Iceland Bridges: 4. Jökulsá á Dal Canyon Bridge

There are many arch bridges in Iceland, but this is probably one of the more unusual ones.

Built in 1994, this bridge is 125.5m long, with a main span of 70m. The steel-concrete composite road deck is supported on the arch via slender piers at 14m spacing.

The bridge was designed by Línuhönnun Consulting Engineers, who became part of EFLA Consulting Engineers in 2008. Swiss engineer Christian Menn was involved as a consultant.

The bridge is unusual for the arch being of composite construction, with a concrete slab supported on two steel box girders, and for its angular form. In the UK, we'd describe it as a "thrupenny-bit" profile. This solution was chosen over girder and framed options for aesthetic reasons, although studies showed a steel frame bridge to be slightly less expensive.

The composite form was chosen to eliminate the need for falsework as far as possible. The steel girders were erected first, and used to support 150mm thick prefabricated concrete panels. A further layer of in-situ concrete was then poured to create an arch 300mm thick in total. The width of the arch varies from 4.4m at the crown to 6.4m at its springings.

The bending stiffness of the arch and deck are similar, so in the finished bridge, they both resist asymmetrical bending equally.

The construction sequence had to be considered very carefully to ensure that the very slender arch remained stable at all stages - the construction photo below (taken from a technical paper describing the bridge's design and construction) shows quite how slender it appeared.

Further information:

• Google maps
• Structurae
• A Composite Arch Bridge, Iceland (Kristjánsson, Hjálmarsson, Einarsson and Haflidason, Structural Engineering International, 1996)

Iceland bridges: 3. Suspension bridge over Jökulsá á Fjöllum on Route 1

My journey took me east from the previous two bridges, following the Route 1 highway.

Iceland is well-supplied with large rivers, carrying meltwater from icecaps and glaciers. The Jökulsá á Fjöllum river appears wide but relatively unspectacular. However, the volume of water is substantial, as can be seen around 20 km to the north where the river spills over the enormous Dettifoss, reportedly Europe's largest waterfall.

Before there was a bridge here, the river could only be crossed by a ferry. The bridge was built in 1947, one of a number of suspension bridges completed within a 12 year period from 1945 to 1957, following Iceland's independence from Denmark.

The bridge is 171m long, with a main span 102m long and 3.7m wide. The steel ropes were supplied by British Ropes Ltd, and the steelwork was supplied and erected by Dorman Long.

The Icelandic roads authority have been planning a new bridge a little to the south of the existing structure, on the grounds that the existing bridge requires both speed and weight restrictions (lorries are forbidden by signs from travelling in convoy across the bridge). The new structure is proposed as a 5-span concrete box girder bridge, 230m long. Construction was due to start in 2015, but evidently it has been delayed.

Further information:

• Google maps
• Structurae
• Report on bridge replacement project
• Bridges of North and North-east Iceland

Iceland Bridges: 2. Road bridge over Skjálfandafljót at Fosshóll on Route 1

This bridge was built across the Skjálfandafljót river in 1972, replacing an older truss bridge dating from 1930. The older bridge (and the remains of its 19th-century predecessor) can be seen in the photo at the end of this post.

Today, this structure carries Route 1, the main Icelandic ring road. Like many bridges in the country, it is only a single lane wide, although reportedly the national highway authority is considering building a new 2-lane bridge immediately to the north of this span.

As with many bridges in Iceland, it can best be described as pragmatic. The ladder-like inclined legs allow the main bridge girders to be more economical in size.

Further information:

• Google maps
• Structurae
• Guide to Iceland

Iceland Bridges: 1. Former road bridge over Skjálfandafljót at Fosshóll

I visited Iceland earlier this year, and stopped briefly at a few bridges while there.

This first structure was previously a highway bridge spanning the River Skjálfandafljót. It carried Iceland's main ring road (Route 1) until a new bridge was built in 1972. The older bridge has been retained today as a pedestrian bridge.

