Bridge criticism 11: The French Connection

The last three posts in this series have covered the views on "good bridge design" of Santiago Calatrava, Fritz Leonhardt, and Christian Menn, all of them amongst the great bridge designers of the last century.

Unusually forthright views were presented by French engineer Michel Virlogeux in a 1996 paper, "Bridges and the structural art" (available online). Virlogeux worked on the Pont de Normandie (pictured right, image courtesy of Francoise Roche on flickr), and is probably best known for designing the Millau Viaduct.

I've previously discussed David Billington's ideas on bridge design, which suggest that for a bridge to be "good", it must be elegant, efficient and economic. Like Leonhardt and Menn, Billington is opposed to extravagance, and to bridges which pay little heed to a structural optimum.

Virlogeux does not agree:

"Of course, David Billington is strongly influenced by the American philosophy of life, based on the individuals and on economy ... Economy has been too much the unique goal of narrow-minded engineers, resulting in some poor, ugly and repetitive structures which discredited the profession ... Engineers used to live in their narrow professional world, sure of a legitimacy based on rationality and competence. They have not been able to feel the evolution of our Society and the growing power of politicians and media, and of the lobbies which are able to influence them."

While advocating that engineers adopt a wider view, this is not to detract from "good" structural engineering, but to ensure that structural engineers have a greater voice in design:

"Structural engineers failed in having access to those who take the decisions, and it is not surprising that the result is often poor as regards structural projects in the recent years. The most striking is that design competitions have been organized for some bridge projects - when bridges are the essence of engineering art - which were only open to architects or in which engineers had only a limited role and no responsibility. Resulting in some clear disasters."

In essence, Virlogeux still adheres to the engineering party line, that structures should be efficient and never dishonest. Writing about Marc Mimram's Solférino Footbridge (pictured right, image courtesy of Etienne Cazin on flickr), he comments that:

"fantasy governed the detailed design, a fantasy which had not been tempered by the rationality of a serious engineer; the arches, for an example, are made of inclined I-shaped beams with totally irrational details. There is no web - for transparency - just a series of diaphragms, and the members are transversely curved, [which] obliged these beams [to be] made from cast steel elements ... back to the 19th Century and to enormous costs."

Virlogeux's prescriptions for a successful bridge design are that it be:

• structurally efficient, and sometimes innovative
• expressive of the state-of-the art in construction methods
• built with perfection and elegance as a goal
• built by the most eminent builders
• in agreement with its surroundings

As may be obvious, Virlogeux is refreshing in his willingness to criticise his fellow engineers. From the same paper, there comes this example:

"We take an example from the World Exhibition in Sevilla to evidence such a difference, with the two major bridges built on this occasion: the Alamillo Bridge, which can be considered an attractive sculpture, but which is a total nonsense structurally, and the Barqueta Bridge [image courtesy of Guillermo Vale on flickr] designed by Juan Jose Arenas, a real structure which shows the natural flow of forces, and which is elegant and efficient in the same time."

So, it turns out, that while Virlogeux does not think engineers should be slaves to economy, there is nonetheless a moral imperative to avoid structural inefficiency:

"These monstrous errors must be systematically denounced to avoid their repetition, and to convince that excellence in bridge design can only come from a rational structural organization. Unfortunately, even some good architects who used to work efficiently with engineers are going in the wrong direction when they are given the responsibility of design. What is wrong? - too much searching for originality, aiming at producing a surprise more than trying to develop a pure structural design which is not, by essence, in their real competence.

"Modesty must be considered again a quality!"

This sense of anger seems to drive many bridge engineers commenting on bridge aesthetics in the last couple of decades. It is not entirely directed at the increasingly key role of architects in landmark bridge design, but also at clients and the wider society for promoting that focus. Hardly anyone wins a bridge design competition with a simple, efficient bridge of a form that has been used many times before. The anger is also provoked by a sense of loss, as bridge engineers are simply not used to having their controlling role in design usurped by others.

