25 September 2009

St Patrick's Island Bridge Competition entries: Part 1

I'm late to the party on this competition, which has been discussed extensively already at the Accelerated Bridge Construction blog and on SkyscraperPage (here and here).

Readers may recall that Calgary's Municipal Land Corporation (CMLC) has been running an open design competition for a CAN$25m footbridge across the Bow River to St Patrick's Island. Images of the submitted designs have recently been made available to the public online, and further details will be on show in October as part of the public consultation.

The contest follows the controversial direct appointment of Santiago Calatrava for another footbridge elsewhere on the river, and it's clearly of interest to see whether the competition format can secure a bridge that is either more impressive, or at the very least not as grossly inefficient structurally.

In a previous post about the St Patrick's Island competition, I predicted the following:

  1. Calatrava will not enter.
  2. There will be at least 100 entries.
  3. At least two shortlisted entries will be from locals.
Well, getting two out of three right isn't too bad. There were a mere 33 entries (2 submissions were disqualified), which I find quite surprising given both the recession and the history of similar open competitions across the Atlantic in the UK. Compared with the British contests, Calgary secured far more entries from serious, big-name designers, and far less from amateurs and student hopefuls, and that's despite the absence of any prequalification hurdle and any information which might allow commercial firms to judge their chance of success (e.g. judging criteria).

I'd normally argue that it's quite unfair to try and evaluate these designs without seeing the technical information that was also submitted, but, heh, why miss out on the fun?

After all, much of the criticism so far available online is driven by the architecture-as-porn mentality (an addiction to ever more outlandish novelty; over-stimulation leading to premature excitement; appealing to lurid or sensational instincts; the seductive lure of high resolution imagery). This tends to focus on the purely visual elements, and to ignore some of the functional and practical issues of more interest to those of us with actual involvement in the activity in question, in this case, designing and building a bridge.

It surely can't hurt to consider properly some of the engineering essential to any bridge design, especially this one.

So here goes: the competition entries, and a few thoughts on their merits. As always, click on any image for a larger version. Numerical order, incidentally, and I haven't provided links to the full PDFs (with more images), as you can find those at the CMLC website, for now at least.

Rosales + Partners / Schlaich Bergermann / et al

With this, two decks curved in plan each supported from a curved, inclined mast (offset in plan from the deck), Rosales seems on a quest to beat Calatrava at his own game. Yet even Calatrava has rarely attempted a structure as audaciously ill-balanced as this.

Visually, it's spectacular, with the asymmetry of the two masts working particularly well. Although access to the island is very much an afterthought, it is one of the few designs to properly respect the freeboard constraints given in the competition brief (basically, no structure should be placed below the freeboard level within the waterway width). It's also much simpler to build and maintain than many entries.

I have to admit, I'm puzzled as to what SBP are up to: an engineer renowned for their fantastic bridge designs drive by a strong structural engineering ethic, who seem now to be just a gun-for-hire in the service of increasingly extravagant architectural visions. Everything about the design maximises the bending in the masts, whereas only a few small cables tying the two together would be far more efficient, also reducing greatly the extent of the foundations required (which would be enormous for this design).

Design Vision

Roundly dismissed by the SkyscraperPagers for its amateur presentation, which is a shame. It has a sustainable element (solar panel roof), avoids infringing the waterway freeboard, is highly distinctive, and goes against most modernist commandments. It's nice to see something contrary, and while I don't like the design at all, I think it's a shame people have been so seduced by the falsities of computer rendering that they sneer at anything else. More crayons in bridge competitions please!

Manu Chugh / ISL

Relatively straightforward to build and maintain, although arches arising through the deck run the risk of attracting unauthorised climbers - ugly security measures could be required unless a "steeple-coping" cross-section is used (not what's currently shown). I like the idea of introducing a more meandering path onto the island, but think a lot more could have been made of that element.

Zhihi You

Like Manu Chugh, one of the local entrants, albeit with a very awkward design that clearly has little chance of success. From the engineering perspective, the arches could be made stable with far less cluttering, also greatly reducing the maintenance liability of so much intricate painted steel.

Rogers Stirk Harbour / Halcrow Yolles

Now here's one I really like. I've thought previously about the opportunities to take the traditional covered bridge and place a modern glass-roofed slant on it. Here, the sides of the bridge are as open as possible, achieved by suspending the deck on slender cables from a truss structure which sits inside the roof. The truss is shaped broadly in line with the bending moments it needs to carry.

It sits above the specified freeboard, and would be easy to build (although difficult to maintain, with all that raised glazing in close proximity to painted steel). Counting against it are the inexplicable slits in the roof (why?), and the lack of a well integrated pathway onto the island (from the images, it's not even clear if there is one).

Buckland and Taylor / Kitchell

It's good to see something essentially structural in conception, without feeling the need to hide its inadequacies in architectural frippery (a tendency beloved of building architects who in some cases have an ingrained habit of relying on cladding for effect). It would be nice to see people getting away from Calatrava's trademark white though.

This is a relatively straightforward bridge to build and maintain, with probably one of the best responses to the freeboard issue, keeping the island access out of the way of floods and ice flows, as well as the main deck. The flurry of backstays onto the island look over-engineered to me - sure, there's a need to visually match the number of cables used on the main spans, but it doesn't really need that many cables for balance. A cranked mast might have added interest.

Brett Lowe

Although the designer makes reference to native Indian traditions, and to the solar solstices, my main thought on seeing this one was that the Illuminati are clearly seeking to establish their presence in Calgary.

The structural design is entirely secondary to the idea of a vast pyramid high over the water, with a somewhat bizarre truss design incorporating irrelevant curved members, and which I have to say would really struggle to carry the wind loads borne by the pyramid.

Erin Swift

Despite the somewhat amateur execution, this design has some things to admire as well as to dislike. I like the idea of the bridge incorporating multiple pavilions, offering a less linear experience and taking advantage of the project's generous budget. To me, the variety is better than an all-exposed or all-covered bridge. However, the cable-stay pylons couldn't work as shown, with hugely eccentric loading and no balancing stays, and there are simply too many pylons within the river area, vulnerable to ice/flood damage and requiring difficult foundations to be built mid-river.

Ok, that's 8 down, so that will do for now, I'll continue in another post early next week. It's probably worth noting now, however, that I'm not expecting my views to be shared by CMLC - they have to balance the interest of the public and potential developers, and my experience is that the public's idea of a good bridge is quite different from a specialist bridge engineer's idea!

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1 comment:

lamkin said...

I am quite a fan for footbridges designed by SBP, but this time, I was a bit of disappointed. I remember Schlaich did mentioned that Structural Engineer should not downgrade themselves become a structural analyst but for this entry and in my opinion, Rosales maybe leading the concept design.