St Patrick's Island Bridge Competition entries: Part 5

Right, this will hopefully be the last post on the Calgary footbridge contest for now; I'm sure everyone's heard more than enough about it by now!

The competition's client, Calgary Municipal Land Corporation (CMLC), say they plan at the end of October to shortlist an unknown number of entrants to go forward to the competition's next stage. Each of the shortlisted designers will receive a "modest stipend" to develop their design further (whatever that is).

So who would I shortlist? In no particular order (links are provided to the CMLC site as well as my own reviews):

• Rogers Stirk Harbour / Halcrow Yolles (THP / CMLC)
• Busby Perkins and Will / Fast and Epp (THP / CMLC)
• Arup / Falco Schmitt (THP / CMLC)
• Read Jones Christoffersen et al (THP / CMLC)
• RFR / Halsall (THP / CMLC)
• Erhard Kargel / Abes Wagner (THP / CMLC)

Some of those have their problems, but the first stage should be to select interesting and appropriate concepts, the second stage of the contest gives scope to see if each team can address them satisfactorily.

Who do I think will actually get shortlisted?

• Rogers Stirk Harbour / Halcrow Yolles (THP / CMLC)
• Infinity Engineering (THP / CMLC)
• SPF:a / Arup (Glide) (THP / CMLC)
• Marc Boutin (THP / CMLC)
• Halcrow Yolles (The Reach) (THP / CMLC)
• Read Jones Christoffersen et al (THP / CMLC)

Why the difference? I think public opinion will play a large part, which will get in one of the ideas that has little real structural logic to it (either The Reach, or the similar Arup / Kasian design). This will be balanced against the need for the design to be attractive to potential East Village developers, which will favour the inappropriately spectacular (this may of course be the same thing).

I also think they'll try and get through some of the interesting but flawed entries (Glide and the Infinity Engineering one) to see if the design teams can put right the flaws at the next stage. I think they'll want a few safe pairs of hands in there (Rogers, Arup etc). And I'd be surprised if there's no local firm on the shortlist, which puts the Marc Boutin, The Reach, Read Jones Christofferson and the various Halcrow Yolles entries in with a good chance.

How has the competition compared to other similar contests? For an open competition, I'm really surprised how few amateur or student entries have been attracted, and how many entries were submitted from really major architectural and engineering firms. If you compare pretty much any of the UK bridge design competitions with a similar open arrangement in recent years (Liverpool, River Douglas, Sheffield, Bootle, New Islington) the big names frequently shy away (due to the perceived poor ratio of cost to probability of success) and there's a lot of dross submitted. I'd be really interested in opinions as to why the Calgary contest has attracted such high-calibre talent - is it basically the CAN$25m budget, and the opportunities that creates?

How has it compared to the Peace Bridge appointment and design, a lurid red tubular truss which was sole-sourced to Santiago Calatrava? I think it compares very well - locals have had their fair chance (and no doubt learned a lot in the process of competing); public involvement is welcomed rather than shunned; a wide range of concepts have been generated possessing varying degrees of common sense and extravagance; and it has created a useful public forum for debate on design, which can hopefully only be good in raising awareness of the opportunities a signature bridge creates.

It hasn't been without its flaws: the competition rules and judging process remain entirely opaque and hence open to manipulation; and the public involvement is perhaps misjudged (how many online commenters are actually from Calgary, and how many are influenced by being able to see previous comments?)

But by far the major improvement over the Peace Bridge saga is the openness to competition, the acceptance that quality design doesn't have to come from the only name anyone's heard of, any more than every film must be directed by Stephen Spielberg. For that at least, well done Calgary.

St Patrick's Island Bridge Competition entries: Part 4

Ok, here is the final batch of my mini-reviews of bridges entered into the Calgary bridge design competition. Parts 1, 2 and 3 are also available, and part 1 has the proper introduction. Looking for more opinion? Accelerated Bridge Construction is posting a series of video reviews on Youtube, which I think are particularly clear and helpful for the general public without specific bridge engineering knowledge. And the public comments on the designs can be found online at the competition website, along with more images and details of each submission.

