merits of the design.

The book also features a number of detailed design drawings, which are fascinating because of the bridge's extensive geometric complexity. Indeed, perhaps the only thing missing here is a more critical voice, as this is a bridge which was criticised from several quarters, both for the complexity of its fabrication as well as its dynamic behaviour and initial lack of slip resistance.

Nonetheless, it's a thorough and well-presented book, and I can recommend it to anyone interested in this bridge.

29 January 2017

"Bridges of Paris" by Michael Saint James

This book offers a big contrast to The Glow of Paris, reviewed in my last post, even though ostensibly its subject is the same.

Both books are hefty coffee table photographic surveys of the river bridges of central Paris. Glow squeezes 35 bridges into 208 pages, while Michael Saint James's Bridges of Paris fits 37 bridges into 280 pages (Citron Bay Press, 280pp, 2015).

The photographs in Glow are all taken at night, in black-and-white, and in a fine tradition of photography which takes as its subject landscape, architecture, and light. The Bridges of Paris is more varied in approach and style.

Most photos are taken in daytime, some on short exposure, and others on long exposure, traffic and pedestrians becoming only a blurred presence. Most photos are reproduced in full-page size, but there are also plenty of smaller photos, taking in not just overviews of the bridges but also details such as sculpture or love-locks.

Each bridge is accompanied by an explanatory text giving key facts (dates and dimensions) as well as something of each structure's history. There are satellite maps to locate the bridges, and a very nice introduction with several reproductions of historical paintings of key bridges.

However, the main attraction to this book is its focus on the bridges not only as beautiful architecture, but as lived spaces. Most of the photographs include people using the bridges, people looking at the bridges, people looking out from the bridges. In several photographs you'd hardly know there was a bridge there at all: they focus on how they provide public spaces, occupied by artists, street traders and performers.

The quality of the photography is probably more uneven than in Glow, but there are some stunning photographs in Bridges of Paris, and the sheer variety shows how each bridge's character changes with season, time of day and weather.

There is more information on the book at its dedicated website. US readers can pick the book up fairly easily from amazon.com (currently at a significantly discounted price). Readers elsewhere may find it more difficult to get hold of, but for any admirer of Paris and its bridges, I think it's certainly worth the effort - it's an excellent book.

26 January 2017

"The Glow of Paris - The Bridges of Paris at Night" by Gary Zuercher

Having spent the last few posts on a whistlestop tour of some of the bridges of Paris, I'm going to round things off by featuring a few particularly relevant books which I consulted.

Gary Zuercher's The Glow of Paris - The Bridges of Paris at Night (Marcorp Editions, 208pp, 2015) [amazon.co.uk] is a photographic survey of the 35 bridges which span the Seine between the points where it is crossed by the Boulevard Périphérique.

It's a serious coffee-table tome, 30cm square, with all the photographs reproduced at least full page size. They are all in black-and-white and all photographed at night.

The photos have generally been shot on a long exposure, which gives a landscape quality to the bridges, softening the sky and river and eliminating fast traffic and pedestrians. Indeed, the images are posed to remove signs of life as far as possible, to focus on the structures and their context. This is clearly a conscious choice, and while it ensures bridges are depicted clearly and beautifully, it does divorce them from the cityscape as a lived space rather than merely a collection of stone and steel.

There is a good mixture of scales, from wide open shots depicting bridges in their setting, through to close-ups of architectural details. Throughout, the emphasis is on the interaction of form and light.

The book includes maps to help the reader understand where each bridge is, and each bridge is accompanied by typically a couple of pages text, describing the bridge's history and any interesting stories about it. These are aimed at the general reader, but are informative enough for all but the most serious bridge enthusiast. I referred to them quite a bit while preparing my Paris blog posts, although I did have to look elsewhere for more detail. The text isn't referenced, but it's simply not that kind of book!

I very much enjoyed the book and am really glad to have it on my shelves now. Taken together, the bridges cover a long and varied period of history, with numerous different materials, technologies and architectural styles. The photographs are excellent, and the book is recommended for admirers of photography, Paris, bridges, or all three.

There's an interview with Gary Zuercher about the book online, and you can find out more about it at his website, including many more sample images than I've had space for here.

