Bridge criticism 8: The good, the bad, and the ugly

The previous post in this thread discussed the modernist article of faith that informs most engineering criticism: that bridges should be economic, efficient, and elegant. Extravagance, frivolity, and massiveness are not qualities that most engineers look for or admire. Lyne Rail Bridge (over the M25 near London, pictured right) was at one time voted by civil engineers as the ugliest bridge in Britain: it may or may not be economic, but it's certainly not elegant, and its squat, brutal presence offends most engineers.

There have been a number of attempts over the years to set out criteria against which the success or failure of a bridge design can be judged (beyond the mere ability to stand up or to not wobble alarmingly).

As previously discussed, Alan Holgate and Bill Addis both suggested several criteria, while concluding that there can be no single, simple prescription.

For the students at Bath, their analysis of each bridge involves the production of outline calculations. This both demonstrates an understanding of the structural behaviour, and allows comment on a bridge's structural efficiency. This is an excellent discipline for students, as it teaches them to consider the structure holistically, an antidote to the very close focus on individual structural elements that is common to much undergraduate teaching. It also emphasises the way in which great engineers often deal with the core of a problem by very much simplified calculations, and how these can be used to prove a structure’s feasibility without going into detail.

Clearly however, it's unreasonable to expect parallel calculations to form part of anything other than the most detailed reviews of a modern bridge (examples which do go that far include Spiro Pollalis's What is a bridge?, which analyses Santiago Calatrava's Alamillo Bridge [example bending moment diagram pictured left], and Françoise Fromonot's Passerelle Solferino Paris).

In the modern design environment, it seems unlikely a critic can offer more accurate calculations than a design's originator, especially without access to comprehensive detailed drawings. There will be cases where it's appropriate to use simple calculations to estimate the key forces on a structure, and to consider whether an alternative geometry would lead to a better distribution of forces. It's clearly also appropriate to carry out an analysis of a structure that predates modern techniques, to discover how efficient a design may be in the light of current knowledge (an example being Woodruff and Billington’s analysis of Maillart's Töss Bridge in a paper previously discussed).

Any wider consideration of a bridge’s technical or aesthetic success will be based on a set of a priori assumptions, or a design philosophy. This should be stated openly, as the modernist dogma common to many structural engineers (particularly bridge engineers, who have less experience of compromise with architectural demands) should not go unchallenged.

In the rest of is post, and the ones that follow, I'm going to cover the philosophies put forward by some of the greatest bridge designers of the last century: Santiago Calatrava, Fritz Leonhardt, Christian Menn, and Michel Virlogeux.

At the 1992 Royal Fine Art Commission seminar on bridge design (long out of print, but pictured right), Santiago Calatrava considered the keys to good design proposed by Marcus Vitruvius to remain relevant today:

"There are three concepts, three keys to be found in the books. One concept is utilitas, which means utility, the second is firmitas, which means stability, and the third is venustas, which means beauty. These are the three key aspects with which any work built by man can be analysed."

Calatrava notes that the Renaissance bishop Daniel Barbaro, who translated Vitruvius, suggested three further considerations, namely fortitude (strength), bonitas (goodness) and intellectus (intelligence). According to Calatrava:

"This is very interesting, because when we discuss the aesthetics of something that primarily has to be stable, we can only link beauty and stability with intelligence."

While these offer timeless principles that underlie good design, they would seem to be so subjective as to offer little assistance to the critical reviewer.

Taking Calatrava's own bridges as examples, is the Puente de la Mujer in Buenos Aires useful? Stable? Beautiful? Strong? Good? Or intelligent?

This is an asymmetrical cable-stayed swing bridge (pictured, left, image courtesy of FJTU on flickr), where the pylon inclines towards the deck. By implication there is considerable deception going on, as an enormous counterweight must be hidden at the base of the pylon, but is hardly expressed visually. To me, it looks barely stable and while I wouldn't deny its beauty, I would find the terms good and intelligent hard to apply to it in any way.

It's a case where the balance between sculptural expression and structural common-sense has tipped so far, it's fallen completely off the scale.

It's also a case where the designer's actions speak louder than his words.

