03 December 2014

Bristol Bridges: 4. Meads Reach Bridge


This bridge was another early morning visit, to an award-winning span which is probably unique in Britain.

Built in 2009 for £2.4m, the 55m long bridge is a rare all-stainless steel structure. It was designed by Price & Myers with Níall McLaughlin Architects, and built by M-Tec. You'll see it described on the internet as a "stressed skin" bridge, to make it sound like it's using aircraft technology, but to bridge engineers it's simply a twin half-through box girder bridge, conventional enough except for the geometry and material.

The two edge girders hold up the bridge and also double as parapets. They consist of continuously welded, perforated Duplex 2250 stainless steel plate (supplied by Outokumpu), wrapped around triangular diaphragms. A series of cross-beams and bracing frames are hidden within the deck, which is surfaces with perforated stainless steel planks (of which, more later). The entire bridge weighs about 75 tonnes, and sits on four hidden stub "legs", one at each corner.

The extensive use of stainless steel is a bold, and presumably expensive, choice. The bridge's skin is punctured with thousands of small holes, arranged in size according to the calculated level of stress at each point of the girder surface. The process of analysing the bridge, determining acceptable levels of perforation, and translating that back into a fabrication model, will have been complex and demanding, and is an impressive achievement.

Luminaires are located within the girders and below the bridge's floor, and the perforations allow the structure to glow from within at night.

The bridge won the IStructE Structural Award for pedestrian bridges in 2010, and I think justifiably so, as it is highly innovative and geometrically challenging. I haven't seen it illuminated at night, but in daylight, sunlight reflects off the skin in a very attractive manner. However, the bridge is not without its critics.

The main complaint appears to relate to the deck panels, which are clearly very slippery, to the extent that the bridge is disfigured by prominent warning signs at each end advising users to cross with care. Reportedly, bridge users who do slip and fall have frequently been injured by the "cheesegrater" quality of the decking. In one month, over 600 people signed a petition asking for the bridge decking to be replaced.

However, as with the nearby Valentine Bridge, this is a public amenity which is privately owned. Although the decking is clearly not fit for purpose, the public may find it hard to force change.










Further information:

25 November 2014

Bristol Bridges: 3. Valentine Bridge

I'm nearly caught up on a backlog of bridge visits. The next two are both in Bristol, where I've previously covered Clevedon Pier (yes, I know that stretches the definition of "Bristol" and "bridges") and Pero's Bridge.

Valentine Bridge was built in 2000 by Alfred McAlpine, to a design by Atkins. The steel cable-stayed bridge carries pedestrians and cyclists across Bristol's Floating Harbour close to Temple Meads railway station.

As with the nearby Meads Reach footbridge (for which, see the next post), the bridge was privately funded and is privately owned.

The structure is S-shaped in plan, with a triangular cross-section framed truss deck. The upper and lower chords are circular steel tubes, connected by I-section struts in a Vierendeel arrangement.

This is not a good bridge.

It seems evident that the client must have wanted a "landmark" bridge of some sort, hence the mast, cables, and general layout. However, little effort seems to have been put into creating an efficient or well balanced structure. Of the four back-stay cables, two are so slack as to appear un-stressed, presumably a result of a cable layout which appears baffling when viewed from overhead. A balanced layout could have been achieved with fewer cables working more effectively.

Some of the cable detailing also looks a little awkward, perhaps cheap, especially the anchor detail to the deck.

The curved stainless steel parapets seem to be trying a little too hard, with an over-pronounced arc to the parapet posts. The abutment at one end, a mix of bold brick and prison-fencing (to guard the bearings), is quite unfriendly, as are the (pointless) anti-cycling barriers which block the walkway entrance.

Most annoying of all is the decking, which seems to have been fixed incorrectly, making a pronounced clattering sound each time someone crosses the bridge. If you watch the video below carefully, you can see the deck planks actually bouncing up and down.












Further information:

21 November 2014

"Bridges in Slovakia" by Peter Paulík

Bridges in Slovakia (Jaga, 272pp, 2014, also available in Slovak) [amazon.co.uk] is a lavish coffee table gazetteer, a real labour of love, and a book I would unreservedly recommend to Pontists everywhere.

Peter Paulík is a Slovak engineer who spent roughly two years touring his country, photographing, researching and writing this book. The result is a very well-produced effort, well designed and with large, full-colour photographs and diagrams on almost every page. You can get a good idea of the content without buying the book, as Peter has made the whole book available entirely free of charge in PDF format.