Infinity Engineering

This is without doubt one of the most ambitious, striking and unusual designs in the competition (or indeed in any of several recent competitions). Three curved bridges are supported via cable nets from a central mast, giving options to access the island or bypass it entirely. As rendered, it looks like the two island bridges would fall foul of the freeboard constraint and be vulnerable to ice damage, but that's something that could be changed easily enough. It's hard to tell quite what the pedestrian experience would be, as the emphasis is very much on icon rather than intimacy.

Is it buildable? Well, it would be unique for a bridge, but certainly within current technological capability. Cable nets are difficult to design, to assemble, and to stress properly, something that would be made more difficult on this design because the lower edge is fixed to the bridge deck, which would be a more rigid element. Again, that could be changed by introducing an intermediate edge cable along the bottom. The only existing cable net bridge which comes to mind is Schlaich Bergermann's Löwentor footbridge in Stuttgart, although that's a very different design. For the Infinity Bridge concept, I think they're hoping that the cable mesh can stiffen the bridge deck in a way that conventional suspension bridge hangers can't (for this is basically just three very fancy suspension bridges strung together). I'm unconvinced about that, but I'm no cable net expert.

The two shorter spans will be inherently stable, but the main span looks like a huge challenge to design - at this length, torsion in the deck will be very difficult to carry, without the advantage of a counterbalancing inclined element (although again, there are ways of addressing that). It's also far from clear that the cable-net on that span is in the right form, looking convex rather than concave in some of the images. A few days with some form-finding software would sort that out.

My main dislike of the design comes from considering it in operation. It will be a very difficult structure to maintain - replacement of a suspension hanger is relatively straightforward in a conventional suspension bridge design, but replacing cable net elements is far harder. There's also the entirely predictable likelihood of unwanted climbers making it their playground.

I'm also less than keen on the gargantuan scale, which seems completely out of place given the rest of the surrounding landscape.

RFR / Halsall

RFR's design is one of the simpler, more elegant solutions, with a series of slender arches seeking to minimise impact on views on or off the bridge. While it looks far too skinny to survive the crushing impact of an iced-up river, it's straightforward to build and maintain, and should leave plenty of spare change in the CAN$25m budget. That will come in handy for the actual walkway connection down on to St Patrick's Island, which seems to have been largely ignored in the competition images.

It reminds me somewhat of the Pont des Arts in Paris (where RFR are based) in its delicate elegance.

Saucier Perrotte

Three glazed tubes enclosing a steel space truss. All the emphasis here is on what can be done with the glass - fritting to provide a varied visual texture (darker at the ends, lighter in the middle), and lighting inside, with the aim being to provide something that is continually varying.

What else can be done with glass? Scratching it, painting it, breaking it all come to mind. I'm not sure suitably laminated and toughened glass can be formed to these tight curves, although again that's not my area of expertise.

I'm not a fan of this one. The structure will need to be more obtrusive than is suggested, it's too much like a tunnel, and the tubular form is just too straight, particularly viewed in elevation - there's nothing to express the leap that a bridge makes from ground to ground, this would work better as an elevated walkway in an airport, a more highly policed environment.

SPF:a / Arup (O-Bar)

The first of two entries by this team. It's easy to see how this is a love-it-or-hate-it-design, with its monolithic, rust-covered monumentality. I actually quite like it, although I can't think of many settings I'd like to see it in, including this one.

The bridge basically consists of two oversized box girders made of weathering steel, making it one of the very few steel designs to have considered the need to minimise maintenance costs (although in this close proximity to pedestrians thought needs to be given to its vulnerability to graffiti, and the need to ensure hands and clothing can't come into contact with all that rust). The girders are far larger than they need to be, even though they have an undulating shape which reflects the intensity of bending moment at any point (very nicely widening out where the girder is in compression and hence needs to be wider to give stability against lateral buckling). I like that.

Its nicely rendered, although some of the images omit the tie bars from top to bottom girder which would surely be needed across the window slot. There's also an entirely fanciful image of how it could be built out of interlocking modules, which would be a horrendous way to put it together, with the huge number of full-strength butt welds required.

