Telford Station footbridge

Recently, I was in the town of Telford in Shropshire, and spotted this fairly spectacular new covered footbridge. It connects Telford Central railway station to the town centre, and replaces a previous bridge which was in poor condition. The new bridge opened to the public on 30th November 2018, with the project costing £10.3 million.

There are actually two new bridges, each with a similar design by Jacobs and Nicoll Russell Studios. They were fabricated by SH Structures working for main contractor Balfour Beatty.

The shorter structure spans over two railway tracks, while the longer structure is an impressive 90m long and crosses a dual carriageway road. It's not easy to photograph in a way that makes sense of both structures and their relationship to their surroundings, but you can get all that in this fly-through video:

The main bridge structure is a hybrid steel arch truss. The exploded view below, taken from a design drawing, shows the various structural and non-structural elements:

The form of the bridge is responsible for many of its oddities. The primary structure is an arched truss, entirely hidden within the roof, supported on raking legs at either end.

The central ridge to the roof initially gives the impression that the whole thing consists of two arches inclined against each other, but this is not the case: the raking legs are parallel rather than inclined inwards. It feels like a strange kind of compromise, perhaps benefiting from being largely hidden.

The outer roof covering is tensile PTFE fabric, tensioned against the steel members at each roof edge. The roof soffit is made up of GRP panels fixed to a grid of secondary steelwork, and hidden edge gutters are also constructed in GRP (there are plans and sections on the project website, for those interested in seeing more).

The hanger members are solid structural steel elements, suspending a stiffened steel grid deck (note that the drawings on the website show something different, a steel deck pan filled with concrete).

There are "swallow-tail" details extending the roof covering at each end of each span, which I think would have been better if more flamboyant, or at least if extended to fully cover the space between the two bridges (as things stand, bridge users will have a peculiar experience on a very rainy day).

A consequence of hiding the main truss inside the roof is that the hangers disappear into a featureless ceiling, which feels oddly disconcerting to me.

It's not obvious from the photos, but the roof structure is 7m wide, and hence much larger than the bridge deck, which has a clear width of only 3m (at least according to the design drawings on the project website). There's a certain top-heaviness which results, which is emphasised further by the extreme transparency of the deck and glazed walls. It's a bit like a glass of beer with too much foam left on top.

I do like the commitment to transparency, as covered bridges often give a very enclosed feeling. It lightens the overall impression of the bridge, giving good views for bridge users and I'd think a greater feeling of security as a result.

The bridges include two unusual curved expansion joints, and the larger span incorporates holding down bearings, presumably to resist overturning under high wind loads. Tuned mass dampers have also been installed, reportedly the first use of magnetic / eddy current dampers in the UK.

Further information:

• Google maps
• Project website (including live webcam)
• Bridge installation simulation video

London Bridges series: 53. Holborn Viaduct

I suspect that for many people, Holborn Viaduct in London is known mainly as a street name rather than as a bridge: the street extends for around 425 metres (1400 feet) between Holborn and Newgate Street, but only a relatively short length of bridge is visible where the street passes above Farringdon Street. Elsewhere, most the street is hemmed in by buildings either side.

What can be seen today bears little resemblance to how this site looked in the past. What is now Farringdon Street was once the River Fleet, running north to south through a valley before spilling into the River Thames. The Fleet can be seen on the mid-16th century "copperplate map" of London, which also shows the old Holborn Bridge which then spanned the river.

Fleet Ditch was used as an open sewer, and was eventually covered over, section by section, and converted into a buried sewer. Today it remains there, running below the roadway down to the Thames.

Between 1863 and 1869, the entire valley was improved in a scheme designed by city surveyor William Haywood. The southern end of the scheme included the reconstruction of Blackfriars Bridge, while at Holborn, the old bridge was removed and replaced with what is now Holborn Viaduct. Haywood worked with engineer Rowland Mason Ordish on the viaduct's design.

Source: Grace's Guide

A contemporary drawing (above) shows the full extent of the Holborn Viaduct construction. Most of its length consists of brick arch spans, enclosed on their ends to form chambers, and in addition to the Farringdon Street structure, there are special spans over other roadways and railways. A drawing made in 1941 reveals the structure, exposed by bomb damage to adjacent buildings (below).

Source: drawing by Louisa Puller, via Wikipedia

Work on the new bridge started in 1867 and was completed in two years. The spans over Farringdon Street use paired cast-iron arched members supported on granite piers. The decking was originally constructed from cast-iron troughing topped in mass concrete.

On all four corners of the bridge, a large building was constructed to house a staircase connecting the upper and lower roadways. The one shown in my photograph is a post-war reconstruction, as the two north buildings were damaged by bombs during the Second World War.

The visible bridge is spectacular and ornate, and does make me wonder quite how its construction was funded. It is adorned with ornamental lighting, four statues (representing commerce, agriculture, science and fine art), and the ironwork on the main elevations is finely detailed and highly decorative.

From below, entrances into the masonry vaults can be seen, and perhaps income from letting these spaces and the staircase buildings helped contribute towards the cost of construction.

It can also be seen that the bridge has been extensively altered. By the end of the 1980s, the deck was found to be in poor condition due to water penetration, and calculations suggested the bridge to be seriously under-strength for modern heavy goods vehicle loads. DHV Burrow-Crocker Consulting (since merged into the Waterman group) were appointed to examine, assess and design improvements to the bridge.

The altered arrangement is visible in the photographs and explained in a diagram below taken from a 1993 technical paper. The existing decking was completely removed, and new steel-concrete composite decks inserted in between the cast-iron arch girders. The existing piers were extended upwards in reinforced concrete to encase the ends of the cast iron members, and the new bridge deck was supported via bearings onto the concrete extensions.

It's an exemplary piece of engineering, leaving the historic structure seeming largely unaltered from most point of views, and retaining most of the original fabric. The extensions to the piers are especially well-detailed, and I would not have noted them if I hadn't read the paper.

Further information:

• Google maps
• Wikipedia
• Structurae
• Grace's Guide
• Patrick Baty (history and paint analysis)
• Inspection, assessment and strengthening of the Farringdon Street bridge, Holborn Viaduct (Carruthers and Shiel, in Bridge Management 2, 1993)
• Civil Engineering Heritage: London and the Thames Valley (Smith, 2001)
• An Encyclopaedia of Britain's Bridges (McFetrich, 2010)

Bridge competition debris part 29: Network Rail Footbridge Design Ideas Competition

I posted last July when Network Rail announced this contest, but what with one thing and another, I've neglected to write about the result.

Quick recap: Network Rail were looking for ideas which were "innovative, challenge presumptions and raise expectations for the quality of future designs". The contest ran alongside a more conventional commission for a consultant team to refresh the organisation's station footbridge designs, which led to the appointment in October of Arup and Knight Architects.

The ideas competition was open to pretty much any entrant, offering a £20,000 prize fund but no commitment to use the winning idea or to commission any further work.

The winner was announced in December as Gottlieb Paludan Architects, Denmark, with Strasky, Husty and Partners Ltd, Czech Republic (above). The judges also highly commended a design from Hawkins\Brown with WSP (below).

There were a further 18 entries on the judges' longlist. In total, 121 entries were submitted, so clearly something about this contest struck a chord amongst the creative professions. Given the very low probability of actually getting any significant reward, it's interesting how many well-known names took part, but perhaps also unsurprising that many entries look like they were dashed off in a spare lunch-break.

One thing that strikes me about the entries is the proportion which adopt a modern or futuristic approach. I believe the competition identified the need for station footbridges which would link railway platforms in both a new-build context, and also upgrades to existing stations, some of them heritage settings. Network Rail included examples of historic lattice-truss bridges in the material they supplied to entrants, but very few designers submitted ideas which appear adaptable to different settings. There were quite a few entries with a latticework theme, but hardly any which looked adaptable to many situations.

Another thing that jumps out is that this competition probably created a significant learning opportunity - assuming (from the quality of the design images) that many of the entries will have been prepared by younger professionals, it must have been a marvellous opportunity to test out their design and illustration skills.

Many of the entries are impractical, even amongst those where an engineer is named as well as an architect. However, I think it's clear that a good proportion of entrants did understand that this was a contest about ideas - the more pragmatic looking entries generally didn't make the longlist.

I can strongly recommend spending a few minutes checking out the competition website. I'm only going to include the winning, highly commended and long-listed designs here, but although there's a fair bit of dross, there are also quite a number of thought-provoking concepts, and one or two interesting styles of illustration.

Winner: Gottlieb Paludan Architects / Strasky, Husty and Partners Ltd
The winning design is beautifully presented and highly minimalist in its conception: a staple-shaped deck below a staple-shaped roof, modular and suitable for a variety of spatial arrangements.