The steel truss bridge was built in 1930, and replaced a previous wooden bridge dating from 1882-83. You can see the remains of the older bridge in the photos.

The bridge was refurbished between 1999 and 2000.

This must be one of the most-seen footbridges in Iceland, not because it is of any great interest itself, but because it is just downstream of the spectacular waterfall, Goðafoss. It provides a pedestrian link between car parking areas on each side of the river.

Further information:

• Google maps
• Structurae
• Guide to Iceland
• Bridges of North and North-east Iceland

Merseyside Bridges: 13. Bradley Swing Bridge

I crossed this bridge en route to its much bigger and better known neighbour, the Sankey Viaduct. It is a rod-stayed pedestrian bridge spanning the Sankey Canal, and although there may have been several bridges like this in the canal's heyday, I believe this is the only one of this type that is left.

The Canal dates all the way back to 1757, but Historic England suggest that the Grade II Listed bridge dates from around 1857. The Listing states that the turning gear and pivot remain in place, although clearly the bridge is no longer operational, and the canal reaches a dead-end a short distance to the north of here.

If the 1857 date is correct, it must be one of the oldest surviving stayed bridges in England (there are certainly older examples in Scotland). It's not clear how much of the bridge is original - Historic England date the parapets to the 20th century, and there are turnbuckles in the main rods which are clearly an alteration.

The bridge is currently painted black and white but was previously painted green, as can be seen in photos at the Towpath Talk website, and on Wikimedia Commons, so the repainting is fairly recent.

The bridge's most unusual feature is the way in which the main span stays split into two. The stays are flattened locally to allow a pin to pass through. Combined with the bending of the rod over the narrow width of the cast iron posts, this is not an arrangement which could carry substantial loads, it would too easily be prone to fracture.

At deck level, there is a short linking piece connecting the main stay to the floor beams, which don't look original to me.

Further information:

• Google maps
• British Listed Buildings
• Canal Plan

Merseyside Bridges: 12. Sankey Viaduct

Time for a couple more "Merseyside" bridges (using the regional term in a broad sense, before the pedants write in, again).

Completed in 1830, Sankey Viaduct has been described as "the earliest major railway viaduct in the world". Protected by Grade I Listed Building status since 1966, it still carries trains today.

The nine-arch viaduct was built as part of George Stephenson's Liverpool and Manchester Railway, to carry the line over a valley containing both the Sankey Brook and the Sankey Canal. The latter is now defunct, and was infilled at this location in 2002, so the viaduct now spans the Brook and a public footpath.

The viaduct is reported to have been designed by Stephenson's assistant Thomas Longridge Gooch, with William Allcard acting as resident engineer. Both men had worked with Stephenson for several years, and although Gooch is often described as Stephenson's draughtsman, he would in modern terms be called an engineer. Some sources cite Allcard as the main designer.

In 1825, Stephenson had been temporarily displaced as the railway's engineer, and John and George Rennie proposed a seven-arch viaduct 273 yards long. Once reappointed, Stephenson initially put forward a 20-arch brick viaduct, which was rejected by the railway company's directors. Describing his first design, Stephenson wrote to his son, Robert:

I have drawen a plan on the gothick principal there will be 20 arches of 40 feet span it will be quite a novel[ty] in England as there will be a flat arch sprung between the centre of the tops of the gothick and so on it has a fine appearance in the plans.

The Viaduct was only necessary at all because the Sankey Brook Navigation Company refused any obstruction to tall sailboats passing along their canal. Compare this old image of the viaduct with how the valley looks today.

The viaduct is a brick structure with sandstone facing on the two elevations. The piers are generously tapered and robust in appearance. Below ground, they sit on sandstone foundation blocks, which are in turn supported on driven timber piles.

The arches are semi-circular, each spanning 15.2m (50 ft). The keystone is prominent, projecting not just below the elevation, but below the entire width of the arch barrel. The underside of the arch is substantially covered in calcite staining, and in need of at least a clean if not more thorough refurbishment.