Against it? Well, the way it blots out most views up and down river; the somewhat claustrophobic feel; and the imposing mass amidst the tree-lined Island (although the contrast is interesting). Contrariness is always welcome, but it will never win this competition.

Arup / Frederic Schwartz

Not a bad design, a single masted cable-stay bridge which ticks all the key boxes for buildability, maintainability and minimal ecological impact, but which is generally a bit lacking in inspiration. Bending moments on the mast due to asymmetric loading will be significant, but not unconquerable. The mast could do more to accentuate a needle-like shape, I think, and I think the curved path down to the island is much less attractive than several other entries.

Bosen Lu

I've stared at this design for a long time and still don't really understand how it's intended to work structurally. The plan and some of the other views imply that the cable plane is central to the deck, but some views imply the cables are connected to herring-bone struts protruding laterally from the main mast. It's far from clear whether it's properly back-stayed, with some views suggesting that it's stayed onto the back-span, but not to ground, which would be an unusual choice for an asymmetric cable-stay bridge. I don't feel able to judge it in engineering terms, so can only comment that to me, visually it is over-fussy and out of scale with the context.

Erhard Kargel / ABES Wagner

This is an interesting design, but certainly not a great one. The basic structure is a nice idea - a single masted suspension bridge, with the two spans at an angle from each other so that the mast needs further cables onto the island to restrain it. These cables are then used to support the island walkway. The mast-head cable connection detail will be a challenge, but it's otherwise an elegant, pleasant bridge design.

What lets it down is the lack of attention to detail, particularly at pedestrian level. It's a sketch rather than a finished design (not that this is necessarily a bad thing given the tendency of open competitions to attract ever more preposterously rendered imaginings). It's almost impossible to figure out how well the bridge will relate to its arboreal context, but to me the mast looks far too tall.

SPF:a / Arup (Glide)

That's how many entries from Arup? I make it five, which must be some kind of a record for any bridge design contest, surely. Well done!

As with the other SPF:a / Arup entry, this is easily one of the more radical concepts, visually if not structurally. A precast concrete box-girder deck is supported on steel struts (the edge members are described as tension members although presumably they'd be in compression next to the island - unless it spans the island too, which seems unlikely). The soffit is hidden by zinc cladding. The balustrades are of structural glass, which looks nice when rendered but will be terrible to maintain in this environment.

Picking the flaws first, it interferes enormously with the stated freeboard constraints, and is therefore likely to be a no-go because of its massive impact on river hydraulics during flood conditions. And while the stepped ramps look nice on paper, there would be no usable access to the island when floods occur. The structural form is somewhat dubious in its behaviour - if the outrigger chords are intended to act as the tension member of a deep beam, then how is longitudinal shear transferred? And almost no thought seems to have been given to what the space would be like beneath the structure.

In its favour, it sees the bridge as a public gathering space rather than a point-to-point walkway, and it easily achieves landmark status without the paraphernalia of towers and cables. But I can't see how these can overcome its many problems.

In the next post I'll put together some predictions for the shortlist. I'll also see if there's anything to be said about how the competition has compared both with other design contests, and with Calgary's recent appointment of Calatrava for his Peace Bridge design.

St Patrick's Island Bridge Competition entries: Part 3

Onwards, onwards, before I either wear out my typing fingers or, more likely, just get plain bored.

This is the third of four posts reviewing the entries to Calgary's contest for a new CAN$25m footbridge. Go to their website for a proper set of images and text describing each design (or just to gawp at the public comments). The first of the previous two posts in this set has the proper introduction, so without more delay ...

Delcan / du Toit Allsopp Hillier

This is the only one so far I've included three images for, and that's just because the Christmas card view is so lovely.

At first glance, this looks like a hundred other footbridges with curved decks slung from inclined arches, but on a closer look it is clearly different, and indeed puzzling. The plan layout is simple and very attractive, with plenty of scope for landscaping on the island, but the first puzzle is the presence of lattice cables tying together arches which clearly have no structural need for them. If you're going to create network arches, why bother with the "vertical" hangers, and vice versa? It's really the cables that are odd, because the stiff "hangers" may be required to stablise the deck.

