17 May 2016

French Bridges: 9. Passerelle du Paillon, Nice

Here's a second bridge from the French city of Nice.

The Passerelle du Paillon is a modern addition to the city, completed in December 2010. It's only a short distance from the railway bridge in my previous post, and it carries pedestrians and cyclists across the wide bed of the river Paillon.

The bridge was designed by noted French architect Alain Spielmann. Coyne et Bellier were the structural engineers, and Eiffage and J. Richard Ducros the contractors.

The budget for the 75m long bridge was 3 million euros, but completion of the bridge was delayed by a year when tenders came in 50% higher than expected.

The main mast is supported on a foundation comprising 30m long 1.2m diameter reinforced concrete piles. Two additional stub columns are located on the foundation, presumably to stabilise the bridge deck against twisting.

The bridge is a symmetrical cable-stayed steel structure, with a 25m tall steel pylon supporting twin decks in an "X" configuration. The 3m wide decks appear to comprise steel box girders on the inner edge, with an outer edge supported from cantilever struts.

Planters have been awkwardly placed at the entrance to each arm of the deck, presumably because the designer didn't consider that a 3m wide space might be attractive to drivers of small cars.

The outer edge of each deck is hidden behind a narrow steel fascia strip, presumably added to provide a clean line and hide the tip of the cantilever supports.

The layout of the bridge is much more attractive than a straight-line bridge would be, but strikes me as over-generous for the bridge's location and likely useage. It's well out of the city centre and alternative walking routes are available at a reasonably close distance, so the layout and dimensions appear excessive. I wonder what had to be omitted from the design to bring tenders back within the original budget?

The twin-span solution, with a single pier in the centre of the riverbed, is appropriate to the location. On the west bank of the river, the footway is narrow, but on the east bank it is wide. An asymmetrical design with an offset pylon could therefore have been feasible, with backstays landing on the east bank.

However, the chosen design minimises intrusive construction works to both banks, and the height of the pylon is perhaps more appropriate to the surroundings than would have been the case for an asymmetric solution.

For the most part, the bridge is well-detailed, without undue fuss. I like it.

Further information:

14 May 2016

French Bridges: 8. Railway Bridge, Nice

I'm going to feature a couple of bridges that I found last time I was in Nice, France.

I've done my best to find any information on this three-span masonry arch bridge, which carries a twin-track railway line in Nice across the Paillon, a seasonal river which is exposed here, but buried in a tunnel in most of the city centre.

I don't know when it was built, or by who, so please feel free to add information in the comments, if you can.

What I like most about this bridge is its clear, clean lines. Seen from far enough way, it could be mistaken for a concrete bridge, due to its sharp, hard lines and general lack of texture.

Seen closer to hand, the scale of the facing arch voussoir blocks is impressive. From below, it can be seen that the bridge isn't really made from such large blocks, but from more conventional coursed masonry.

The paleness and the hard edges to the masonry indicate that this is a well-engineered bridge, a work of rigour and certainty.

The bridge deck has been widened in concrete at some stage, but the lightweight balustrades ensure this has little visual impact.

The concrete "boats" which have been placed around the original stone piers are one of the bridge's least attractive features. The original stonework is left marooned, like a giant stepping across a river with her feet in saucepans.

Additional piers have been inserted halfway along the river spans, which help support a lower-level roadway bridge adjacent to the railway structure. Oddly, I don't think these are such a bad feature - they seem sufficiently divorced from the bridge above that it shrugs off their intrusion.

The addition of overhead electrification is less successful, with one support point above a pier, another above an end pilaster, and one in an awkward position part way long a span. It's hard to believe it would have cost much more to position every support symmetrically above the piers.

The bridge is generally in very good condition, except for a few areas of staining and this area of damage to a lower edge.

11 May 2016

Historic bridges widened to add footways or cycleways

One of my readers has written to ask whether I know of any examples of UK historic bridges (ideally Listed ones) which have been widened in modern times to increase capacity for pedestrians and cyclists.

From my previous posts, my personal favourite is Roxburgh Viaduct, with a footbridge added at a low level (although this is, of course, not a modern addition). A poor example is Byker Bridge, while I've covered Hungerford Bridge / Golden Jubilee Bridge on two occasions.

I can think of a few more, but I'd be interested to see what examples any other readers can suggest, both good or bad. Please post in the comments!