Next up: Fritz Leonhardt

Bridges news roundup

Lots of big posts in preparation, so just time for a short interlude with some recent (and some slightly stale) bridge news:

Auditor eyes 'iconic' bridge
Calgary footbridge procurement to be scrutinised

Business bosses still back bridge
Iconic River Wear crossing retains support

Unusual bridges and bridge-building games
Blogger spots bridges - runs risk of becoming bridge nerd

Worlds most dangerous bridges
Serviceability limit state applied differently around the world

Wind tunnel foot bridge

Michael Jantzen is an architectural artist who seems to specialise in unbuilt (and often unbuildable) follies. This one is a footbridge in the form of a walkthrough wind turbine, pictured below. An earlier proposal is even less likely to ever be built ...

Bridge criticism 7: Moralists on the march

In the previous posting in this thread, I discussed the public criticism (and it's lack of assistance to the unfortunate client) surrounding the Glasgowbridge competition. For this post, I'm going to cover an instance of criticism from a technical paper, very different in tone, of no assistance to the designer or client, but possibly of wider interest to the design community.

The Sundial Bridge is a cable-stayed footbridge designed by Santiago Calatrava and opened in 2004 in the Turtle Bay Exploration Park near Redding in California (shown right; all images of the bridge are courtesy of informedmindstravel on flickr). The bridge’s 66m pylon is inclined away from the deck, which it supports without the use of back-stays. It has some similarities to Calatrava's Alamillo Bridge, although at Turtle Bay the pylon is offset to one side of the deck rather than aligned with the centreline.

Sundial Bridge cost $23 million to build, mostly funded by a private foundation. According to Turtle Bay, “in addition to being a functional work of art, the bridge is a technical marvel as well”.

Much of the public commentary on the bridge has been very positive. To take just one example:

"It’s a wonderfully calibrated delight, an artistic feat of engineering that resembles nothing around it except perhaps the angled neck of an egret rising from the riverbank towards the sky." (San Francisco Chronicle)

There has been some public criticism of the bridge’s cost, which increased considerably from the earliest estimates. The cost is substantially in excess of that for many other comparable architect-led footbridges. However, the bridge is more unusual in that it has been the subject of a detailed published critique by fellow professional engineers.

In a paper titled "Aesthetics and Ethics in Pedestrian Bridge Design" (Footbridge 2005 conference, sadly not available online), David Billington and Shawn Woodruff argue that "the drive for landmark bridges has led some engineers to disregard the engineering ethic of economy with some recent footbridges". In their extensive paper, they note that its cost per square metre is more than double that of the Solferino Bridge (while still less than half that of the London Millennium Bridge). Their table of costs (in US$) is shown below:

In criticising the bridge, they make very clear their assumptions about the philosophy of structural engineering:

"A couple of engineers have made the assumption that due to their small size and form, pedestrian bridges are not necessarily constrained by economics. This is simply incorrect. It is the engineer’s ethic to design with economy in mind, whether one is designing for a public entity or for a massive private corporation … the most successful footbridges are those that satisfy the ideals of structural art. Structural art is a disciplined art form independent to architecture. It has three dimensions: scientific, social, and symbolic, with each having a specific measure: scientific = efficiency, social = economy, symbolic = elegance. To be a work of structural art, a structure must satisfy each of these three ideals."

I'm not entirely sure from which holy scripture comes the dictate that economy is ethical, nor that the best bridges are those which match Billington's prescriptions for "structural art". These considerations deny the simple fact that in ordinary life value is not merely monetary, or that the quality of a bridge should be judged by the experience of its users rather than the interests of its designers.

To explain the structure’s high cost, Billington and Woodruff note several issues with its engineering design:

"Enormous bending moments are created in the deck near the tower and also in the tower due to the lack of back stays for both pylons. The omission of these stays creates a need for large pylons with much material to take the large bending moments. Ironically the structure which appears light when viewed from afar is actually much heavier than it could be with the inclusion of just a single backstay."

Their criticism of the structural behaviour is left implicit; it's the lack of efficiency and hence high cost to which Billington and Woodruff clearly object.

Their paper is unusual in that it is a formal critique on engineering grounds, but it focuses mainly on cost and is not thorough in its criticism. The authors imply they have carried out a finite element analysis but offer no details. They mention the "irrationality of the entire form", and on the subject of construction they say:

"The understanding and visualization of the tower was aided through actual physical models, but the intense three dimensional geometry and the multiple planes of plates, stiffeners, and cables still made the process unnecessarily difficult."

