21 December 2011

Bridges news roundup

Moxon completes Taunton bridge
Modesty is a virtue (pictured - more images at Moxon's website).

Polyurethane/steel deck wins Canadian design award
Sandwich plate deck system used to minimise dead load in bridge refurbishment scheme.

Memorial Bridge Design Battle Just Beginning
Busybody seeks to add pointless frippery to New Hampshire bridge design.

New River Wear bridge in Sunderland given the go ahead
Government accepts arguments that "iconic" element of controversial design offers good value-for-money, finally securing the future for the new Wear bridge. This is something of a triumph for designers Stephen Spence and Techniker, who saw their initial design contest entry disappear into a black hole before it was eventually revived. Considerable effort has gone into making this bizarre design stand up, and I hope more details of the engineering become available in due course, through a technical paper perhaps.

Sturgess: An unusual process yields an extraordinary result: Peace Bridge
A quite extraordinary love letter to Calatrava's still incomplete Calgary footbridge.

Wow! That's one nice-looking bridge
The Calgary Herald calls it "iconic but overpriced". Get off the fence - was it worth it? A late January opening is currently anticipated.

Be’er Sheva  Pedestrian Footbridge
Winning proposal for yet another "iconic" project (pictured). Slightly reminiscent of the Gatwick Pier 6 passenger bridge.

Gateshead Millennium Bridge bollards to go

City of Toronto halts new Lovelocks fad on Humber River foot bridge
Joy-killing jobsworths hard at work in Toronto.

20 December 2011

London Bridges: 21. PaddingtonCentral Footbridge

This is the last of four footbridges that I visited in Paddington Basin, London. It is the furthest west of the group.

I will confess that what first attracted me to go and visit this bridge was a photo of it online showing the slightly unfortunate positioning of one of the main support legs - right in the middle of the access ramp! It has clearly been built on a very constrained site, but I'm at a loss as to why they couldn't avoid this.

The bridge design seems to pick up on several common features of a "modern" pedestrian bridge, throwing them together in a haphazard jumble that not only is unnecessary at this site, but would be so at any site. These design features aren't connected by the usual logic.

One feature is the use of cables to support the bridge on one edge. The pylon is connected to the deck with a series of cables, and is anchored by back-stays to the ground. At this sort of span, cable support isn't really necessary, and when you see the bridge from underneath, it appears doubly so.

The bridge is supported on Y-shaped steel frames at each end of the main span, and the main girder looks beefy enough to hold the entire deck up on its own. The cables introduce a horizontal force into the deck which must be resisted by the Y-shaped frames, emphasising the artificiality of the layout (the horizontal force is normally carried as a thrust in the deck directly back to ground). With this arrangement, supporting via vertical hangers from an arch would have made more structural sense.

The circular edge girder is positioned in such a way that there's no clear continuity between the access ramps and the main span's bridge deck. No doubt some of this ungainliness is a result of the constrained site, but I suspect more of it comes from trying to match the bridge's necessary geometry to an arbitrary and inappropriate choice of structural form.

In short, it's an object lesson in how not to design a footbridge, well worth visiting just to see what mistakes to avoid.

Further information:

13 December 2011

London Bridges: 20. Station Footbridge, Paddington

Proceeding west from the Rolling Bridge, I'll skip past a very dreary cable-stayed footbridge and move on to one that is a little more interesting.

Designed by Langlands and Bell with Atelier One, the main section of this footbridge is 44m long, with a 19.6m main span. The deck is 3.5m wide, and is suspended below a glass-clad steel "sail", 8.4m high. Langlands and Bell are artists (I think this may be their only bridge design?), not architects, specialising in an quixotic blend of styles which I would think of as pop-art-meets-minimalism. At Paddington, minimalism wins out - this is a bridge as if designed by Donald Judd.

The effect is quite unlike most footbridges. It's a proper gateway structure, proffering a letter-box entry to Paddington Basin from the west, and helping to hide an unattractive building when approached from the east.

Structurally, it is not especially complex. The walkway is a simple grillage of steel beams, suspended at midspan by a single hanger, with diagonals partially obscured by the glazed enclosure above. The form is an inverted king post truss, which is about as simple as it gets. The walkway cantilevers to either side of the support structure, supporting structural glass balustrades.

I think the glazed wall is visually very effective, particulary in images showing it illuminated at night. It's non-functional, in the sense meaningful to an engineer - it makes the structure harder to design, by adding enormously to the wind load, but the central cut-out prevents it from acting as a wind-screen. It allows for multiple alternate crossing experiences, and is boldly assertive but visually permeable.

Even visiting it on a dully grey day didn't harm it much. It helps distract from the dreary nature of the nearby building, and even from an adjacent construction site.

I like it.

Further information:

11 December 2011

London Bridges: 19. Rolling Bridge, Paddington

Heading west from the Helix Bridge, the next footbridge at Paddington Basin is the Rolling Bridge, easily the best known of the set, and justifiably so.

I would guess few of my readers will be unfamiliar with this bridge, as it is one of the most remarkable and audacious footbridge designs from the last decade. As with the Helix Bridge, it's something of a white elephant, spanning a very small side-arm of the canal, which goes nowhere and has no real reason for continued use by boats. The bridge is useful in providing a direct route along the edge of the main canal basin, but it doesn't really need to open.

