Bridge competition debris part 11: Leamouth

There have been several schemes to build new bridges at Leamouth in east London (where the River Lea joins the River Thames) over the years. One such scheme, held in 2003, and promoted by Leaside Regeneration, involved a design competition for an opening footbridge. This was to provide a link into the somewhat isolated and downtrodden Leamouth peninsula (shown on the right) and encourage new development.

Six entrants were initially shortlisted, and the winner was announced in July 2003 as Whitbybird.

Whitbybird's £3.5m winning design received planning permission in 2005, but funding was withdrawn later the same year, and the bridge was never built.

That design would have been spectacular and unusual if built - but also incredibly inefficient. In the closed position, it greatly resembles Santiago Calatrava's Puente del Alamillo, with a pylon which will carry substantial bending moments. As it opens, its weight is unbalanced at every stage, so the opening machinery has to be oversized, with higher running costs than a balanced design. Like the Gateshead Millennium Bridge, it would have been unique and expensive.

Of the other designs, both those from Price & Myers and Future Systems suffer from inaccessibility: steep approaches unsuitable for mobility-impaired users. They seem to be futuristic visions out of context to the site, creating technological challenges for their own sake rather than as a response to clear functional needs.

The Ian Ritchie design is a retractable bridge, an unusual opening variant often shunned because of the amount of space required on the river bank - although by overlapping that space with a permanent ramp, they have minimised the difficulty. Blue Office's inflatable truss would be the sort of thing to brighten the hearts of knife-wielding East-End vandals bent on puncturing architectural ambition.

The McDowell and Benedetti design is a swing bridge with an unfortunate lump and, I would guess, a problem inherent to the cable-stayed swing bridge whereby massive twists and inertias are generated during operation, as the cables provide no lateral stiffening to the supported deck.

As ever, links are only provided if a firm has project-specific information on their website. Click on the images for larger versions. I have only incomplete information on the competition, so if you are aware of any errors or omissions, send a comment.

Winner

Whitbybird / Rummey Design

Shortlist
Price & Myers / Niall McLaughlin

Strasky Husty and Partners / Future Systems

Ian Ritchie

Blue Office Architecture / Airlight

(more information on Tensairity beams is available online, see also the Airlight website)



Arup / McDowell Benedetti / Kenneth Grubb Associates

Now, this competition wasn't the only attempt to get a bridge built across the River Lea at Leamouth.

2002 had seen the end of the Peabody Trust's scheme for an inhabited bridge over the Lea, designed by Cartwright Pickard.

In 2004, while the Whitbybird design was being prepared for planning approval, Wilkinson Eyre and WSP were appointed to design a bridge elsewhere on the peninsula, part of a development by Ballymore. Like Whitbybird, this survived only two years, before receiving a bad review by CABE, and being dropped in favour of a design by Thomas Heatherwick.

I can't get my head round what went on with the Heatherwick design - the images available show an outlandish and impractical design with the deck supported on "ribbons" from adjacent buildings. But planning drawings dated March 2007 [PDF] and with WSP and Heatherwick's names on them show a far more conventional cable-stayed bridge with no support from the buildings. It was reported in 2008 that Heatherwick's design had in turn been dropped in favour of a more conventional solution by the wider scheme architect SOM, so perhaps the drawing shows that design. SOM's own images of the scheme on their website continue to show the Heatherwick proposal ... confusing!

In any event, the bridge remains unbuilt and is likely to remain that way while the credit crunch continues.

WSP / Wilkinson Eyre

Thomas Heatherwick

Thomas Heatherwick / WSP ... or is it SOM?

Updated 14 Feb 2011: added revised image of Ian Ritchie design, and amended accompanying text.

Waiwhakaiho Arch Bridge

Regular readers will know that the Happy Pontist concentrates on bridges news in the UK, and only occasionally ranges further afield. With that in mind, it's nice to be able to cover a proposed new footbridge from nearly as far afield as is possible: New Plymouth, in New Zealand.

In May last year, it was announced that New Plymouth's Coastal Walkway would receive a 4km extension, including a new 68.7m footbridge over the Waiwhakaiho River. The bridge, pictured above right, is being designed by local firm Novare Design, who have kindly sent me several preview images showing the design as a work-in-progress (i.e. there are quite a few details which are likely to change).

The unusual steel arch design won a design-and-build lump sum competition, with the designer estimating the cost at less than US$4,000 per square metre of deck. The site is important in Māori history, being a place where the tangata whenua resisted occupation of their land by the Pākehā in the late 1870s.

The bridge's bleached skeletal design owes a clear debt to Santiago Calatrava, albeit more organic in feel and less high-tech. That impression is in great part due to the way the arch hangers extend above the arch itself, making it hard to see the pairing as anything other than ribs and spine, the remains of some long extinct whale perhaps.

The arch passes over the deck diagonally, although the deck is supported on one edge only, which gives rise to the somewhat peculiar rib geometry, whereby the hangers have to curve increasingly towards one end of the deck.

Visually, I like the asymmetry that this introduces, although structurally it's far from efficient. The edge support will lead to a substantial torsion in the deck which has to be restrained at each end, while the angle and curvature of the hanger ribs creates both a tendency towards horizontal sway (like a swing suspended above its lowest point) and the need for the hangers to resist substantial bending moments. For a roughly 70m span, I'd guess all these effects remain within a reasonably economic range to be worth accommodating in a landmark footbridge.