Ultimately, however, these debates are not about the interests of architects or engineers, but about whether bridge design serves the wider public well. The public do not care if a bridge design is structurally inefficient - but they do care if it is ugly, or if it requires far more of their money than an alternative. Virlogeux's focus on the principles of good structural design is only helpful where it serves these demands.

So, from all of this, is there any useful guidance as to how we can evaluate good bridge design, how we can criticise poor design? The expressed philosophies of the four designers I've highlighted are all subtly different, but all fundamentally derived from modernism and a belief that efficiency or economy is a moral rather than a purely commercial requirement. Personally, I think there should be room for idiosyncrasy, eccentricity, bravado, and even humour from time time - so long as there is accountability, and people understand both what they are paying for, and what the alternatives really are. This isn't the case as often as it should be.

Calatrava seems to have paid little heed to the Vitruvian ideals that he espoused twenty-five years ago, and his willingness to ignore prevailing wisdom remains admirable however ridiculous some of the resulting structures have been. There's room in this world both for Calatrava's flamboyant structure-as-sculpture, and for the elegant exploitation of structural behaviour that characterises many other bridge designers. I think the challenge is to make the public, and the clients who spend their money, really understand the choices that are available, and the real consequences of those choices in cost and risk. That will require better procurement processes, more visible structural engineers, and undoubtedly more public criticism of bridge design, both good and bad.

Bridge criticism 10: Of Mice and Menn

In recent posts, I've discussed the views of Santiago Calatrava and Fritz Leonhardt on what makes a good bridge design. This time, it's the turn of the great Swiss designer Christian Menn, who was responsible for the excellent Sunniberg Bridge, amongst others.

Some engineers are highly prescriptive in their views on bridge aesthetics, and Menn is undoubtedly one. In his paper "Functional Shaping of Piers and Pylons" (in Structural Engineering International, 1998), Menn wrote:

"A truly well designed bridge balances economy and aesthetics while responding to the functional requirements and technical and environmental boundary conditions."

Menn considers the "functional requirements" to comprise the traffic, alignment and state-of-the art construction technologies. The "technical and environmental boundary conditions" include topography, geology, clearances, available programme, emission limits, impacts on adjacent buildings etc.

Menn continues:

"On the basis of the above considerations, the real art of bridge design is to elaborate a suitable technically appropriate structural system that aims at achieving an optimal balance of economy and appearance …This pragmatic, simple and purely functional approach not only leads to technically proper structures but also to aesthetically convincing ones."

According to Menn, any significant increase in cost above the "least expensive functional solution" (a 5% premium for larger bridges, or 20% for medium bridges) is unacceptable and "should be abandoned". (Image, right, of Menn's Boston bridge courtest of Ken Douglas at flickr, showing non-functional pylon caps).

Menn’s opinion is common amongst bridge engineers, with one typical example being the Billington & Woodruff paper discussed in a previous post. This moralistic position is also shared by Leonhardt.

Menn’s is the language of moral puritanism – bridges must be "proper"; ornamentation is improper; cost must be minimised; the most appropriate structural system will inevitably produce the best bridge. This back-to-basics approach continues to offer much of value in an age where architect-led bridge design has produced schemes which are unaffordable or unmaintainable, but it should not be the only game in town.

It's doubtful that in the modern era the assumption that a "simple and purely functional approach" automatically leads to "aesthetically convincing" structures. Writers such as Billington offer the greatest praise for the structures of designers such as Maillart, Candela, Nervi or Isler, but the conditions of production for such structures have changed irrevocably. These structures, for which the identification of an optimal form allowed forces and materials to be minimised, come from an age where least cost arose from least materials, and hence a technically efficient design would often coincide with one which is slender and elegant. Even in this pre-modern period, however, there were structures which are highly inefficient structurally yet which have become much loved icons, such as the Forth Railway Bridge (pictured above right, courtesy of Simon Bradshaw at flickr).