Amazon are currently listing this book, but I think it's best to buy directly from Peter online, the cost is only €36 including postage (in Europe), which is astonishingly cheap for such an large and well-illustrated volume.

The book opens with a series of prefaces and introductions, of which Paulík's short account of his bridge-hunting expeditions is the most interesting - he has braved real difficulties to locate and photograph some of the structures. There's also a good introductory guide to types of bridges, with very clear diagrams, some statistics on the number and type of bridges in Slovakia, a timeline and list of particularly significant structures.

The main section of the book is the gazetteer, arranged alphabetically by location. This covers all types of structures, from all periods of construction. Each bridge has a photograph or historic illustration, map coordinates, and explanatory text. Some structures are accompanied by further photographs and extracts from technical drawings.

Many of the bridges are relatively ordinary, but there are many which are beautiful, unusual and interesting. Major structures are given more attention and space. The photographs are generally of a
very high quality.

For anyone with a particular interest in Slovakia's architecture or infrastructure, this is an essential book. For other bridge enthusiasts, it is still a very enjoyable and informative tome. I think most of the bridges are little known outside their own nation, but many deserve wider attention. There are some gorgeous masonry arch structures; oddities such as a wooden "ecoduct", a bridge made from an old railway carriage, and an airport runway lighting bridge; and hosts of intriguing bridges in modern materials. As well as the masonry spans, I particularly like a number of small suspension bridges and pipeline structures.

Hopefully the book will bring the rich heritage of bridge design and construction in Slovakia to much wider attention.

19 November 2014

Bridges news roundup

It's been a long time since I've done a bridges news roundup, so I'm going to keep most of these links short and sweet.

COBE, COWI and DISSING+WEITLING Wins Competition to Design 225 Metre Pedestrian Bridge for Køge
"Functioning as a solar screen on the south, pedestrian bridge opens to the city and provide panoramic views to the north."

Bouncy Squibb Park Bridge Closed For Being Too Bouncy
"It was designed to bounce (similarly to trail bridges in the woods) ... its movements had substantially increased, causing concern. It also started to tilt and sag in sections."

What a FAN-tastic design! Engineers create London footbridge that unfolds like a paper concertina
National newspaper in "gives credit to engineers" shock!

Footbridge Ribja brv / Arhitektura d.o.o
"Our aim was to design a bridge that has a construction as thin as possible, and bridge railing as transparent as possible."

Skyttelbron Bridge / Metro Arkitekter (Sweco Architects)
"The first idea, and perhaps the strongest in terms of design is that we wanted to bring color in an environment where virtually every­thing is in shades of gray, brown or green."

Bridge Over the Rhone / Meier + Associés Architectes
"This unity of form 'strides' over irregularities in the terrain and interacts logically with the location by progressively increasing its span in line with the mathematical principle of harmonic curves."

Floating bridge by RO&AD crosses the moat of a Dutch fortress
"The new 80-metre-long bridge follows the original route boats would have taken between a jetty on the edge of the moat and a raised entrance situated in one of the fortress's walls."

Must have a head for heights! London's Tower Bridge unveils £1m glass walkway 140ft above River Thames... costing just £9 to visit
"The pedestrians milling about on the pavements look as if they have come to life from a Lowry painting and there is nothing between them and my boots but a sheet of glass."

What Montreal’s All-New Champlain Bridge Should Look Like
"A peer of Taillibert, fellow architect Pierre Briset, is not confident in Taillibert's proposal. Briset believes Taillibert's plan is just a ripoff of the Millau Viaduct in southern France."

Calgarians celebrate bridge opening
"At a cost of $25 million, the span took five years to complete, one year longer than anticipated after the first bridge deck was destroyed in the 2013 flood."

Designer of Verrazano-Narrows Bridge: Low-profile genius preferred anonymity
"The greatest monuments to pioneering structural engineer Othmar H. Ammann are the ever-spectacular bridges born of his brilliance."

Léon Blum Viaduct Bridge / RFR
"We have chosen to create a structural continuity between the bridge deck and its vertical supports which are articulated at their base. In doing so, the area of the bridge which is most directly in contact with the town is freed from the kind of massive support commonly associated with this type of Bridge."

18 November 2014

Danube bridge competition winner announced

Marc Mimram has beaten seven other teams to design a new €60m highway and tram bridge over the Danube in Linz, Austria. The other competitors included heavyweights such as Leonhardt Andra, Flint and Neill, Knight Architects, Dietmar Feichtinger and Dissing + Weitling.

It's a big bridge, some 30m and 400m long in total, and it's perhaps surprising to see a winner which is an essentially entirely new type of bridge. Essentially, it's a steel cantilever bridge along the lines of the Forth Railway Bridge, but with a number of unusual features.

