15 January 2017

French Bridges: 15. Pont d'Arcole, Paris

This bridge is on the site of a long-since-demolished suspension bridge, the Passerelle d'Arcole, designed by the great French engineer Marc Seguin. The two-span footbridge was replaced from 1854-1856 by the present bridge, designed by Nicolas Cadiat and Alphonse Oudry, in order to establish a crossing for heavier vehicular traffic.

The bridge is a single arch span in wrought iron, 80m long. It sagged suddenly in 1888, leading to strengthening, apparently by adding "two additional trusses".

I wonder if this accounts for the peculiar elevations of the bridge. In my photos you can see that there are reasonably stiff arch ribs, connected to the deck by two superimposed truss systems. There is a larger "W" pattern truss, and then additional triangulation is present in the upper half of the panels only. I'm thinking that this additional metalwork was a later addition, which would have served a dual function, of bracing the main diagonals against buckling, and of introducing more frequent points of support to the main deck elements.

However, this may just be a peculiar feature of the original design. The Planete TP website offers this explanation of the strengthening, which I can't make great sense of:
"In 1889, intermediate arches were added under each footpath and the longitudinal girder anchors were removed from the abutments as they had been responsible for structural defects."
As can be seen from the photos, the bridge looks very good lit up at night (although one panel of balustrade lighting was out of action). It gives a very crisp profile to the ornate balustrades. You might think that a triangulated truss bridge would look less attractive than its neighbours, but I don't think this is the case.

Further information:

12 January 2017

French Bridges: 14. Pont Marie, Paris

I've skipped a couple of bridges, and now we've switched to the right bank channel of the Seine, heading back downstream past the Île Saint-Louis.

Pont Marie is Paris's second oldest surviving bridge, completed in 1635, some twenty-eight years after the oldest surviving bridge, Pont Neuf. It is named for Christophe Marie, who proposed it in 1608; Marie is variously described as a developer and as an engineer. When the bridge was proposed, the island was actually two islands, largely used for pasture, and the bridge was built to facilitate house building. Started in 1614, the same year the islands were joined into one, the bridge took two decades to build.

The structure has five arch spans. There is a niche above each pier's triangular cutwater, intended to house statues, but no statues were ever installed on the bridge. As with many bridges of the period, wooden houses were built on the bridge, eventually being removed in 1788. Again, as with many nearby bridges, the bridge has been repaired and altered on several occasions, including reconstruction of two arches between 1660 and 1670 following collapse caused by a flood, and major works in 1850-51.

As can be seen in my photographs, the largest span is not the central span, but the second span from the left, which is elliptical, while the others are semi-circular. I'm not sure whether this relates to the partial reconstruction of two arches.

Whitney comments on the bridge:
"The ornamentation of the bridge is refined and in good scale. The plain masonry and the proportions of piers and arches give the bridge an appearance of dignity and great strength".
I am happy to agree.

I find it interesting that such an asymmetrical bridge can be regarded so highly - nobody would design a bridge of this type in such a way now without expecting adverse comment. I suspect most observers simply never spot the odd-arch-out.

Further information:

10 January 2017

French Bridges: 13. Pont au Double, Paris

The Pont au Double was originally built in 1634 to connect the Hôtel-Dieu on the Île de la Cité (an early hospital) to an annexe on the left bank of the Seine. The bridge accommodated further hospital buildings along its length, but was also open to the public as a toll bridge, with the fee being a double denier, hence the bridge's name.

This twin-arch bridge was replaced by a single arch structure in 1848 to improve river navigation, and then again in 1883 by the present-day structure, designed by Jules Lax. Today the bridge provides a key link from the left bank of the Seine to the piazza in front of the Notre Dame cathedral.

Various sources describe the bridge as wrought-iron with steel bracing, but this seems self-evidently incorrect. Seen from below, the 11 arch ribs can be seen to be made up of short cast iron segments, although the bracing may well be different in origin.

The two edge arches, and the balustrade above, are coated in copper, a highly unusual feature which makes the bridge gleam in the sunlight. The bridge was extensively refurbished around 2002-2004, and photographs from before this show the copper in its distinctive green weathered colour.

The French edition of Wikipedia refers to a copper galvanising process developed by M. Oudry, which is described in a book on electroplating of metals. The process involves specially varnishing and treating the cast iron before placing it in a bath of copper sulphate, which coats the cast iron object through the normal electrical galvanising process.

I guess the use of this process may explain the short length of the cast iron segments on the bridge, which would have to be short enough to be placed into a galvanising bath.

It's not clear how the coating was re-applied in the 2004 restoration project: there was an article in Bulletin ouvrages métalliques but I don't have a copy, so if any reader can shed more light, please do so!

I'd also be interested in examples of any other bridges where the same treatment has been applied, if there are any. It seems quite unusual, but it's certainly responsible for a key part of the bridge's beauty.


Further information:

08 January 2017

French Bridges: 12. Petit Pont, Paris

I'm continuing with bridges heading upstream along the Seine.