That "unnecessarily" is odd: if the geometry is unusual, then clearly fabrication will be less straightforward. But where does the necessity come from? To a structural engineer, the offset pylon is "unnecessary", because a central pylon would have reduced torsion and simplified design detailing (considerably). But is the pedestrian experience on such a bridge better? (For more on the difficulties of construction, including more extracts from the design drawings like the one shown left, see Scott Melnick's Sun Sculpture [PDF]).

In many ways, the criticisms read like the complaint of the stolid engineer whose inherent conservatism has been offended. They take as read the assumption that it would be better to simplify the geometry than to invest additional money to achieve it, however this assumes the bridge’s function to be entirely that of carrying people across an obstacle.

Billington and Woodruff don't really offer any way to evaluate the bridge's aesthetic success, and the economics are taken solely as the cost of construction, with no attempt to quantify the benefits to the local economy in terms of tourism or other revenue.

The possibility that a piece of sculpture could hold intrinsic value separate from its role in the economy or position in the art market is not entertained – for the bridge engineer, it seems everything must come down to the relationship between cost and functionality.

Billington & Woodruff offer a direct contrast to the Sundial Bridge in Robert Maillart’s reinforced concrete arch Töss footbridge (shown right), which they rightly describe as elegant, efficient, and economical. In this, they rely to a great extent on their own structural analysis to demonstrate its material efficiency. However, no attempt is made to ask whether a bridge of this style would have provided the same value to Turtle Bay as did Calatrava.

It may seem that the criticism of the Sundial Bridge shows engineers still to occupy the modernist paradigm of the mid-twentieth century, while the broader culture has moved on and accepted that form and function have a more complex relationship. As suggested by the title of their paper, Billington & Woodruff are moral puritans who regard "correct" structural engineering as a matter of basic ethics.

Should structural engineering criticism limit itself to technical matters or can it attempt to address wider concerns? Even Billington & Woodruff draw aesthetics into their set of base criteria by citing elegance as a mark of good engineering, while their concept of economy can readily be expanded to address matters beyond cost and functionality, particularly if recast as value rather than cost.

I have considerable sympathy for the criticisms of this bridge: from the structural point of view, it's a monumental folly, with the 14m deep foundations alone grossly out of scale to the needs of a simple river crossing. There's little doubt that an attractive, striking bridge could have been built for a fifth of the cost.

But I don't think that extravagance is inherently unethical - nor, no doubt, does anyone admiring the pyramids, Mount Rushmore, the Roden crater, or any of thousands of other artistic interventions in the landscape. If engineering criticism is to take its place alongside architectural debate, more than just the standard modernist dogma will be needed.

Bridge criticism 6: Too little, too late

In a series of recent posts, I've wondered why there's so little public criticism of poor bridge design. Perhaps engineers feel restrained by institutional ethics, perhaps there are too few models for engineering criticism, perhaps it's a matter of education.

But although there's very little public criticism, there is some. In this and the next post, I'll discuss two examples of the various critiques that do take place, one on the theme of When Bridge Design Competitions Go Bad, and the other taken from the more rarefied realms of a technical paper. Both suggest that while criticism is alive, it isn't necessary very well.

In 2003, a competition was held to design a new footbridge across the River Clyde in Glasgow. Ive previously posted in more detail about the competition and the various designs entered.

The winning design, by Atkins and Richard Rogers, featured a deck elliptically curved in plan, supported from a steel arch inclined above and towards the deck (see image). In turn, the arch is supported by tie-back cables. It was, by any standard, a very unusual structural form, probably unique.


The arch sloped at an angle of 26° (it had been 22° in the competition submission, but was increased during detailed design to try and get it to work), far shallower than most inclined arch bridges, which in any event generally have the arch sloping away from the deck to counterbalance its weight, and so that both elements stiffen each other.

The finished design also introduced props to the arch (shown right), again suggesting that the basic concept was flawed.

There's an excellent published account of the design process ("The Evolution of the Structure for Glasgowbridge”, Footbridge 2005 conference, December 2005), unfortunately not available online, which makes it clear that several decisions on the structural form were driven by the architects, and that the competition period allowed insufficient time for the analyses the engineer would like to have carried out. This is nothing unusual for design competitions, indeed, it's the norm!