03 May 2016

Yorkshire Bridges: 11. University of York footbridges

I'll finish this short series of posts on the bridges of the University of York with a sampling of some of the other footbridges to be found at the University's Heslington Campus.

But first, I found a couple more photographs of the weathering steel footbridge, which make for an interesting comparison with my own photographs. Both of these are courtesy of the University's image library. They show the bridge as it was originally designed and built, not as hidden behind trees as it now is, and with a much more open and attractive parapet. It was clearly a genuine work of art, and deserving of wider recognition. Although it's still an attractive bridge, it's clearly not what it used to be.

Here are a few more of my own photographs of bridges at the University:


30 April 2016

Yorkshire Bridges: 10. Arched footbridge at University of York

Here's a third footbridge at the University of York. This one connects two college buildings across a small highway, and was built some time before 2010, although I can't find any information on the exact date, the contractor, or the designer.

This is a fairly straightforward steel arch bridge, although there are a few features of note.

The first is its asymmetry, with the arch ribs founded at one end close to deck level, and at the other end below deck level. I'm only guessing, but I wonder if this is due to an obstacle to foundations at one end, such as buried services. This may also explain the slightly odd struts supporting the deck at one end.

Joints in the deck edge stringers have been simply detailed, and most of the rest of the bridge is also straightforward and attractive, including the balustrades.

The choice of paving is unfortunate, with some of the paving slabs coming loose. I would think these will be a perennial source of problems.

26 April 2016

Yorkshire Bridges: 9. Cable-stayed footbridge at University of York

Here's another interesting little bridge at the University of York's Heslington Campus.

I've been unable to find out anything about when this bridge was built, or who was responsible, so if any readers can provide further information, please share it in the comments.

The bridge spans an artificial lake between two colleges, and fits the surroundings well, with a height that isn't any taller than nearby trees.

There are a number of things that I like in this bridge. The first is the very slight angle to the towers, which helps give it an open feeling, perhaps even a little jaunty. Vertical towers would look stiff and formal by comparison.

The towers themselves are nicely tapered, and attractively simple in their chevron cross-section, which ensures all sides of the steelwork are accessible for maintenance and repainting (or cleaning, should somebody be bothered).

I also like the way the towers are perched on tiny pin-pricks of steelwork, the entire bridge perched on as little as is necessary to hold it up.

I admire the modesty of the bridge deck, with simple timber decking and straightforward balustrades. The bumblebee ends to the balustrade rails, presumably intended to warn drunken students against tumbling against them headfirst, are the only jarring note.

24 April 2016

Yorkshire Bridges: 8. Weathering steel footbridge at University of York

I visited the University of York a while back. The main campus is built around an artificial lake which is crossed by a number of footbridges.

The weathering steel footbridge is not just any footbridge in weathering steel: it is claimed to be the first weathering steel bridge ever built in the UK, dating from 1967. With nearly half a century of weathering having taken place since construction, I thought this would be an interesting bridge to visit to see how the weathering steel patina can develop in the long-term.

As it turns out, the patina is probably the bridge's least interesting attribute. It's an attractive dark brown, which looks like it has stabilised well. There's no sign of ongoing corrosion anywhere, indicating that the bridge was well detailed, and no evidence of graffiti or other vandalism. The bridge drains freely into the lake via a series of scuppers along each edge.

The bridge's main interest is in its shape. It is wonderfully slender in elevation, broadly taking a three-pinned "arch" form which is vaguely reminiscent of Robert Maillart's Tavanasa Footbridge.

The deck consists of two steel box girders, each triangular in elevation. They are deepest at their points of support, which consist of slender steel box struts carrying the loads back to the abutments at a very shallow angle.

All this looks quite delightful in elevation, but is just plain odd when viewed at closer hand. The struts are much narrower than the deck girders, so it's apparent that there must be significant internal diaphragms within the boxes to transfer loads between the main structural elements. I'm struggling to see the rationale, either architectural or structural, for doing this, as the forces just don't seem to "flow" down to the ground.

Nonetheless, this is an attractive bridge, which has survived well, and clearly demonstrates both the longevity of weathering steel, and its ability to sit attractively within semi-rural surroundings.

There are some other interesting footbridges at the same site, I'll post details when I get a chance.