Highly Commended: Hawkins\Brown / WSP
Like the winner, this is a modular, adaptable design, but with the structure and architecture secondary to the potential for a bridge as a social and commercial space. It's a smart, enticing idea, perhaps well-suited to some urban locations but over-ambitious for most other sites.

Long list (selected images only: see competition website for more)

Luca Poian Forms, UK with Soluxn Ltd

Weston Williamson + Partners, UK with AKT II Ltd

Atkins Architecture, UK

 PHASE3 Architecture + Design, UK with AKT II Ltd

Miguel Costa, Andy Fisher, Melanie Davison, Priscille Rodriguez & Jan Verhagen

CF.Architects, UK with Cake Industries

Softroom, UK with Eckersley O'Callaghan and Inverse Lighting

[Y/N] Studio, UK

 Xing Design Studio, People's Republic of China

 Pelizziarchitettura, Italy

 Squire and Partners, UK

 Marks Barfield Architects, UK with COWI

 Sweco Architects, Sweden with Sweco Civil and Sweco Structures

 Method Architecture, UK

 Kashdan Brown Architects Ltd, UK

 AWW, UK with Mott MacDonald

 Metropolitan Studio of Architecture, Pakistan

 Fereday Pollard Architects, UK

"Tower Bridge" by Harry Cory Wright

This lovely new book is part of a series of "pocket photo books", and is published alongside books on the Barbican Centre and Trinity College Library, Dublin. Harry Cory Wright is a photographer better known for his landscape photographs, who applies his sensibility to buildings for these small-but-sweet volumes.

Tower Bridge (Thames and Hudson, 176pp, 2019, amazon.co.uk) measures 17cm x 12cm and features 120 images of this iconic London bridge. There are some similar photographs in Tower Bridge: History - Engineering - Design, which I reviewed recently, displayed there at larger size, but I don't think the pocket format detracts from Wright's images at all.

Unsurprisingly, the pictures have something of a landscape sensibility. Very few show the bridge in its surroundings, but several show the surroundings viewed from within the bridge towers or walkways. Most of the photos show details of various sorts, viewed in a way which emphasises shape, colour and texture.

People are notable by their complete absence, even in images of the control cabin and visitor areas.

This makes an opening interview with Chief Technical Officer Glen Ellis feel like a stray presence from another book, some kind of ghost in the machine (although not in the Cartesian sense). Other than this interview, Wright's book is all machine and no ghost.

There are relatively few photos of the exterior of the bridge, and especially few of the stonework cladding, which is perhaps a shame as many parts of it are exquisitely detailed. However, Tower Bridge makes up for it with everything else that is included.

There are some fascinating images of the interior of the towers, glimpses of steel framework peeking out between stone and staircases. Rivets appear, and then reappear repeatedly.

There are some great images of well-preserved control gear within the bridge operator's cabin, and of the bridge machinery, both operational parts as well as the preserved but now motionless steam engines. The epic bascule chambers appear, but so also does the inside of the accumulator tower, which is not something I've often seen photos of.

Towards the end, there are some particularly nice photographs of small machinery parts, valves, cogs, regulators and the like, as well as workers' tools and shelves full of spare nuts and bolts.

The reader is left to make of it all what they will. Some brief information is given for each photograph in a section at the end, for the curious to pursue.

What stood out for me is the extent to which Tower Bridge really is one of our greatest surviving examples of Victorian engineering, notable for assembling in one place such a variety of interesting parts. It is extremely well cared for, and if it has been substantially altered then that is generally very well hidden.

Obviously, this is a book which should appeal to anyone interested in architecture and engineering, but also admirers of fine photography. The price and size also make it an affordable gift. I very much enjoyed it.

"Tower Bridge: History - Engineering - Design" by Kenneth Powell

Tower Bridge: History - Engineering - Design (Thames and Hudson, 192pp hardback, amazon.co.uk) has recently been published to mark the occasion of the bridge's 125th anniversary (which falls on 30th June this year).

The bridge is one of the most iconic and memorable in the world, and it certainly merits this excellently researched and beautifully presented volume.

The title is a good guide to the contents, which emphasise the achievement of the engineers involved and avoid the temptation to focus on the bridge as an architectural artefact.

The book starts out not with the bridge but with the River Thames itself, the earlier river crossings, and the role of the Pool of London as a key part of the city's port facilities prior to the construction of new docks at the Isle of Dogs in the early 19th century. Setting the tone for the rest of the book, this section is copiously illustrated with old photographs, plans and paintings.