For example, the paper says:

"The architects began looking at other masted structures"

"on further consideration, the architects felt that the angular form of the twin masts did not sit comfortably with the curvature of the deck"

"If we had had more time in the closing days of the competition we would have liked to have carried out some analyses on the arch angle, however there was no time to change the model or the architectural drawings so the angle remained at 22 degrees"

The image on the right shows one of the many variants the design went through as it was developed.

Published criticism of the design when the winner was first announced was very limited and largely limited to architectural critics and losing competitors. In the former camp, Penny Lewis of Prospect magazine said in the Scotsman (21 November 2003):

"I thought it was the scheme that had the highest number of clichés."

Representing the losers, architect Alan Dunlop was quoted in the same newspaper:

"It was most disappointing of all to have lost to that bridge. I wish the city well and I hope it comes off, but we went through every possible permutation about who was going to win this competition and we never even considered Neptune’s Way. That’s how flabbergasted we are by this."

The public were even less impressed, at least judging from the letters pages of Glasgow's papers:

"WHAT a ridiculous bridge! It has been described as a "long way for a short cut". Imagine trying to cross it in our horizontal Scottish rain. This is not London. Being in such an exposed location it should have been enclosed." (Niall Barker, Glasgow Herald, 24/11/03)

"Whatever the architectural merits (and I personally think the elliptical design is impractical and frankly stupid), this bridge will be completely useless as an economic stimulus to the city, and will turn out to be a massive £40m white elephant." (Iain Mann, Glasgow Herald, 1/12/03)

"True to form, Foster [sic] can't just span a river – he has to take a long sweeping way round. For what reason? Not function; seemingly he thinks it will look good. Well, it won't. All it will look like is an architect who doesn't understand engineering trying a poor imitation of Calatrava." (John McNeil, Glasgow Herald, 3/12/03)

The design was put out to tender, but the only two tenders received were both in excess of budget, and the design was quickly dropped by the client, Glasgow City Council.

At this stage, the design’s engineering principles received greater public criticism, although still relatively limited in extent.

Writing in a letter to New Civil Engineer (30 March 2006), Cezary Bednarski was “astonished by the winning design as it was clearly unworkable and hugely expensive”, while in the same issue of NCE David Collings suggested “that the Glasgow footbridge is over budget is not surprising – structurally it is an appalling design”. Neither criticism offered more detail.

So was this another case of sour grapes (like Alan Dunlop, Bednarski was one of the unsuccessful competitors), or even just the benefit of hindsight? I think neither - they are fair viewpoints, just far too late to be of any help to anybody.

Generating innovative concepts without the time to properly test their feasibility is always a risky business, and developing the Glasgowbridge concept was clearly always going to be difficult. I reckon that was apparent to most bridge engineering specialists throughout.

Clearly, in this case, the project outcome might be traced back to the robustness of the competition jury’s decision-making process. However, I wonder whether the promoter might have been greatly assisted, if anyone had stuck their head above the parapet at a much earlier stage. This could have been facilitated in several ways: the client could have sought a peer review of the unusual design from another firm; they could even have sought comments on each design from the other competitors.

But ultimately, what is needed is a bridge engineering community where people have the courage to speak their mind publicly. This will always be difficult where commercial interests encourage silence, but the institutions could assist by revising their ethical instructions, which don't help. Academics, slightly less restrained by commercial issues, should also seek a louder voice on design issues (as is the case elsewhere in the world).

Having said all that, in the case of Glasgowbridge, I suspect that whatever criticism was voiced, the client would not have listened, as they seemed fixated on their Gateshead-rivalling dream, and defensive about its merits.

Bridge competition debris part 9: Peabody Trust Habitable Bridge

Updated 8/Feb/09: New Edward Cullinan images added (all copyright Edward Cullinan Architects)

The Peabody Trust is a London-based social housing charity, founded in the 19th century by philanthropist George Peabody. As part of their efforts to provide affordable housing in the city, they've been involved in at least two bridge design proposals over the years.

They promoted a design by Cartwright Pickard for a landmark inhabited bridge at Leamouth in east London (pictured left, this is one of many bridge schemes at Leamouth to fall by the wayside over the years, in this case being dropped in 2002).