The cantilever trusses are curved rather than comprised of straight pieces, requiring significant quantities of additional steel to resist the local bending induced in the steelwork. Very limited support is provided to the deck, which therefore has to be excessively deep.

The oddest feature, however, is the fact that the cantilevers sit on single lines of bearings, so that under uneven loading, the only stability is provided by the connection between adjacent cantilevers. Those short connection pieces don't really look stiff enough to provide that stability, and I wonder quite how the engineer has persuaded the design to work.

Of the other designs, the 4th prize entry is the most ambitious, with what appears to be a 250m span network arch bridge (just shy of the existing longest span of this type), a very challenging and complex structure to build.

Winner - Marc Mimram





2nd Prize - Öhlinger+Partner ZT GesmbH, Ponting Consulting Engineers and Zeininger Architects

3rd Prize - Gruppe VCE Vienna Consulting Engineers ZT GmbH, FCP Fritsch, Chiari&Partner ZT GmbH and Quist Wintermans Architects

4th Prize -  SSF Ingenieure AG, ISP ZT GmbH and Knights Architects

17 November 2014

Heatherwick's Garden Bridge gains planning consent from Lambeth Council


Love it or loathe it, the world's most expensive pedestrian bridge has now secured half of the planning consent that it needs to go ahead. Of course, I loathe it. It's an utterly disgraceful waste of public money in a location which doesn't need another tourist attraction, nor need to be the site of a bridge which would permanently wreck the London riverscape.

As with the ill-fated River Wear Crossing in Sunderland, public opinion has been consistently misrepresented by its backers. Other than one or two people involved with the design team, I've not met a professional bridge designer who likes it. The architecture critics see it for the white elephant that it is. Even London's mayor doesn't quite see why he's spending public money on it. A highly critical and cogent campaign against it by local residents seems to have fallen on deaf ears.

What's clear about the Garden Bridge is how the cult of celebrity provides a comfort blanket allowing people to suspend their normal critical faculties. It's got Heatherwick, it must be good. Joanna Lumley likes it. It seems clear that, short of hoping for the bridge to fail to secure the necessary funding or to come in way over-budget once it reaches construction tender stage (both being quite realistic possibilities of course), the only way to put a stop to this fiasco is for the designers themselves to wake up to the realities of their iconic fantasy, do the decent thing, and quit.

15 November 2014

French Bridges: 7. Pont du Gard

This is the final bridge in this series of posts about the bridges of southern France.

What can I say about the mighty Pont du Gard, justly the most famous of the surviving Roman aqueducts, a magnificent bridge, a World Heritage Site, a gorgeous, golden-hued monument to the achievements of antiquity?

I'll try to avoid the obvious: there are plenty of websites and books, linked at the bottom of this post, which will tell you all you need to know about how big it is, when it was built, and why.

A few thoughts:

The site of the bridge is well looked after. An exhibition is tucked well away from the river gorge, and a cafe and restaurant are both a discrete distance away from the bridge. It's a great spot to picnic, and to swim in the river.

The arches on the lowest tier are each built in four parallel sections, and those of the middle tier in three parallel sections, all without any mortar (only the top tier was built with mortar). I noted the same feature at the Pont d'Avignon, and presumed it allowed the builders to reuse the timber centering multiple times. That first ring of massive stone blocks would have felt pretty precarious, though. Paillet's paper on the bridge (linked below) suggests instead that the centering was for the full width of the bridge, and the parallel sections were just adopted to simplify the size of blocks that the masons had to be cut, making all the voussoirs identical. I'm not entirely convinced by this argument.

There are a multitude of projecting stones on both the side faces of the bridge and the support piers, but also, more unusually, within the arch barrel itself. These were normally used on arch bridges to provide support to the temporary timber centering. I don't think I've ever encountered corbels in the arch barrel itself before. Is this a common feature on Roman bridges?

The lowest tier of the bridge was extended in the mid-18th century, creating a new highway bridge parallel to the Roman bridge and butting up against it. Some effort was made to make this similar to the older bridge, but the stonework is very different, as are the cutwaters. Most noticeably, the old bridge is level, but the new bridge is ramped up towards its centre point, seriously spoiling the appearance of the bridge from both sides. It's no surprise that most "postcard" views of the bridge are therefore taken from the unaltered elevation.

More positively, the extension bridge does allow people to appreciate the monument from close up, without exposing it to the deterioration that would inevitably result if large numbers of people were encouraged to clamber upon it.

















Further information: