26 October 2019

"Tower Bridge: 1894 to date. Operations Manual"

Haynes Publishing must be best known for their car and motorcycle maintenance manuals, but they have increasingly branched out into other territories, with recent publications including "The Human DNA Manual" and the "Milky Way Owner's Workshop Manual". In the areas of architecture and infrastructure they have published Manuals for "London Underground", "The Great Pyramid", "Hadrian's Wall" and now "Tower Bridge" (188pp, 2019, ISBN 978-1-78521-649-7).

It is, of course, Tower Bridge's 125th anniversary this year, and this new book by engineer John Smith joins books by Kenneth Powell and Harry Cory Wright published to mark the occasion. A comparison against the Powell book is inevitable, and although there is plenty of overlap between the two, there are some very clear differences.

Powell's book has, on the whole, the better photographs, and is a much easier read for a non-engineer, with much more detail on the context and a strong narrative surrounding those who designed and built the structure. As befits its publication by Haynes, Smith's book has far more detail on the construction work, the bridge components, and its operating technology.

The early sections of the book give a fairly comprehensive account of the somewhat tortuous process by which the bridge was eventually conceived, including the sometimes ingenious and sometimes monstrous alternative designs put forward.

The real dive into detail begins in the third chapter, documenting the eight separate contracts which were let for construction of the bridge, dividing up the works required for the piers and abutments, approach structures, metal superstructure, masonry superstructure, hydraulic machinery, paving and lighting. No client today would take this approach, retaining the entire liability for integrating a complex construction process on their own, but when the bridge was built there would have been no single contractor with the capability to do it all.

It's interesting here to see the extent to which the contract conditions used in the 1890s are very similar to those still in widespread use at the end of the 20th century. Extracts from the very first contract (for the piers and abutments) make this clear: the power of the resident engineer, payment retention, liquidated damages etc. The unrealistic timescales demanded by the client, and unrealistic prices submitted to win the work, also remain familiar today.

The core of the book consists of four chapters which itemise every single element of the bridge, describing them in exquisite detail and explaining just how every piece fits together. At times, the level of detail presented, with dimensions, plate thicknesses, etc, is numbing rather than interesting. For the engineering reader, there are several interesting extracts from drawings included, and the comprehensive nature of the text does mean that there appear to be no significant details left unmentioned.

There are many aspects of the bridge explained here which are essentially absent from the account in Powell's book. One example is the presence of stiffening girders concealed within the balustrades of the southern span, which ensure that water pipes carried across this span were protected against excessive movement. Another is the explanation of the arrangement of the high-level footways, the suspension bridge ties which pass through these, and the additional suspension cable added in 1960 to relieve the footway girders of the weight of those ties. These elements of the bridge are not immediately apparent to the casual visitor, but Smith's text, photographs and drawings make everything clear.

The book contains one excellent cutaway diagram showing how the components of the bridge fit together, and it's a shame there weren't more. My over-riding impression, after reading this book, is quite how complex Tower Bridge really is, and how well it merits this wealth of information. It really is an engineering masterpiece, whatever anyone may think of its architectural merits.

The book concludes with biographies of the main participants in the bridge's design and construction, and a detailed timeline of alterations and maintenance work in the period from 1894 to date. One of three appendices gives a detailed breakdown of the author's calculations of loads and forces in the bridge's key structural elements.

I couldn't, with any honesty, recommend this book to anyone who is not an engineer, but it is so detailed that it will probably remain a key reference work for Tower Bridge for the indefinite future. It is clear, thorough (sometimes too much so!) and well-illustrated throughout.

13 October 2019

Lancashire Bridges: 8. Seven-arch Bridge, Rivington

This is an interesting bridge that I stumbled across on a visit to Rivington Terraced Gardens, near Bolton in Lancashire.

The Gardens were built over a two decade-period starting in 1905, for industrialist William Hesketh Lever, also known as Viscount Leverhulme. Lever made his fortune with his family firm Lever Bros (later to become Unilever), selling Sunlight Soap. He had made a home, the Bungalow, at Rivington, and the surrounding estate was landscaped by Thomas Mawson, who later became the first President of the Institute of Landscape Architects.

Most of the Gardens then fell into ruin, but a Heritage Trust has been busy in recent years clearing vegetation and conserving the site's historic structures (there are eleven Grade II Listed Buildings within the site).

The Seven Arched Bridge carries a footpath over an access track, and was reportedly inspired by a bridge that Lever had seen while visiting Africa.

Historic England lists the bridge as part of a group of structures including a staircase, walls and a summer house, all of which proceed up the hill from the bridge. All these structures are built in a common style using thin slabs of gritstone.

Historic England's listing suggests that the design for the bridge was based on a bridge in Nigeria. Lever did source palm oil for his soap from the British colonies of West Africa, but he is also known to have visited Belgian Congo (now the Democratic Republic of Congo) in 1911 to set up palm oil plantations.

There is an image of a bridge in Albertville (now Kalemie, in the D.R.C.) from circa 1930 which might be relevant - I've certainly not found anything else online (there are further images of the same bridge on these pages).

In any event, this is not an elegant bridge, but it is interesting for its unusual architectural style, and the way its robust mass is built up from fine detail.

Further information:

06 October 2019

"An Encyclopaedia of British Bridges" by David McFetrich

David McFetrich's "An Encyclopaedia of British Bridges" (Pen and Sword Books, ISBN 978-1-52675-295-6, 2019, 444pp) is the 2nd edition (with a very slight change in title) of a volume previously published in 2010.

