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 ...