Modern technology has changed the conditions for least cost. In particular, mass-production, pre-fabrication, and automation mean that in most cases the least-cost solution is one that minimises site labour and maximises the use of off-site fabrication and assembly. In this situation, a parallel-flanged beam may cost less than a beam shaped to fit its bending moments, even though more material is used. Many structures which were efficient to construct have also been found to be expensive to maintain, and a structure with a lower whole life cost may well have higher initial cost e.g. the use of concrete and hence heavier foundations to avoid the cost of repainting structural steelwork.

The further difficulty with Menn’s prescription is the issue of public opinion. While there may be some common ground amongst structural engineers as to what constitutes a good design, it is far from clear whether our idea of good design is shared by the public who benefit from a bridge and who fund its construction. For example, the public may be thought to delight in Calatrava’s white skeletal frameworks, even though the costs of fabricating these complex geometries must frequently result in a project that greatly exceeds Menn’s "least expensive functional solution".

Ironically, of course, Calatrava was Menn's student, and Menn was rich in praise for him initially.

Who are engineers to judge the success of such a bridge if their opinion departs from the end-user? While clearly there are areas where engineers have expertise the public do not (on both capital cost and particularly on the likely maintenance liabilities), we should not deceive ourselves into thinking that a concentration on functionality automatically produces the "best" bridge.

Next: Michel Virlogeux

Bridge criticism 9: Bridge aesthetics by numbers

In the previous post, I took a look at Santiago Calatrava's prescriptions for how the quality of bridge design can be judged. Often seen as the flamboyant flamenco dancer of the bridge design community, Calatrava contrasts greatly with Fritz Leonhardt, the subject of this post, and someone perhaps seen as the personification of a far more sober, Germanic tendency.

Leonhardt's monumental book "Brücken", first published in 1982, offered a ten-point framework for the consideration of bridge aesthetics. This was a subject of lifelong interest to the great German engineer (pictured above left), who wrote about it several times and participated in an attempt by IABSE to publish a manual on the subject.

Leonhardt proposed the following concepts as matters to be considered in bridge aesthetics:

1. Fulfilment of purpose/function
2. Proportion
3. Order
4. Refinement of form
5. Integration into the environment
6. Surface texture
7. Colour
8. Character
9. Complexity
10. Incorporating nature

Leonhardt’s framework remains useful today (and is used as the basis of the Bath University work discussed previously), and allows for a considerable degree of subjectivity. However, it falls prey to the usual engineer's fallacy that everything, including aesthetics, can be reduced to a set of neat rules. Leonhardt's view on this drew squarely on tradition (you can find it excerpted from "Brücken" online in his contribution to "Bridge Aesthetics Around the World"):

"The [recognized masterpieces of architecture] reveal certain characteristics, such as proportion, symmetry, rhythm, repetition, contrast, and similar factors. The master schools of old, such as those of Vitruvius and Palladio, had rules or guidelines for these characteristics. Surely these guidelines are still valid today ..."

In the same text, Leonhardt summarised his ten rules, and explicitly linked them to an ethical mandate:

"Aesthetics and ethics are in a sense related ... Ethics also implies humility and modesty, virtues that we find lacking in many designers of the last few decades; they have been replaced by a tendency toward the spectacular, the sensational and the gigantic. Because of exaggerated ambition and vanity, and spurred by the desire to impress, these designers created unnecessary fashions, lacking true qualities of beauty".

Leonhardt was undoubtedly the arch-puritan when it came to bridge design.

Most of "Brücken" expands in great detail on the application of his framework to all types of bridges and their component parts. Even today it remains a very useful reference, although it's a shame that it's both out-of-print and generally expensive secondhand.