Until the Dartford Crossing was finished in 1991, Tower Bridge was the last bridge across the Thames before the sea. Prior to its completion in 1894, that honour had been held by London Bridge for over 600 years.

As well as discussing the history of several of the key Thames crossings (both bridges and tunnels), the book features several that were never built, such as George Dance the Younger's 1800 idea to replace London Bridge with two parallel bridges, and Thomas Telford's 1801 proposal for a huge cast iron arch.

This is all interesting, but the story of Tower Bridge really began in the 1870s. London Bridge was increasingly congested and a committee was established by the City Corporation to investigate the possibility of a new bridge or subway. Numerous schemes were developed, some by well known engineers such as Joseph Bazalgette and Rowland Mason Ordish, and Powell's book covers these well, including some great illustrations of what now look like quite absurd ideas.

The twin bascule solution was originally proposed by City Architect Horace Jones in 1878, and is shown in detailed original drawings included in the book. This was a drawbridge design, with ornate towers helping to support an arch from which, in turn, the bascules were slung.

The involvement of engineer John Wolfe Barry in the project from 1884 led to the change to a design essentially similar to what was eventually built, with suspended side spans anchored to two elevated, horizontal tie girders, which eliminated the risk of the original arch being struck by tall ships and also served as walkways.

Powell's book does well to cover the many key individuals who were responsible for the bridge's design and construction. These include John Jackson, the lead contractor; William Arrol, whose firm fabricated the steelwork (most of it hidden behind the tower cladding); and William Armstrong, whose firm supplied the hydraulic operating machinery.

Horace Jones died in 1887, a year after the laying of the bridge's foundation stone, and the task of preparing the architectural detail drawings fell to George Daniel Stevenson, who later established his own architectural practice. Several of Stevenson's beautiful drawings are reproduced in the book, along with a handful of engineering drawings and plans. I'd happily have seen more of these, but the book is judicious in its choices.

After describing the architecture, structural engineering and construction work, the book devotes a full chapter to the machinery and operation of the bridge, with more excellent photographs and diagrams. The engineering aspects are well-explained, and I think the level of detail given is about right for a lay-readership - informative without being too extensive.

A chapter towards the end of the book addresses Tower Bridge's life following construction and its status as an icon, although I think there was more that could have been said here (compare, for example, Peter Spearritt's book on Sydney Harbour Bridge). The Tower Bridge clone in Suzhou, China, doesn't even get a mention!

The final chapter discusses a few of the people involved in the bridge during its operational life, such as the various Bridge Masters, and although this is very welcome I think it would have been better to integrate these tales into the body of the book. There are also chapter notes, a bibliography and helpful index.

Overall, this is a genuinely excellent book about a bridge which certainly merits this level of in-depth attention. In addition to the historic images, there are many very high quality photographs of the bridge today, which make the book a joy to look through. It should certainly appeal to bridge enthusiasts, but more widely to readers interested in London, architecture and engineering.

Related posts:

• Tower Bridge (with links to other resources)
• Tower Bridge ... some musings (on the rarity of stiffened suspension "cables")

"Aqueducts and Viaducts of Britain" by Victoria Owens

This is the second of two books about bridges published this month from Amberley Books. I featured "Britain's Greatest Bridges" by Joseph Rogers in my last post.

"Aqueducts and Viaducts of Britain" by Victoria Owens is 96 pages long and well-supplied with recent colour photographs, plus a few older illustrations. The book focuses on two centuries from 1760 to 1960, a prolific period of bridge construction driven first by the canals, then railways, then roads and motorways. There are, of course, older structures which could be considered viaducts, but Owens notes that the very term 'viaduct' is a reasonably recent coinage, introduced by landscape designer Humphrey Repton in 1816.

If Rogers' book on Britain's greatest bridges necessarily skips along the surface of its subject without ever getting in too deep, Owens' book is the precise opposite, submerged in its topic from the first page (there is no introduction) and only occasionally pausing to return to the surface for breath.

Within the first three paragraphs the book dives straight into the tale of James Brindley's Barton Aqueduct, Britain's first navigable aqueduct. Owens is something of a Brindley specialist, so the start of the canal age is covered well, although disappointingly the Barton bridge's successor, the remarkable and unique Barton Swing Aqueduct is given only passing attention. In general, it's fair to say that the book is noticeably more thorough in its coverage for the early part of the period covered.