24 January 2017

French Bridges: 19. Passerelle Simone-de-Beauvoir, Paris

This is the last in my current series of Parisian bridges. I started with the oldest bridge over the Seine in central Paris, the Pont Neuf, and I'll finish with the newest, the Passerelle Simone-de-Beauvoir.

A design competition was organised in 1998 for a new crossing of the Seine, halfway between the existing Pont de Bercy and Pont de Tolbiac. The new bridge would link the Parc de Bercy with the National Library of France, as well as the riverbanks, which are here somewhat isolated from the rest of the cityscape by busy highways. Both park and library are like large plateaus situated well above river bank level.

Five teams were invited to submit designs: Tadao Ando / Setec TPI; SEEE / Patrick Berger; Marc Mimram; Arup / RFR / Chris Wilkinson; and Deitmar Feichtinger / RFR. In March 1999, the partnership of Feichtinger and RFR were declared the winner.

The winning proposal connects the riverbanks at lower and upper levels and avoids any supports in the river. The structure is therefore not also the latest bridge across the Seine, but also easily the longest span, with a 194m span between piers, and a total length of 304m. The deck is a generous 12m wide in total, although over most of its length this is split at different levels, so for practical purposes it's only 6m wide. The bridge was completed in 2006 at a total cost of 21 million euros.

By any standard, the bridge is enormous. I think it's particularly instructive to compare it to Patrick Berger's proposal, which was for a variant on a conventional suspension / stress ribbon bridge. This would have required substantially less material over the river, giving a lighter and less redundant appearance, but would have needed enormous anchorage structures well beyond the ends of the bridge itself.

Feichtinger's design (I'm going to call it his for the sake of shorthand, although clearly it was the result of a team effort) can be conceptualised structurally in several different ways. Think of a lenticular truss (like the Royal Albert Bridge, or the Maryhill House Footbridge). This can be thought of as a truss, with upper and lower chords carrying compression and tension, as well as shear forces by virtue of their inclination. It can also, however, be seen as an underspanned self-anchored suspension bridge, where a suspension cable below-deck is anchored not into the ground, but against the deck, which provides a balancing thrust.

The Passerelle Simone-de-Beauvoir is essentially the same type of bridge, except that the ends of the main span members, instead of meeting at a point where the forces balance, have been displaced vertically. The result of this is that although the horizontal forces from the suspension element and the compression arch element are broadly in balance, they are applied eccentrically, creating large overturning moments at both riverbank supports.

The overturning is restrained by a coupled foundation: the tension member passes vertically over a saddle, and into a deep anchor foundation. The saddle is balanced by an inclined leg, which connects directly to the ends of the main arch element. At this point, in a perfect world the horizontal forces would balance precisely. However, the suspension cable is significantly longer than the arch, and the forces do not balance, so there is a further inclined leg below the arch to carry the vertical loads from the bridge into the ground, via a massive deep caisson foundation. Taken together, the upper and lower inclined legs can be nicknamed the "boomerang".

For a pure lenticular truss of the same span, the foundation loads are vastly smaller, as the vertical load on the two foundations is equal to a half-share of the vertical weight of the bridge and whatever it carries. For the Passerelle Simone-de-Beauvoir, the main foundations must support the same vertical load, but must also react against the anchorage force, so the foundations are much more heavily loaded. However, the benefit is obvious: a much shallower structural form and one which better ties together the various ground levels. A lenticular truss of 194m span would sit ridiculously high in the air and look completely inappropriate.

The observant reader will, of course, have noted that the central part of the bridge is indeed a conventional lenticular truss, with upper and lower balancing elements coming together at a point. Indeed, this part of the bridge was fabricated precisely in this way: as an independent structure, fabricated elsewhere, assembled into its whole, and shipped up river ready for erection. In this respect, the structure can be seen as different structural form: the Gerber beam.

This concept was named after Gottfried Heinrich Gerber, whose idea was to take a continuous beam and insert hinges at the points of inflection in the diagram of bending moments (the points of theoretically zero moment). This transforms a structure which is complex to analyse into one which is simple to analyse, as well as eliminating troublesome side-effects of bending continuity such as vulnerability to foundation settlements. However, it retains the main advantage of continuity, which is reduced bending moments relative to simply-supported bridges. The exact position of the hinges is to some extent arbitrary, as the position of the theoretical points of inflection depends on the nature and position of loads applied to the span.