The Petit Pont is at the site of some of the oldest bridges in Paris. Bridges here reportedly date from Roman times, with Emperors Caesar and Julian both writing about bridges spanning across the Seine to the Île de la Cité. A bridge on this site has been destroyed and replaced on numerous occasions.

The present bridge was designed by Alexandre Michal and built by Ernest Gariel from 1852-1853, replacing a previous three-span structure, in order to improve river navigation.

The resulting bridge can at best be described as sturdy, cut from a rough-hewn type of stone which can be seen on other structures in central Paris.

[PS: Readers interested in seeing these Paris bridges, and many others, photographed a few years ago and in daylight, should check out the Bridge of the Week blog - follow the links for April and May 2009.]

Further information:

06 January 2017

Footbridge Awards 2017

The triennial, global Footbridge Awards have returned in time for the Footbridge 2017 conference.

Pedestrian and cycle bridges opened to the public in the years 2014 to 2016 are eligible for submission in one of five categories:
  • Short span: For new footbridges with a maximum clear span of 30m or less
  • Medium span: For new footbridges with a maximum clear span of between 30m and 75m
  • Long span: For new footbridges with a maximum clear span greater than 75m
  • Renovation: For a project to renovate or refurbish an existing footbridge, or to repurpose another type of bridge to be used by pedestrians, cyclists and/or equestrians
  • The Jonathan Speirs Lighting Award: For a lighting scheme on a new or existing footbridge of any size. Created in memory of Jonathan Speirs of Speirs and Major. 
Award entries need to be submitted by 6th March 2017, and the winners will be announced at the Footbridge 2017 conference in Berlin on 6th September 2017.

05 January 2017

French Bridges: 11. Pont Saint-Michel, Paris

From the Pont Neuf, the next few bridges are heading upstream along the Seine between the Île de la Cité and the river's left bank.

The Pont Saint-Michel was built in 1857, on the site of several predecessors.

A bridge was first built here in 1378, complete with houses on both sides. This was destroyed by ice in 1408, and a timber bridge built in its place 8 years later. It took its name from the nearby Chapel of Saint-Michel.

The timber bridge was destroyed when hit by boats in 1547, and rebuilt quickly a second time in timber. At this time, the bridge still had houses along its length, shown in a contemporary painting. This bridge was destroyed by more ice floes in 1616, and replaced for the first time in stone 8 years later. The stone bridge had four arch spans, and initially supported houses until these were removed in 1808. It was founded on timber piles.

The present bridge was built to a design by Paul Vaudrey and Paul-Martin Gallocher de Lagalisserie. with only three arches, presumably to improve navigation and allow water to flow more freely. In honour of Napoleon III, it is adorned with the large capital letter "N" surrounded by laurel leaves, a feature also of the Pont au Change, designed by the same partners and completed in 1860.

The bridge is notorious as the site of the appalling 1961 massacre of Algerian protesters at the hands of the French police force.

I only saw this bridge from the river, so don't have many photos, but I thought it was worth featuring due to its interesting history.

Further information:

03 January 2017

Bridges to Prosperity Christmas Appeal

Christmas may have been and gone, but I thought it was worth a mention for Bridges to Prosperity's Christmas appeal, as there's still time to donate.

As hopefully most of my readers will know, the charity builds pedestrian bridges in some of the world's poorest and most remote rural communities, enabling people to reach schools, markets, health care and many other facilities.

Here are a few key statistics taken from B2P's UK Charitable Trust appeal email:

  • The World Bank estimates that there are more than 1 billion people globally (that's about 1 in 7) who lack year-round safe access to fundamental basic needs;
  • Bridges to Prosperity can construct a footbridge in just around three months;
  • Local government investment averages 50% for each project, meaning that B2P works closely to empower local communities with every bridge build;
  • Communities receiving a footbridge show a 12% increase in school attendance, a 24% increase in healthcare treatment, a 15% increase in local business, and an 18% increase in women in employment.

Here's what B2P UK Trustee Ian Firth has to say:
"The statistics are captivating, but what really motivates my work with B2P, more than any statistic, is the time I have spent in country with the communities served by our bridges.  Local residents, trained by our teams, have worked alongside us to construct their bridge, and are deeply invested in maintaining it. Mothers and fathers are no longer nervous to send their children to school or the market on their own, and farmers will plant a wider variety of crops because they don’t have to worry about being able to reach the market, no matter the season. Lives are saved because the health clinic or hospital is reachable year-round, and families are reunited across an otherwise-impassable river. It's this sort of transformative change that B2P is all about – safe access, for all.
"Last year, B2P built 37 footbridges serving 150,000 people in all. Next year, our goal is to build 42 footbridges, and to serve our 1 millionth person over B2P’s fifteen-year history. To do so, we have to raise £10,000, and we need your help."
If any of my readers would like to donate towards the appeal, you can do so online.

More information about the charity and its work can be found at their appeal website (it includes links to several other fundraisers which may be relevant to readers wishing to donate in US$ rather than £UK).