The first four chapters of the book are split equally between early aqueducts and viaducts, including structures such as the Kelvin Aqueduct, Lune Aqueduct, Stanley Ferry Aqueduct, Sankey Viaduct, London and Greenwich Railway etc. A fifth chapter tackles problems that the designers and builders encountered, such as how to create skew spans, prevent scour, and mollify recalcitrant landowners: quite a variety of challenges!

The sixth chapter addresses the use of timber and iron, with wooden structures such as Ouseburn Viaduct, Brunel's Cornish railway viaducts, and Barmouth Bridge. Metal viaducts include Tyneside's High Level Bridge, Crumlin Viaduct, and Bennerley Viaduct. As in the earlier sections, many of the structures featured are less well known than those I have highlighted here.

Chapter 7 is the odd-one-out: a "case study" of the viaducts of the Settle to Carlisle Railway, masonry viaducts built in the 1870s, some in spectacular countryside. The best known structure is the Ribblehead Viaduct. Chapter 8 discusses the estuarial crossings of the Solway, Tay and Forth, while the final chapter features a very much abbreviated range of more recent concrete and steel bridges. The book concludes with a helpful bibliography and index.

Generally, the book is well written, well informed, and contained much that I did not already know. It tackles the history of each bridge effectively, and is confident in its description of architectural and engineering aspects. However, it jumps from bridge to bridge too rapidly, and would have benefited from putting its facts into a wider context. It's a little breathless at times.

It's probably not a book for the very general reader, but one for bridge enthusiasts, or those with a specific interest in canals, railways, and transport architecture.

Further reading:

• Interview with the author

"Britain's Greatest Bridges" by Joseph Rogers

Two books published this month from Amberley Books may be of interest to readers: "Aqueducts and Viaducts of Britain" by Victoria Owens and "Britain's Greatest Bridges" by Joseph Rogers. Both books are 96 pages long and well illustrated in colour. I'll cover the Rogers book in this post, and the Owens book next time.

I think it's best not to get hung up on the title of "Britain's Greatest Bridges", which begs questions from the outset. The book is set out in 40 chapters, each documenting a bridge ranging in date from the Tarr Steps up to the Queensferry Crossing. Many of the choices are shoo-ins: Royal Albert Bridge, Tower Bridge, Iron Bridge, Severn Bridge, Mathematical Bridge etc. But there are plenty of surprising absentees: Union Chain Bridge, Kylesku Bridge, Ballochmyle Viaduct, Pontcysyllte Aqueduct, Tyne Bridge, Grosvenor Bridge, Maidenhead Railway Bridge, Bideford Long Bridge, Glenfinnan Viaduct, Craigellachie Bridge - the list of aggrieved runners-up could be quite long. Just think of the book instead as "My Favourite British Bridges", and that's fine.

The book is weakest in the modern era. Do Itchen Bridge (span 125m) or Kingston Bridge (143m) really deserve to feature ahead of the mighty Orwell Bridge (190m)? None of the excellent concrete motorway bridges of the 1950s/1960s appear, and the selection of modern 'architectural bridges' is at best idiosyncratic (London Millennium Bridge, Salford Quays Lift Bridge, Scale Lane Swing Bridge, rather than Gateshead, Forthside, Castleford, Infinity, the Rolling Bridge etc). Some choices are a genuine surprise, most notably the Steampipe Bridge at the University of Birmingham.

Rogers is no bridge expert, but has clearly spent plenty of time researching his subject. It's a book for the non-specialist, someone with an interest in transport, history or architecture. A general reader should come away with an understanding of quite what a splendid set of structures this country can boast. From that perspective, I think the willingness to depart from the obvious is a positive feature. 96 pages sounds short, but I thought it was a reasonable length and appropriate to the subject matter.

The illustrations are well chosen, supplementing photographs with drawings, old postcards and other historic images, although some of the photographs are gloomy, lack contrast and have not reproduced well.

For the specialist, it's not a book I can especially recommend: there are no references or index, and several attempts to explain the structural engineering of specific bridges are clumsy and in some cases a little misleading. Indeed, generally the bridge is strong on historical and geographical anecdote, but weak on engineering and architecture. No editor is credited, and that shows in the sometimes clunky prose and occasional grammatical errors.

On balance, then, this is not one of "Britain's Greatest Books about Bridges", and definitely one for the general reader rather than a dyed-in-the-wool bridges buff.