It's clear that many of Leonhardt’s conclusions reflect only his own opinion, even if that opinion often coincides with the common view amongst engineers. Writing about Robert Maillart's three-pinned arch structures such as Salginatobel bridge, he claimed that "these Maillart-type arch bridges only look good in special situations as here over a gorge and against a mountainous background." Having seen at least one, Rossgraben Bridge (pictured left), in a different setting, I'd find it hard to agree with that.

Discussing Matti Ollila's Myllysilta bridge, a very slender arch/beam bridge in Turku, Finland (pictured right), Leonhardt commands: "Do not try to imitate it; to do so one has to be a master, fully aware of all possible influences like creep of concrete etc". Okay, that's those of us in the lower ranks told, then.

None of this should be taken to indicate that Leonhardt was nothing but an old fuddy-duddy, with little to offer on how bridges can be evaluated today. On the contrary, he was undoubtedly one of the greatest bridge engineers of all time, and he was a great explainer of how small changes to bridge design could improve appearance considerably. His orthodox but highly detailed understanding of bridge aesthetics has much to offer as a way of evaluating any bridge today - if there's anything to be wary of, it's simply his linking of aesthetics to ethics, the idea that following a particular set of rules was a moral imperative.

Next: Christian Menn.

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

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 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!

Bridge criticism 4: Teaching engineers to criticise

In the last post on this topic, I covered Alan Holgate's ideas for a practice of structural engineering criticism. Holgate's book The Art in Structural Design was aimed largely at engineering students, to give them a better idea of the "softer" aspects of engineering which are often largely absent from an undergraduate education.

Architecture students are often given a very harsh introduction to the idea that their designs are subject to criticism, with the institution of the architectural "crit" whereby their designs are reviewed by their tutors in front of the class. In theory, this is to provide constructive criticism of flaws in design, and to prepare them for the real world where clients will often have very strong views on the merits of designs they are paying for. In practice, it's seen by many students as nothing but an ordeal, a trial by fire (see cartoon).

Engineering students generally experience nothing of this sort. In a future post, I intend to discuss an excellent example where structural engineering students are being explicitly introduced to the value of criticism. For now, however, I'd like to cover some proposals that Bill Addis made back in 1996.

In his paper "Structural criticism and the aesthetics of structures" (IABSE 15th Congress, available online), Addis (pictured, right) noted the absence of critical evaluation of design from undergraduate education:

"In the light of ... the recent fashion for clients to appoint architects to lead bridge design teams, it is perhap time to consider what engineers might do to establish their territory more firmly".

Addis notes that students of the humanities are immersed in criticism of the works that they study, and that this helps them develop:

• a critical vocabulary


• the ability to discriminate aesthetically


• willingness to express their self

Addis's view of how limited most structural engineering students are with these facilities is as true now as it was in 1996:

"The engineer's weakness in these areas should scarcely be surprising, given the content of most engineering courses, the typical educational background of many engineering students, their poor ability to communicate effectively and with confidence, and the very few opportunities they are given to develop such skills by talking eloquently about structures and design. The activity of structural criticism can provide such opportunities."

Addis doesn't suggest that student engineers should be subjected to anything like the crit. Instead, he suggests they could be asked to take two existing structures, describing them visually, structurally, environmentally; discuss their feelings about the structures; and write a comparative evaluation.

He offers several criteria students can use to carry out their evaluation. Examples include:

• skill and clarity with which structural actions are expressed


• elegance or simplicity


• expression of solidity or delicacy


• expression in geometry of the imposed loads and internal forces


• interaction between load-bearing and non-load-bearing aspects

My own experience in working with universities is that few have taken these ideas on board. There is so much technology and analysis in the curriculum that there is little time to cover the philosophy of design other than to hope that it somehow emerges magically from design exercises. Again in my experience, it doesn't - students are so preoccupied with the details of their projects that they have little opportunity to sit back and reflect on the wider lessons from the design process.