Nonetheless, it does open, every Friday at noon. Sadly, I was there on a different day of the week. The opening mechanism is unique: the bridge slowly curls up from its level position, ending up in the form of an octagon when fully open. Its initial form, which broadly resembles a modified Warren truss, is distorted by extending eight hydraulic cylinders in each of the trusses.

Most moving bridges operate on the principles of translation (lifting and retractable bridges) or rotation (bascule and swing bridges). Very few adopt the principle of transformation, indeed about the only other examples which come to mind are Schlaich Bergermann's folding bridge at Kiel and arching bridge at Duisburg.

There is a sense that the Rolling Bridge's design is just a gimmick, but on balance I think not. It's delightfully inventive, playfully so, with the resemblance to a curling caterpillar responsible for a significant cuteness factor.

It was designed by Thomas Heatherwick, with structural engineering by Packman Lucas and SKM Anthony Hunt. The steelwork was fabricated by Littlehampton Welding. It cost £330,000 in 2004, which seems a lot for a 12m long bridge, but was surely worth it.

Up close, the detailing is nicely done, although the bumpy profile of the top rail in the at-rest position looks  a little odd. It's often a problem with "iconic" opening bridges that their sense of spectacle is lost when they are closed. With the Rolling Bridge, it still retains a sense of potential, like a muscle tensed and ready to flex.

Further information:

06 December 2011

London Bridges: 18. Helix Bridge, Paddington

The next few posts follow something of a guerilla tour around the footbridges of Paddington Basin, London. This canal terminus has undergone considerable redevelopment over the last decade, and a number of bridges have been installed both to improve access and to gain attention through their novelty value.

Before visiting, I'd heard of a fellow bridge photographer who had been unable to take pictures on the site thanks to over-zealous security guards. I'm a pontist, not a terrorist, but I thought it best to take photos quickly and not hang around. You'll therefore have to bear with me if some of the photos aren't of the best quality.

Somewhat prosaically also known as the "East Bridge", the tiny Helix Bridge provides access across the east end of the canal basin at Paddington. Completed in 2003, it spans a mere 7.2m. It was designed by Buro Happold with artist Marcus Taylor, and built by Davy Markham.

It is designed to retract, giving the impression of a corkscrew as it does so, albeit very, very slowly, moving at a snail-like 75mm per second. The "corkscrew" effect is simulated: the enclosure assembly rotates on bearings within the two circular end hoops. These in turn are supported from a retractable 2m wide walkway structure, which cantilevers from one end. This sits on a powered trolley, which runs on rails. As the walkway retracts, the enclosure rotates.

The 3.5m diameter enclosure comprises 15mm thick curved glass panels, glued to the tubular framing. The main spiral element is a 140mm diameter stainless steel tube. The bridge has clearly been altered since construction, with what were previously transparent panels now replaced or covered in blue material. I presume this is a response to vandal-related glass breakages.

I gather that the bridge has not been able to operate for some time, and have seen a comment from British Waterways on an online canal forum that it would "cost a considerable sum of money to repair", clearly disproportionate to the value that opening provides. BW also report that the bridge is due to be replaced by a new lifting bridge, presumably one with a less complex mechanism, and hopefully not destined for a similarly early graveyard.

Further information:

04 December 2011

London Bridges: 17. Challenge of Materials Footbridge

I spotted these photos from earlier this year lurking in my files, and realised it was a bridge I hadn't yet featured here. These aren't great photos, I was in a hurry and didn't have time to find a good viewpoint.

The bridge was designed by Whitbybird and Wilkinson Eyre and spans the main hall in London's Science Museum, providing access to the Challenge of Materials gallery.

The bridge is intended to use the bare minimum of materials, with 16m spanned by 8.5 tonnes of glass and steel. The deck comprises 828 glass plates placed on edge, the ideal arrangement to resist the compressive stresses introduced by the cable-stay support arrangement. The balustrades are in the form of glass plates.

The "stays" are a closely spaced fan of stainless steel wires, each a mere 1.58mm thick. Each wire runs from a support fan bolted to the building's columns, down to the deck, across the underside, and then back to another support fan. Tie-down cables below the deck ensure rigidity and prevent vibrations.

From several angles, as will be apparent from the photographs, the ultra-slender wires almost become invisible, leaving only an evanescent presence in the air. From other perspectives, the light glints off the wires, and elements of their cat's cradle geometry are revealed. This is my favourite aspect of the design: the supporting wires define a wider space for the walkway to rest within, but the effect is subtle rather than intrusive.

The glass floor and sides, which you might expect to give a sense of precariousness, are surprisingly unexciting: the sheer rigidity of the structure eliminates any sense of peril.

Further information:

02 December 2011

Bridges news roundup

It's time for another very quick roundup of bridge-related news.

Hopefully in the near future I'll get some more spare time, and I plan to post about a series of footbridges in the Paddington area of London which I visited recently.

Walk of Faith: Glass Pavement for Tourists Built on 4,690ft Mountain in China
That's another place added to my future holidays list.

Shrewsbury footbridge to undergo major refurbishment
£450,000 to refurbish a bridge which originally cost £2,600. It would certainly be a shame not to preserve this fine bridge, but you could probably build an entirely new bridge for that sum.

9 Beautiful Pedestrian Bridges Not Designed by Santiago Calatrava
The design credits generally omit the engineer, and several of these actually look rather horrible, but it's nice to see lesser known structures getting some recognition.

Peace Bridge placed over Bow River
The long-running saga of Calatrava's Calgary bridge seems to be approaching an end. Some people still find time to grumble.