And it's that thought of deck stability that really confused me when I gave it another look. On the majority of this type of bridge, the arch inclines in the opposite direction from the deck curve, so that the two both counterbalance and brace each other (see for example the Sturgess design below). Even then, the deck requires substantial torsional stiffness to work. But here, both spans have the arch on the outside edge of the curve, and inclining still further out. That puts a far, far greater torsion on the deck, which would have to work exceptionally hard not to have vibrational problems, and the arch becomes far less efficient because both arch and deck tend to buckle together. I'm sure you could just throw money at it until it stands up, but it's a fundamentally flawed concept.

IBI Group / ipv Delft/ Williams Engineering Canada Inc. / et al

Without a doubt this would be the biggest "landmark" of any proposal, a 180m span arch that doesn't touch the island at all, except for a little walkway. We're not told if it's a bowstring or not, but it's rendered as a thrust arch, which would require some quite spectacular foundations, even though the depth to bedrock is not great. The deck is offset from the arch, so there's a reasonable lateral bending load on the arch to transmit to ground.

While they make a virtue of the lack of impact on the island, they don't really address the huge impact of construction, all the temporary propping or tie-backs that would be required. And the bridge's biggest problem is simply that not enough attention has been given to the details of the design, particularly the shaping of the arch in cross-section.

Sturgess Architecture / Halcrow Yolles / IBI Group / et al

Compare this one to the Delcan design above. The designers for this one say: "A unique feature of the bridge is that its structural efficiency and delicate ribbon arches are achieved by counterbalancing the forces of the arch and pathways". Of course, it's nothing like unique, designs which balance like this are ten-a-penny, but what makes the Sturgess bridge different is simply the way the pedestrian and cycle routes are structurally separated.

While I'm in favour in principle of separating the two, I think in this case the structure just gets over-complicated and over-heavy, with the raised struts between the two somewhat unsatisfactory. The Gateshead Millennium Bridge did it better.

CH2M Hill / LeBlond Partnership Option #2

Ah, it's a relief to see something that's understated, elegant, and consciously trying to avoid undue flamboyance. Two very shallow arches are proposed here, with the aim of putting the emphasis on the Island and not on the structures. It's a thoroughly admirable sentiment, and it's a shame the single image doesn't really do it justice. But it won't win.

CH2M Hill / LeBlond Partnership Option #1

Meh. It's not bad, it's just dull. There's just so much more that can be done even with such a default cable-stay iption. Sure, it ticks the boxes - reasonably straightforward to design and maintain, and it keeps out of the river freeboard. It's the pylon I particularly dislike. The designers call it the "needle". I call it a grey carrot.

Endres Ware / Ammann & Whitney

While it's nice to see several entries which have a clear structural rationale, it's disappointing that few of them go the extra few yards that would really make them special. Where a bridge design is engineer-led, with the architect subsidiary, it's vital that the architect's attention to detail, to the bridge's intimate experience, is used to really step up the quality, and there's little sign of that here. Sure, the cables are where they should be, and the pylons are nicely arched, but overall it's just far too busy, and the island pathway is poorly layed out. It seems out of place and out of scale to the island.

Arup / Kasian

Ordinarily, I'm a great rollercoaster enthusiast, but I somehow don't think there will be a runaway mine train rattling over the crests of this bridge. As with another design, this one is partly inspired by fly-fishing - could someone tell me what precisely is wrong with a bridge design inspired by "getting across the river"?

If I understand it correctly, it's a relatively conventional bowstring arch bridge, with two arches on the long span and one on the short. Plus a gigantic squiggle of metal pipe that's mainly there to confuse the issue and hence make it "hip" (does anyone still say that?). It's irrational, effervescent, and sadly just a little too confusing to have any logo appeal. I think I'm mostly neutral on it - structurally, it's completely daft, but some city somewhere should have the right to wave a big flag about how postmodern and ironic they are. I'm not sure Calgary is the right place, nor that it shows any consideration for the river-and-island context.