It's also clearly the case that few academics teaching structural engineering have substantial experience in a design office any more. Their backgrounds predispose them to teaching topics that can be simply measured and evaluated, mathematical topics, and to shy away from having to judge subjective views on aesthetics or design quality.

New graduates continue to arrive in the workplace with little or no knowledge of engineering history, of the great designers, of how to design (rather than analyse), and of how they might take responsibility for engineering in any way other than as a responsive technician (usually the architect's servant).

Addis concludes:

"to be a good structural engineer it is essential to be able to discriminate between good and bad examples of structural engineering. In the context of structural engineering, any concern with aesthetics should be addressing the question as to what constitutes good and bad design and what it is to be a good structural engineer."

Fortunately, the outlook isn't entirely bleak. In a later post, I'll cover examples of how structural engineering criticism is now being cultivated at university, something that many others would benefit from taking on board. And how does all this relate to bridges? Well, I'll get back to that too, although perhaps not immediately!

Bridge criticism 3: What would structural engineering criticism look like?

In recent posts I've wondered why poor bridge designs receive so little public criticism.

If you go back into the times of the Stephensons, Telfords and Brunels it seems engineers were considerably more willing to critique each other's ideas openly*. Perhaps the ethical constraints were less formal then, but I'd guess one main change is readier recourse to the libel law in modern times.

However, I wonder not only why there is so little public criticism, but what would it actually be like if there were more? Architectural criticism is a well-trodden field, but engineering criticism is a barely-explored jungle.

One of the few writers to have explored the possibilities for a practice of structural engineering criticism is Alan Holgate. Another is Bill Addis, and I may well return to him in a later post.

In his 1992 book The Aesthetics of Built Form, Holgate quotes Le Corbusier's somewhat ridiculous view on engineers:

"Shall we see engineers trying to turn themselves into men of aesthetic sensibility? That would be a real danger ... An engineer should stay fixed, and remain a calculator, for his particular justification is to remain within the confines of pure reason."

Many engineers even today would like to ignore aesthetics, unless it can be codified into series of rules and principles. But engineers should really be best placed to judge the merits of bridge designs, and that should include efficiency, economy and also aesthetic value.

In his earlier 1986 book, The Art in Structural Design, Holgate had considered how to develop and promote engineering criticism that could be distinct from architectural criticism. The entire book is available online, and it's well worth a read. He suggested three typical objections to the whole idea of criticism in the structural engineering field (most quotes below are from the same chapter - just follow that link):

• Criticism is necessarily destructive


• Critics are not as competent as the practitioner


• Any unique design is too complex for anyone other than those directly involved to properly appraise

Each of these points can however be addressed: engineers are usually keen to learn from their own and others’ experience, for example, and often someone remote from the details of design can provide a view untarnished by tunnel vision.

Holgate proposed three means by which the quality of structural criticism could be maximised.

• The critic should be educated to a reasonable degree in the relevant areas


• They should have an educated audience


• They should have as much information as possible about the design problem and solution

Frequently, the third of these is the hardest to achieve, as full details of only a few designs are published. Even where a design is documented in a technical paper, it rarely discusses the choices made in the design process in great depth.

There are examples of published engineering criticism (e.g. David Billington & Shawn Woodruff's review of Calatrava's Sundial Bridge) which try to deal with this by carrying out their own analysis of selected structures. I'll cover some of these in a later post. However, it's hard to see how their judgement of the balance between aesthetic integrity and cost is intrinsically superior to the designer’s judgements on the same matters.

Holgate suggested that better-informed criticism would be possible if designers could be encouraged to be more open about the process by which they identify a solution. However, this could be hindered by embarrassment, commercial sensitivity, and fear of litigation. He concluded:

“Hence a considerable amount of courage may be required on the part of the designers in providing the critic with the information necessary to make a fair appraisal of their skill in solving the structural problem. On the other hand designers can hardly blame the critic if he makes an unfair assessment because information is unavailable due to the disinterest or secrecy of those concerned.”