The central lenticular truss of the Passerelle is 106m long, and is structurally highly-efficient, just like the drop-in span of a Gerber beam. Here, the drop-in section is held aloft by cantilever structures either side, so another way to conceptualise this bridge structure is as an unbalanced cantilever bridge, like taking a single span of the Forth Railway Bridge and splitting it off from the rest by taking a giant machete down the centreline of the two towers. It's easy to image how much work would be required to haul back the severed towers and stop them from from simply toppling into the Forth Estuary, and that gives a good idea for how hard the Passerelle Simone-de-Beauvoir is working towards the same end.

One issue for the designers will have been how to combine the catenary and arch elements in a structurally and visually sensible manner. Catenary and suspension bridges typically employ circular cables as their main tension elements, but the Passerelle instead uses grade 355 steel plate as the tension elements, which although structurally inefficient makes visual sense.

These plates are 100mm thick at midspan, and 150mm over the anchor saddles, where they split into three bands before being anchored into the foundations. The plates are 1m wide, so each one can carry up to about 5000 tonnes without breaking. Each catenary can therefore carry the weight of roughly 15 fully-laden jumbo jets, which gives some idea quite how hard the bridge and its foundations are working. For comparison, this is a total tension load of roughly five times the total cable forces on London's Millennium Bridge, which is both shorter and narrower and lacks the arch element.

The tension plates are separated from the arches by bundles of four steel rods, which the architect nicknamed "obelisks". Compare the much smaller Maryhill House Footbridge, which has triangular struts in a similar arrangement, with the "pointy" end of the strut on the tension member and the thick end on the compression member. This creates a semi-Vierendeel arrangement, using the bending stiffness of the connection to the thicker compression element to prevent longitudinal movement and hence ensure the lenticular truss behaves as a fully integrated deep beam.

The bridge has two end spans across the adjacent highways which are more straightforward fishbelly trusses. These sit on the abutments at one end, and at the other are connected onto the main bridge saddle zones. If you compare the various photos, you'll see that the detailing of these areas is quite tricky, and the designers have generally done a very good job in keeping everything as simple as they can.

As with other long-span footbridges, the Passerelle Simone-de-Beauvoir could have been vulnerable to vibration. I didn't spot them on my visit, but there are tuned mass dampers below the decks to address flexural and torsional movements, and viscous dampers at the ends of the bridge to reduce longitudinal movement. Extensive crowd testing was undertaken to ensure these would perform correctly, and the bridge was also tested under static loads by filling 550 water tanks laid out along the length of the deck.

The layout of the bridge is not entirely as rational as it first appears. Although the upper deck surface follows precisely the contours of the structural form, the lower deck does not. At its ends, it sits at a higher level than the arch elements, a departure from the competition-winning scheme. Presumably, it just didn't prove possible to get the structural requirements properly matched against the topography of the site.

The bridge reminds me of the great wooden rollercoasters of the USA. As you walk onto the upper deck from the end, you at first see a wide expanse of timber and can't at first see the rest of the bridge. As you go further, great sweeping waves of bridge gradually rise into view. The change in perception of the structure is charming, and more so once you discover the ramps which lead both downwards and off the bridge and also down below the central crown.

Here, you find a sheltered and very different space, somewhere you can pause, rest, meet people, or contemplate the view. It's a shame that there's no seating at either level, as this is a bridge which is clearly as much about the creation of generous public space as it is about getting from A to B. It's a space which invites alternative uses, and has been used on several occasions for art events.

For me, the most interesting thing about the Passerelle Simone-de-Beauvoir is the relationship between its lightness and its massiveness. It's a structural design intended to maximise efficiency over a long span - the words "slender", "lightness" and "ribbon-like" are used in the architect's book describing the structure. I certainly admire the bridge's generosity of space, but it's this which for me also makes the bridge appear massive and heavy, something that I think is simply unavoidable for such a wide structure. However efficient the design, there's an accumulation of surface and metalwork which creates an enormous, unavoidably massive presence within the river surroundings.

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