Team IBHL

I have to admit I did think for a second about just photocopying Calatrava's Peace Bridge design and submitting that as an entry, just for a laugh.

I do hope this fashion for helical tube bridges doesn't last long, it's a deeply inefficient concept and very limited in how it can be applied well visually (as witnessed on the very poor end treament for this one).

In their favour, they've pushed the helical members closer together than the Calatrava bridge, making it a bit more affordable, and made great play of how it can be built with locally available steel (Calatrava's bridge is likely to be fabricated by Cimolai in Italy). It is at least curved in plan, which makes the helical truss choice slightly more pardonable than Calatrava's. Against it, setting aside the inevitable accusation of plagiarism, there's an entirely superfluous concrete box inside it, and too little thought given to the island landing. Like the Peace Bridge, it will be a bugger to maintain as well, with all that intricate steelwork, some of it in too-close proximity to the concrete box.

Read Jones Christoffersen / Riddell Kurczaba / Simpson Roberts / et al

I thought for a moment I'd get to the end of today's batch without liking a single design, so I'm glad to finish on this one. It may not be entirely clear from the images I've picked, but this bridge has two opposing suspension spans, presumably not self-anchored due to the high deck curvature. There are no back-stays on the masts, which therefore carry the main cable loads in pure bending, assisted at least a little by being inclined backwards (in contrast to at least one of the other submissions). The foundations will therefore be on the large side, but the two masts will to some extent balance each other out under normal load conditions, so it's not quite as bad as it may seem.

It respects the freeboard limitations, the path to the island is complemented with a nicely cantilevered viewing platform, and it's relatively straightforward to maintain, notwithstanding the many corrosion problems for which suspension bridges are notorious (likely to be easier to solve with the cable sizes required here). It will be a real challenge to build, mainly because of the very shallow trajectory for the main cable. At that angle, the support to the deck is very limited, and there will be significant changes in cable shape as the structure is built piece-by-piece. Lots of careful adjustments in cable tension throughout construction may be required.

It's also nice to see a design that in some way echoes the suspension bridge which is already there, which achieves landmark status without getting too ridiculously out of scale, and which is driven primarily by the inter-relationship of its geometrical and structural form. Even better, the initial public comments seem to agree, so it would be no surprise to see this one on the final shortlist.

Ok, that's it again, for now, I'll return with the final set of designs when I get a moment.

St Patrick's Island Bridge Competition entries: Part 2

Right, let's have a run through the next batch of entries to the Calgary bridge design competition ... Again, you can find more detail on each design at the CMLC website, where they've now replaced the PDFs with web pages (shame, because it means you can't zoom the images to a larger scale), where people can also now comment freely on each entry (although I think it's a mistake that the comments are visible publicly, that's bound to inhibit some responses).

What's that, no idea what I'm on about? See the previous post for a proper introduction.

Busby Perkins and Will / Fast and Epp

A slightly odd one. There are features to dislike such as the seeming impossibility of designing anything Calatravaesque in any colour other than white. The uneven cable arrangements are also peculiar - why not just have the same number of cables on either side of each mast, however asymmetric the spans supported (the masts don't look to be sized for the out-of-balance moments that will result)? And why not back-stay the towers (although the offset deck loading is nowhere near as pronounced as at Calatrava's Sundial Bridge)?

Regular readers might expect me to be unimpressed by the staggering expense that will result from supporting both deck and masts on prong-like cantilevers - the foundations would be enormous as would the amount of island despoiled to construct them. But I really like that feature - I like the way the bridge stands off the island, and the way the masts are shaped. If you're going to spend CAN$25m on a bridge that clearly doesn't require it, this is an ambitious way to do it.

Marc Boutin / Williams

Here, the landmark and the bridge are separated, with a solar-powered lighting tower just off the main bridge structure, which comprises a pair of arch-supported stressed ribbons. It's feasible structurally and likely to be low maintenance, although it has to be pushed quite high in the air to meet the contest's freeboard stipulations. Good use is made of the arch/ribbon geometry to create alternative pathways, but there's still something not quite right about it to my mind - perhaps it just lloks like it could be a little too bleak and windswept, pictures of smiling bathers notwithstanding.