Holgate offered several ways a critic could evaluate a structure:

• Does it transmit its loads with economy and elegance?


• Is the structure efficient or ‘truthful’ (as opposed to deceptive)?


• How well does it address functional requirements e.g. those determined by an architect?

He suggested further questions that allow a balance to be struck between subjective and objective judgement:

"To what extent has the team succeeded in balancing the conflicts between the various objectives? In particular, how far has the structural engineer compromised the aims of the others? To what extent has he distorted the structure to accommodate the other requirements, and how far was this unavoidable?

"Has the engineer … by a brilliant stroke of creativity, devised an original form which improves the degree of fit on all fronts simultaneously over that achieved in conventional solutions to the problem? Has he suggested a complete redefinition of the problem which is satisfactory to all parties and permits a simple, elegant solution?"

Discussing the tension between a critic’s preconceptions and their inevitably subjective reaction to any structure, Holgate concluded that:

"in a field as complex as structural design there can be no single, simple prescription for design or criticism … The wisest commentators on the philosophy of design might be those who will take the discussion to a certain point, and beyond that realize that they have to leave the individual to react in accordance with his own instinct."

I think The Art in Structural Design remains extremely valuable. The book was aimed at engineering students to counteract the impression they often receive that engineering design is all about calculation and rational analysis. In addition to his attempt to single-handedly inspire a new field of structural engineering criticism, he includes interesting chapters on the process of creative design and the philosophy of structural design.

But more than two decades on, little has happened to make criticism of this sort a reality. Technical papers routinely receive little or no published discussion, even where the bridge presented is ripe for some pithy comment. There's no shortage of criticism that goes on in private, so I think there must be some way to bring it out into the open and see whether feedback on design quality can improve the general quality of product provided to clients.

One option is to create more spaces for views to be expressed: blogs like this one, or online forums like skyscrapercity.com, and to encourage knowledgeable engineers to participate.

Clients often take the lead in changing the culture of the engineering community, and should be less afraid to expose designs to public and expert comment.

Another way forward is to start at square one, and encourage future engineers to have a more holistic education, to hold opinions, and to gain confidence in expressing them. There are very few publicly visible, articulate structural engineers (certainly compared to the architects we collaborate with), and we need to cultivate more of them, so that structural engineering considerations can begin to be heard amidst the wider cultural chitter-chatter on architectural matters.

In future posts, I'll cover in more detail some examples of where useful published criticism of bridge designs has actually been made; how it is actually being cultivated today in engineering education; and also perhaps look at some of the prescriptions for aesthetic evaluation of bridges that have been made in the past by engineers such as Fritz Leonhardt.

[*The image relating to Brunel and Telford is from Eugene Byrne and Simon Gurr's Isambard Kingdom Brunel: A Graphic Biography]

Bridge criticism 2: No disparaging please, we're engineers

In a previous post, I noted that bridge design competitions often throw up designs that are uneconomic, unmaintainable and in some cases even structurally unfeasible. Yet there is a surprising lack of visible criticism of such designs: engineers generally like to keep their heads below the parapet.

One reason for this might be that engineers are ethically constrained, separate from their nervousness of the legal and commercial consequences. Do the professional bodies encourage or discourage open criticism of our peers?

In the UK, the Institution of Civil Engineers’ code of professional conduct [DOC] asks that:

“When commenting on another person’s work, members must advise that person of their involvement … members must not act maliciously or recklessly … members should take account of the broader public interest”

The ICE don't appear to contemplate the possibility of comment in journalism (let alone a blog!), where to contact everyone before commenting on their work would be a little over-the-top. But it's clearly only fair that those criticised should have a right of reply.

The ICE code draws upon the Royal Academy of Engineering’s Statement of Ethical Principles [PDF], which says that:

“Professional engineers … should be alert to the ways in which their work might affect others and duly respect the rights and reputations of other parties … Professional engineers … should uphold the reputation, standing and dignity of the profession”

That seems to put a somewhat old-fashioned notion of professional dignity above the rights of the public or wider community. Surely there are public interest issues which outweigh the rights of engineers to stand aloft from the fray?