New overhead electrification portals were added in 2015; this seems to have been done with some sensitivity, choosing the positions carefully and only with small visible protrusions above the cornice line.

Looking up at the spandrel walls, occasional openings can be seen on one or other side of the central pilaster. I wondered whether these indicated the bridge to be of hollow-spandrel construction, with a series of internal spandrel walls. I found the planning consent application for the overhead electrification online, showing this guess to be correct, see the drawing extract below.

Further reading:

• Google maps
• Wikipedia
• Structurae
• Engineering Timelines
• British Listed Buildings
• Transport Trust
• Sankey Canal and Restoration Society
• British Railway Bridges and Viaducts (Smith, 1994)
• Civil Engineering Heritage: Northern England (Rennison, 1996)
• An Encyclopaedia of Britain's Bridges (McFetrich, 2010)
• Aqueducts and Viaducts of Britain (Owens, 2019)

Demolition of the Pont des Trous, Belgium

This wasn't a story I was aware of until I saw something recently posted on the Bridgehunter's Chronicles blog.

The Pont des Trous (translation: "bridge of holes") in Tournai was a medieval structure spanning the Scheldt River. Three arches, built at the end of the thirteenth century, connected two defensive towers, part of a historic city wall system. According to one report, this was one of only three remaining 13th century defensive bridges in the world (although ... read on!)

Here is this attractive heritage bridge pictured last year:

Image courtesy of Trougnouf via Wikimedia Commons CC BY-SA 4.0 license

And here is how it looked on 14th August this year, following major demolition work:

Image courtesy of Jpcuvelier via Wikimedia Commons CC BY-SA 4.0 license

If you spot that the towers look different in the two photos, that's because the photos are taken from different sides of the bridge: the curved tower faces were apparently on the outside of the city walls, to better deflect cannon-shot.

After much debate, the arches have been demolished in the name of progress. Apparently, the 1500-tonne vessels that could pass through the central arch are not enough, so the bridge had to make way to allow 2000-tonne vessels to pass.

Demolition of such a historic structure seems quite suprising, even with the stated justification of improving the local economy. There have been a petition against the proposal, and a Facebook protest group.

However, the structure that has been destroyed was not actually the original 14th century bridge, shown here in an old illustration with three equal gothic arches and a roof covering.

Image undated via Wikimedia Commons, public domain

The roof was removed and some other alterations were made in the 19th century.

The bridge was then destroyed by the British during the second world war. This image showing the damage to the medieval bridge dates from circa 1940:

Source unknown via delirurbain.org

When the bridge was rebuilt, it was essentially entirely erased and then reconstructed to some extent in reinforced concrete with a masonry facing - the bridge that has now been destroyed was essentially a fake, although many visitors would never realise this. The central arch was raised and widened enlarged at this time.

There have been various plans put forward to replace the demolished bridge with a modern structure.

Here is a proposal from Bureau Greisch and ANMA architects, a stainless steel mesh, a ghost of the bridge's former self in far too many senses:

A stone version of the same idea was preferred in a consultation with residents (although the consultation didn't include the possibility of retaining the existing structure).

This alternative proposal is from architect Olivier Bastin, a more skeletal reconstruction. It feels more like a parody of a bridge, than any meaningful tribute to what was there before.

Michel Wiseur's alternative is the best of this sorry bunch, displaying clearly the site's history rather than replacing it with something of entirely different dimensions or materials:

I gather that all these proposals have now fallen by the wayside, and the local authorities have stated they intend to rebuild the bridge (on another site?), stone-by-stone. If you watch the video of its demolition, you may wonder quite how that will actually happen.

My first thought on hearing about this whole story was that it was really quite appalling. Heritage can either be preserved or lost, and it can only be lost once. Once lost no Disney-like confection can replace it. However, here is a bridge that can apparently be lost twice, and the bridge that has been destroyed is not what it may have seemed.

So is it really such a loss after all? It is perhaps more significant as an element of civic identity than as a piece of real heritage. As with much nostalgia, the sense of loss is for a representation of the past that was never real or authentic anyway.