They also ran a competition for an inhabited bridge across the Thames between St Pauls Cathedral and Bankside in 1995 (later to become the site of the infamous Millennium Bridge), and that's the subject of this post.

The Peabody Trust sought to promote "the bridge as urban hamlet", asking the competitors for "a subtle interweaving of concepts relating to structure, urban design, relationships between cost and value, and the quality of life that should be possible in the heart of London".

It's hard to tell how serious anyone really was about the scheme, although inhabited bridges were certainly in the air at the time, with a separate competition elsewhere on the Thames organised by the Royal Academy the following year, and exhibitions at both the Royal Academy and the Centre Pompidou.

Six firms were invited to submit entries, and so far as I can tell, no winner was declared. All the entries are documented in the Living Bridges book, published by the Royal Academy on the occasion of their own competition and accompanying exhibition. Where I haven't been able to find images of the bridges elsewhere, I've taken them from the book (with the Peabody Trust's permission, for the images they hold copyright on).

I've credited the firms mentioned in Living Bridges, although I imagine others were involved, especially on the engineering side. However, unlike many more recent bridge design competitions, the architects involved for the Peabody contest were generally notable more for their building work than for their bridges.

To a great extent, it looks like some entrants saw the bridge was seen as incidental, as a necessary evil in creating a site for waterside (or over-water) housing.

Comparisons with the great inhabited bridges (Old London Bridge, pictured, and Ponte Vecchio) may be instructive, particularly for the entries here which shirked the challenge of actually siting the housing on the bridge itself. While that's sensible from a practical viewpoint (e.g. provision of sewerage and access for emergency services) it falls short of the romantic idea of a habitable bridge.

Levitt Bernstein, Hunt Thompson, Allies and Morrison and Edward Cullinan all offered elegant modern bridges, but merely as an afterthought to riverside or river pier apartment blocks. This is the docklands model - urbane, genteel, but hard to get very excited about. There's hardly any shortage of riverside apartments in London, after all, and these designs omit the key element which made London Bridge and the Ponte Vecchio unique communities - the focus on a street.

John Outram bucked the trend with an admirably idiosyncratic anti-modernist whimsy which did at least echo the classical living bridge ideal, but which could never have been built in 90s London, however much the neo-classicists fought against the prevailing mood.

Richard Horden's design also succeeded in keeping the housing on the bridge, albeit in an elongated greenhouse fitted out with renewable energy systems. This was probably my favourite - it has less visual impact than Outram's proposal, but I think more openness to the elements would be essential in a prominent location like this.

The entries
Levitt Bernstein Associates


Edward Cullinan and Associates


Hunt Thompson Associates


John Outram Associates / Whitby Bird


Allies and Morrison


Richard Horden Associates / Mott MacDonald / ETH Zurich

Bridge competition debris part 8: Rijnhavenbrug

In December last year, a winner was announced in a competition to design a new moveable footbridge in Rotterdam. My Dutch is non-existent so in what follows below I apologise for any omissions or errors that may have been introduced courtesy of Google Translate.

In late 2007, the search began for a suitable design for a proposed bridge connecting the area of Katendrecht to Wilhemina Pier. Although it was to be primarily a footbridge, it also has to provide access to emergency vehicles.

In February 2008, five design firms were invited to provide preliminary ideas: Bolles & Wilson, DISSING+WEITLING, Quist Wintermans, Bureau SLA / DHV / Delcan, and ZUS. By October, the list had narrowed to three, and those three designs were made available for public consultation.

SLA appeared particularly aggrieved at being dropped from the final three, issuing an angry press release [PDF] which has been extensively picked up elsewhere on the web:

"Rotterdam thinks the bureau SLA design is very innovative, but also - very difficult. Bureau SLA, with their engineering consultants DHV and Delcan, are asked for extended calculations. The city can hardly believe it: this bridge will not collapse? More calculations and details are asked for. The city’s engineers still cannot believe it. This is too difficult, surely this is madness! The best thing to do and be done with the whole conundrum is to disqualify the entry. And so it happened. The jury, consisting of Holland’s finest designers, are told not to look upon the scary bridge any further and Bureau SLA are expelled from participation in the competition."