The bridge behaves as a tied arch, although the large armatures at the ends of the arch spine give more of the impression of a thrust arch - I find this a little odd, but visually, it may look better than the "wedding-cake" approach sometimes favoured by Calatrava where the structure is poised precariously on supports of a very different form (e.g. Puente del Campo Volantin).

Overall, it's an attractive spin on a classic bridge form, tweaked sufficiently to be interesting, but not so far as to require extraordinary measures to maintain stability.

Commenting on the way the bridge was procured, the designer, Peter Mulqueen, notes:

"With regard to lump sum competitions for foot bridges, I think there always needs to be a set of vibration criteria explicitly outlined in the competition documents. The competition should allow for this level of preliminary design in its compensation to entrants. Otherwise one ends up competing against super skinny structures that do not have a hope of remaining stable under pedestrian and wind loads, but are very material efficient and often cheaper."

In the UK, footbrige design competitions normally involve a basic requirement that designs comply with current standards (which cover vibration), and are stable against lateral excitation in particular (the latter requirement being a legacy of the Millennium Bridge's wobble). However, it's unclear in how many cases competitors actually carry out these checks - often it depends on the risk-reward ratio inherent in the competition setup.

For open competitions where large numbers of entries might be expected, only a tiny fraction would bother to do any structural analysis at all, let alone derive predicted deck frequencies or accelerations. For invited competitions, most competent firms would carry out dynamics calculations, although in some cases (where the simple checks show a possible problem), the proposal will be made to use tuned mass dampers to deal with vibration, rather than to amend the form of structure to eliminate the problem.

In theory, design-and-build competitions like the Waiwhakaiho one should be ideal, as the risk of having to remedy any vibration problem falls on the contractor, who is likely to be extremely risk averse and insist their designer address it at the outset. Regardless, if it's going to be a concern for the client, they should be seeking assurances about the design right from the start.

Bridges news roundup

Is it a Burj or is it a bridge?
It looks like the seven-star Burj-al-Arab hotel - but no, it's actually a bridge (resemblance to Portsmouth's Spinnaker Tower may also be noted). This could be a great trend - who's first up for a bridge suspended from a leaning tower, Pisa-like?

ICE historic bridge awards
These were announced some time ago, but the newsletter of the ICE's Panel for Historic Engineering Works (PHEW) appeared more recently and included lots of detail on last year's winning schemes. The engineering ingenuity that goes into conserving historic structures is often far more challenging than that applied to new designs!

Indian rail bridge collapses during construction
Four killed in Bihar. In a somewhat bizarre follow-up, a lawyer claims the collapse was engineered as an assassination attempt.

Ice falls from Severn Bridges
Engineers scratch heads

Banff says no to fancy footbridge
Locals favour replacement of road bridge, but since it's a historically significant and structurally sound John Smeaton design, this seems extremely unlikely

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 competition debris part 10: Royal Victoria Dock

In 1995, the London Docklands Development Corporation held a competition to design a 200m long footbridge across the Royal Victoria Dock, connecting Silvertown on the south to the ExCel exhibition centre on the north. Central to the challenge was the need to maintain a substantial clearance to tall-masted ships, with the result that the bridge had to be at least 15m up in the air to allow for normal use. As a result, all the competition submissions are for a relatively unusual configuration of bridge.

The competition was won by Techniker and Lifschutz Davidson, with an innovative and undoubtedly spectacular 128m span "inverted Fink truss" bridge. Their design featured a 40-person transporter gondola at low level, so that pedestrians could cross the waterway without first having to use a lift or the stairs. Sadly for fans of transporter bridges, this element has never been installed, as foot traffic just doesn't justify it.

I greatly admire the attempt to rehabilitate an archaic railway bridge design (technically it's not really an inverted Fink truss as several diagonal ties are omitted - it's almost more of a variant cable-stayed bridge), and in elevation (see images below), the superstructure design is a very striking form. The supports are far less successful, especially the very monolithic enclosed stair and lift towers, and overall the scale is perhaps too much, it just towers too much above the surroundings.

The deck's extreme slenderness is also only maintained at the cost of somewhat unsightly bulges above walkway level, apparent on the photograph (above right), which also shows the use of external cables near the parapets for, err, unauthorised maintenance access.

Of the other competition entries, I find the Robert Benaim one somewhat baffling as it is not at height and is unclear how ships are allowed for - perhaps it's from an unrelated competition! The curved tie to which most of the stays are attached looks pretty but structurally all it adds is a huge problem if cables ever need to be replaced.

The Cezary Bednarski design seems the most successful at resolving the difficult end towers, something the Price & Myers proposal does very poorly. I like the Richard Horden submission, especially how it begs the question of whether an opening span would be a much better approach for a waterway which I imagine only rarely accommodates high-masted vessels.

I've tried to find images of the unsuccessful entries on the internet, but so far only found four. I don't know if there were more. If anyone can point out others to me, I'll update this post in the future.

As ever, links are only given if there's more information on a design on a firm's website. Click the images for a full-size version.

Winner

Techniker / Lifschutz Davidson

All three images courtesy of Liline Sur Flickr

Other competitors

Cezari Bednarski / Dewhurst Macfarlane

Richard Horden Associates

Powell Williams / Robert Benaim

Price & Myers / Eva Jiricna

Ian Ritchie / Arup

Updated 14 Feb 2011: Added image of Ian Ritchie / Arup entry.

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.