It updates and expands its predecessor with one-third more structures discussed across 1,600 individual entries (previously 1,350), and a page-count increased by a quarter. Size does matter in an effort like this - it can never possibly be comprehensive, but an already impressive reference work has been made significantly more valuable.

The additions are from all periods of history, bridges both ancient and modern, and many of them are structures I'd never heard of. Picking the letter K at random, the bridges added are Karlsruhe Friendship Bridge, various Kew Gardens bridges, Kildrummy Castle Bridge, Glasgow's Kingston Bridge, and Knostrop Weir Footbridge. One of these is an inexplicable omission from the previous volume, and the others are all worthy inclusions.

The core of the book remains a well-illustrated alphabetised compendium of notable bridges (I should declare an interest here, as some images in the new volume have been provided by the Happy Pontist). Descriptions vary in detail but always convey the core facts and usually offer interesting information or context. Some entries have been expanded from the previous edition. The Encyclopaedia is frequently my first point of reference when investigating British bridges, and helpfully includes cross-references to other sources and a thorough bibliography.

The book is topped-and-tailed with a brief history of Britain's transport infrastructure, details of how bridges work, a fine glossary, lists of record-breaking bridges and a very helpful geographic index. A length "miscellany" puts the bridges in many different contexts, covering not just "timber bridges" or "suspension bridges" but less obvious subjects such as "tea house bridges", "relocated bridges", "finback bridges" and "ugly bridges".

Every time I open the book, I discover something new, and I imagine most readers will find the same. If you already own the first edition, it may be difficult to justify this new one, unless your interest in the subject is serious. If you don't, and you are at all interested in British bridges, I think this book is indispensable. If you are involved in the bridge design or engineering community, you may even find some of your own bridges here - I certainly did!

An Encyclopaedia of British Bridges is currently available at a discounted price of £54 (postage free in the UK) from the publisher, and also on Kindle via Amazon.

03 October 2019

Iceland bridges: 6. Hvítá bridge

This is the last bridge I'm going to feature from my Iceland trip, and it's the best.

When celebrating its 90th anniversary in 2002, the Association of Chartered Engineers in Iceland designated this bridge the most notable achievement of the third decade of the 20th century, the only bridge to make their list.

The bridge was built in 1928 by the national highway authority to a design by their engineer Árni Pálsson - it was one of the first projects in his career there, he went on to become their chief engineer in 1947.

The structure is 106m long, with two 51m span concrete arches spanning the river Hvítá (the "white river"). This structural form was chosen on cost grounds in preference to a two-span steel girder bridge or a one-span suspension bridge.

The structure carries the road Hvítárvallavegur between Hvítárvalla and Ferjukots. As you can see from the photo, this is a fairly rough highway, as with many in the country.

Prior to construction of the bridge, a ferry crossed the river, but this was unreliable when the river flow was high. Efforts to build a bridge began with surveys in 1910, and drawings were prepared in 1922, six years before construction eventually started.

The bridge would remain the main route from south-to-north in western Iceland until a bridge was completed downstream at Bogarnes in 1981.

The structure is instantly impressive, as attractive as many better-known concrete arches built in mainland Europe in this period. The 3m wide bridge was designed to carry a 6-tonne truck, or a uniform load of 400 kg per square metre (roughly 4 kPa), a similar load to what a pedestrian bridge would be designed for today.

The arch is very slender at its thinnest points, but unlike the broadly contemporaneous deck-stiffened arches of Robert Maillart (starting with the Flienglibach Bridge in 1923), it does not take its stiffness from the road deck.

The bridge draws its strength from the shaping of the arch - its connection to the deck at the middle of each span, and the thickening of the arch towards each support. This could have led to an ungainly appearance, but the sinuous profile of the upper arch surface combines well with the elliptical profile of the underside.

The set-back of the vertical support struts from the edges of the arch and deck also contribute to a fine appearance, emphasising the profile of the arch.

There are many more interesting bridges in Iceland, I only had time to visit a handful. Hopefully I'll get the chance to see more on a future trip!

Further information:

01 October 2019

Iceland bridges: 5. Jökulsárlón Bridge

This must be another one of the most-seen bridges in Iceland. It spans the outfall river from the Jökulsárlón glacier lagoon, and carries the island's ring road, route R1. You can't drive along the south coast of Iceland without eventually passing over this bridge.

The hengibrú (suspension bridge) was built in 1966-7, and has a main span of 108m. A ferry operated here from 1932, but before that the river was very difficult to cross.

I believe this was one of the last of a series of suspension bridges built in Iceland starting in 1945, and there are obvious similarities to the bridge over Jökulsá á Fjöllum that I featured previously, even though that is 20 years older.

When the bridge was built, the glacier Breiðamerkurjökull extended much closer to the highway. The glacier lagoon has grown steadily as the glacier has retreated, some 5.6km in the last century. This location, hugely popular with tourists, will at some point likely become the mouth of a new fjord, with the extent depending on how successfully global warming is tackled. Although efforts have been made to protect the foundations of the bridge against scour, it's lifetime may be limited.

Further information:

29 September 2019

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:

26 September 2019

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:

24 September 2019

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:

21 September 2019

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:

27 August 2019

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:

25 August 2019

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:

21 August 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.