It's far from clear which judging criterion SLA actually contravened (if any). Nonetheless, SLA's bridge has an uncommonly ambitious opening mechanism - hydraulic arms are required to pull in the two main bridge spans from a flat position, gradually raising them up into the air like a pair of scissors. The hydraulics not only have to operate from an extremely shallow angle, vastly multiplying the forces involved, but also lift the entire bridge weight without the benefit of any counterweight.

Moveable bridges almost always involve a counterweight so as to reduce loads on the opening mechanism and hence both construction and operational costs. So while the SLA design concept may well be feasible, it's certainly more risky and likely to be far more expensive than the proposals that did get shortlisted. While the design is certainly spectacular, it's worth noting that the competition criteria specifically requested a bridge which was not iconic.

SLA doth protest too much, methinks.

Following selection of Quist Wintermans as the winner, it's expected that construction will commence in late 2009, with the bridge opened in 2011. Their design is a conventional hydraulically operated counterweighted bascule bridge, with the main point of interest being the way the span is offset from the pivot point in a trowel-handle manner. It's a nice design, modest and appealing in its simplicity.

The competition website is http://www.rijnhavenbrug.nl/, which has extensive details of the three shortlisted designs. Below, I've included images of all the entries I can find, i.e. all except for Bolles & Wilson.

Of the two losing designs, DISSING+WEITLING's is even more modest than the winner, with the orange stripe seemingly an effort to offset this. The ZUS design incorporates habitable towers, which contravenes the competition's requirement for a flat, unimposing structure. I find the very traditional overhead-leaf bascule design somewhat unconvincing: there are lots of bridges of that type in Europe and it gives the impression that more thought was given to the buildings than the bridge span itself.

Winner

Quist Wintermans

Shortlisted

DISSING+WEITLING

ZUS

Other entries

Bureau SLA

Bridge criticism 5: Criticism as a learning tool

In a recent post, I noted that structural engineering degree courses make little or no attempt to help students develop a critical attitude to design quality. They're given little if any tuition on aesthetic issues, and it's doubtful how much they really learn from design projects.

Design projects are usually artificially simplified to match them to the abilities of the students. I know from experience that these projects are difficult for academics to mark, as designs that would never see the light of day in real life may still need to be marked well if students at least show they understand key issues such as buildability. The end result is that while students often enjoy their design projects, I doubt that they actually learn much of long-term value about the design process, whether that's the interpersonal dynamics of design teams, or techniques for jump-starting creative thought.

While few in the field would see this as an opportunity to introduce a confrontational "crit" such as architects undergo, it could be an opportunity for student peers to challenge each other’s work. This would encourage them to analyse the merits of their own designs more thoroughly, and also open them to alternative ideas and options that they may not have considered. Such a process clearly needs to be facilitated in such a manner that criticism is constructive.

One question is whether they could learn more about design without actually having to do it. In professional life, there's little doubt that we learn as much from considering other people's designs as from the process of developing our own.

This approach is being included as part of a bridge engineering course at the University of Bath directed by Professor Tim Ibell. In this course students are asked to collect data on an existing bridge, critically analyse its aesthetics, carry out a simple structural assessment, and comment on how it was built and whether better alternatives were available. The aesthetic analysis is based on a set of formal considerations set out by Fritz Leonhardt in his book Brücken. The resulting papers offer a comprehensive critical review of each structure, combining both objective and quantifiable issues with matters which can only be treated subjectively.

I personally believe the focus on existing structures may give students a greater understanding of the challenges of bridge design than does the conventional student design exercise. They have to consider how design choices have been made, without being asked to make choices for which they lack sufficient knowledge and experience.

As well as improving their understanding of bridge engineering and of the design process, the course must encourage them to be more confident in forming and expressing opinions on structural engineering.

The student papers from 2007 and 2008 are available online, and cover bridges as wide-ranging as Brooklyn Bridge, the Millau Viaduct, Sunniberg Bridge, the Clyde Arc and the Menai Suspension Bridge. They generally make interesting reading - you get a real sense of the students beginning to understand structural engineering beyond the confines of the calculator, although inevitably many of the judgements presented are either mistaken or in some cases plain daft.

The value of the "case study" approach is its realism - it forces students to confront real problems of buildability, aesthetics of real structures, in a way that never works as well with the creations of their own imagination. I think it would be great if more universities would take up this idea!