Associated Engineering #1

This is a real oddity. It's a cable-stayed bridge with the cables tied to a pair of inclined arches on the island, the form of which has been inspired by a buffalo skeleton, with bracing intended to evoke stretched animal hides. I was glad to read that, because until I did it just looked utterly baffling, and not a little disconcerting.

Visually, I think it's over-complicated and geometrically confusing, something that would also be reflected in high maintenance costs when repainting falls due. The animal-hide bracing is overkill from a structural point of view, and while it would be both iconic and a landmark, it seems to entirely lack the finesse that the better-architected solutions have.

Associated Engineering #2

This one throws together several interesting ideas, none of them having much to do with the bridge itself, which is almost an afterthought. The spans are drawn as very slender line beams, certainly more slender than would be feasible given that they have to carry both the deck and a row of cupola-like offset pods, each of which features a glass floor, and a set of "resort style muskoka chairs ... provided for optimum comfort with cup holders in the arms". There's yet another solar tower, a public plaza on the island with an artificial beach and artifical campfire, and a pavilion (which I expect is where the inevitable kitchen sink resides).

While the frustrated architect rejoices at the focus on the site as a space for social activity, the maintenance engineer winces at the opportunities for vandalism, muggers' hideaways, and general mischief. It seems to be trying too hard, and isn't well enough detailed or engineered to stack up against some of the competition.

Arup / Falco Schmitt

Here's the second of today's paired stress-ribbon bridges supported on arches (a concept very rarely built but which may be in vogue, perhaps). Arup, of course, won the River Douglas bridge design competition last year with a very similar design (down to the steel arches and even some of the buzzwords included in the submission). When the rest of the world is obsessed with novelty, it's good to see ideas being recycled. High marks for sustainability, I should think.

The ribbon sag doesn't initially look particularly feasible, but with 25 million bucks, these short spans, and a bit of optical illusion in the deck shaping, it probably is quite achievable. The design is elegant and hence admirable, although it may be Calgary will want something with a bit more razzmatazz to help give developers the icon for the East Village development that they'd presumably like. Marks off for having the arch legs within the river freeboard, perhaps, but otherwise it's a buildable and low-maintenance solution.

De Jong / KTA

Another design with some good and some bad points. Chief among the former is the plan layout, which is very attractive, and the conscious decision to retain trees close to the bridge on the island, so it can be something of a treetop walk (at least until someone trains the squirrels to snatch handbags).

Set against that are the arches and cable layout, which I find quite unattractive, and the inattention to basic structural engineering, with two flaws that particularly leap out. The first is the exceptionally low cable elevation, which will hugely increase costs both due to the inefficient support to the deck (saggy cables with low vertical components of force) and also the massive compression forces and lateral bending induced in a curved deck (due to the high horizontal components of force). Match that with the very odd decision to tie the cables to sickle-curved struts above the walkway which couldn't possibly anchor the cable forces properly.

Halcrow Yolles - The Reach

It's good to know that "The Reach" is inspired by a fly-fisher's line cast, because otherwise it's hard to know what to make of this self-consciously freeform squiggle. Great logo potential, I'm sure, and an absolute bitch to build (and maintain, what with its glass balustrades). It reminds me in part of Giffords' Celtic Gateway footbridge at Holyhead.

I find it almost impossible to offer a sensible opinion, as they've only included one proper image of the bridge, and that remains unclear as to both how it works structurally, and how it might be experienced as a bridge user.

Halcrow Yolles - Eddy and Flow

The second Halcrow design eschews spectacle in favour of an organic, sculpted concrete form intended both to provide a variety of pathways and also to "express the actual structural forces that are in effect as the bridge makes its span".

From an engineering perspective, that statement is nonsense, as the form of the bridge determines the forces every bit as much as it expresses them. Nonetheless, a sculpted bridge has potential, as was recently illustrated in Dublin. As with many of the designs, this bridge impinges significantly on the freeboard limits, and its weighty appearance would at least lead to a low-maintenance solution.

Right, that's another batch out of the way. I'll return with more comments on the entries in a day or two's time ...