IABSE’s Ethical Principles are considerably more specific:

“Members shall not disparage other engineers or scientists … Constructive criticism should be regarded as contributing to integrity and truthfulness”

Although the IABSE is against disparagement, it makes clear that constructive criticism is acceptable and may contribute both to the public interest and to the profession’s integrity. Indeed, it could be argued that criticism of a particularly poor design has the effect desired by the Royal Academy of upholding the profession’s reputation, by discouraging unworkable and absurd designs.

Personally, I think the public interest has to come first. If a design deserves criticism, it should receive it. The public (and, it seems, many clients) have no way to judge the engineering merits of structural engineering proposals, and it must be the case that better, more open public debate on these matters will ultimately lead to procurement of higher quality designs, and fewer cases of project failure.

Bridge criticism 1: Of heads, and parapets

Late last year, I attended a talk by architect Cezary Bednarski, which ran through his experiences in the bridge design competition arena. I've covered some of the issues raised previously, but there's one that I wanted to return to.

A topic that arose repeatedly related to the various occasions when Bednarski had lost a competition and lost it to a design which in his view was a very poor choice. He offered as examples the notorious Krakow footbridge (pictured left, click any image for a larger version), Glasgow, and a competition for temporary bridges in Rome. Other examples of bizarre competition winners include Cambridgeshire Landmark East and River Wear. These mostly offer examples of exotic, ambitious designs where their very structural feasibility should have been in doubt from the start.

There has been ample criticism both of a competition process which frequently delivers designs beyond the budgetary constraints of a project's promoter (e.g. Stratford-upon-Avon, pictured right), or which will saddle them with expensive maintenance costs for years to come (e.g. Trinity Footbridge). But where precisely does the fault lie? With the competition clients, organisers, jurors or the entrants? I actually think at least some of the fault lies elsewhere.

Several of these competition designs were criticised in the press after the winner was announced. However, in most cases serious criticism only appeared after the project had failed (e.g. when the Glasgow bridge scheme, pictured left, went massively over budget). Is there perhaps a failure of the bridge design community as a whole to speak up about designs which are likely to be unusually challenging or high risk?

For several of the competitions mentioned above, there was no specialist landmark bridge engineer involved on the jury, and it is possible that whoever did judge them had no realistic way of benchmarking the likely costs and risks of the designs put in front of them. In many cases, the shortlisted entries are not made public, so there is no possibility for anyone else to assist by making informed comment.

If there's an appropriately knowledgeable and empowered bridge specialist involved in the judging, then in theory the absence of wider input should not matter. But I still wonder whether competitions would benefit generally from greater transparency, and the opportunity for a promoter to receive wider comment on the merits of the entries. One of the aims of this blog is to see whether a space exists for constructive public criticism of the merits of bridge designs.

Of course, that's where the problems begin. The heads, and parapets, of this post's title, and the unwillingness of bridge designers to stick the former above the latter.

Criticism of others' designs is far more common in the architectural field, indeed it's something that's positively encouraged from an early stage through the use of the architectural crit as part of an architect's education. There are very few analogues in structural engineering, although I'll address some that do exist in a future post.

Engineers are traditionally reluctant to publicly criticise the work of their peers. There are several reasons: simple politeness, commercial pressures, legal constraints, etc. All three of these can be found at work here on the Happy Pontist whenever comment is made on the merits of a particular bridge design. Legally, there is the risk of committing libel if criticism goes too far. Commercially, the critic can upset someone who may otherwise be a future client or commercial partner.

In a follow-up post, I'll look in more detail at one: ethics. Could it actually be unethical to criticise designs? That might seem ridiculous, but the engineering institutions promote precisely that view.