08 November 2015

"Bridging the Dutch Landscape: Design guide for bridges"

This book is nearly 10 years old now, having been published in 2006. It was written by Christa van den Berg, an architectural journalist, with Gerhard Nijenhuis of design firm ipv Delft, and seems to have now been made available online in its entirety (you can also find a PDF version at www.overbruggen.nl). However, that's no real substitute for holding the actual book in your hands, I think - it's available from amazon.co.uk and no doubt elsewhere.

The book distils the design experience of the authors, and is copiously illustrated, mainly with examples of ipv Delft's prolific work. They are an interesting firm, largely staffed by industrial design engineers rather than structural engineers or architects, and their work is united by a sense of functionality and straightforwardness. Even in their more prosaic short-span bridges, there is an effort to maintain design quality.

The book is targeted largely at novice bridge designers and their clients, taking a step-by-step approach to bridge design which is helpful for the specialist but largely aimed at others. The book's 160 pages open with a generic guide to bridge design, with chapters titled "What is a bridge?", "Bridge types", "Materials", "Bridge deck", "Railings", "Engineering aspects" and "Costs". Two projects are explored in detail to describe the design process, and a further 26 projects are shown in brief. The whole book is profusely illustrated with photography and drawings.

Most of the bridges featured are unspectacular in nature, and this is the book's greatest strength. Not every bridge is a landmark, or an opportunity to take advantage of a client's generous funding. Most bridges which are built are relatively small, relatively modest, and need to be highly economical. Due to their ubiquity, attention to visual quality on such bridges can have a large impact on the built environment.

One of the two main case studies is a set of 59 bridges for a housing development at Het Jeurlink, for which a family of bridge designs were created, small road bridges, foot and cycle bridges, very small bridges and one or two larger bridges. This gives a good example of how simple parapet designs can establish a consistent identity, and remain adaptable to a variety of needs.

Of the other bridges featured, there are as many that I dislike as that I like, but I still found that instructive - the sheer quantity of designs offers inspiration for what to copy as well as to avoid.

Experienced bridge architects will find little in here for them. I think a good audience for this book would include engineers, who need every bit of visual training they can get, and specialist suppliers of small bridges, who might be inspired to raise their own game a notch.

30 October 2015

"River, Railway and Ravine: Foot Suspension Bridges for Empire" by Douglas Harper

Here is a lovely work of special-interest history. River, Railway and Ravine (The History Press, 2015, 164pp) [amazon.co.uk] documents the suspension bridges of John and Louis Harper, Aberdeenshire fence-makers turned bridge-builders.

Between 1870 and 1910, the Harpers designed and built over 40 suspension footbridges, mostly in the UK, but also as far afield as India, Nepal, Estonia, South Africa and the West Indies. Few survive now, and I've only visited one, at Newquay, although there are bridges built by the Aberdeen firm of James Abernethy in which Louis Harper may have had a hand, such as those at Aberlour and Cambus O'May.

Descendant of the Harper family, Douglas Harper, has been researching his family's engineering history for some time, with much of it documented on the Harper Bridges website. Now, this excellent book offers far more detail on the family firm's achievements, and I'd recommend it to anyone with an interest in historical suspension bridges.

The Harpers were innovators in their field: early users of steel wire rope; developers of a specialist wire-tensioning device; and users of pre-tensioned cables at deck level to greatly increase the stiffness of their designs.

The book gives a good history of the family, and their work both in fencing and then bridge-making, and puts this in context with a chapter exploring other suspension bridge developments in the 19th century.

The main part of the book offers detailed discussions of every bridge built by John Harper, and his son Louis. These are accompanied by numerous well-reproduced photographs and drawings, both present-day and archival. The level of research presented is remarkable.

What makes the book a particularly enjoyable read is the personal touch, as the author has attempted to visit as many of the bridges sites as he could, even where long-since demolished. In particular, the tale of his trip to Nepal turns the book from a simple historical record into a narrative which brings the past very much to life.

13 October 2015

Welsh Bridges: 5. Barmouth Bridge

This is described as the longest estuarial bridge in Wales, and it's certainly the longest timber bridge in Britain, being a total of 731m long. It has carried the Cambrian coast railway across the mouth of the Mawddach Estuary, between Barmouth and Fairbourne, since 1867. There are 113 timber spans, comprising braced wooden trestles, and five metal truss spans at the northern end.

Originally, an opening span was included of so-called "cock-and-draw" construction, which reportedly took some 37 minutes for two men to open. This was replaced by Cleveland Bridge in 1900 with the present arrangement. The timber trestles have been entirely replaced at least once in their history, and were most recently refurbished by Network Rail the early 1980s.

The metal spans are an interesting arrangement. There are two bowstring trusses, which at first glance appear identical. However, one is a simply-supported span, and the other is a swing bridge supported from its centre on a pivot pier. Closer examination reveals that the swing span has vertical members above its pier which are not present on the other span, as you would expect, and I expect the detailed build-up of steel sections is also different.

The bridge has clearly not opened for some time (there's a photo of it open here). The opening mechanisms are in a state of considerable disrepair, and the rails across the bridge are now continuous across the span joints.

Only a single rail track passes over the bridge. The bulkhead rails are supported from longitudinal baulk timbers, which are held at the correct spacing by a series of metal struts and ties. Metal cleats hold the timbers in position on the main timber decking. On the metal spans, short lengths of longitudinal timber sit within "bath-tubs" in the metal bridge deck.

A timber footway passes along the eastern edge of the viaduct. This is a very pleasant walk, with fine views of the Mawddach estuary, but also a vital link between Fairbourne and Barmouth. There is an occasional passenger ferry between the two towns, but after the rail viaduct, the next crossing upstream is the toll bridge at Penmaenpool, which is only open during the daytime, and beyond that, the road bridge near Dolgellau.

A toll was levied on the footway since the early twentieth century, but this has recently been abolished.

At the south end, the footway slopes steeply up to the nearby highway, and Barmouth residents have established a campaign for a better footway connection.

The timber parts of the bridge are in fair condition, although there are a number of holes in the trackside decking which have been covered over with metal or GRP plates. From below, isolated areas of rotted or damaged timber can be seen, and metal fixings are severely rusted, as is only to be expected in a tidal estuary.

The condition of the metal spans is of greater concern, being extremely poor with little or no worthwhile protective treatment, and extensive corrosion. Network Rail have plans for a full refurbishment of the metal elements, which appears to be long overdue. This is not a busy railway line, and it must be difficult to justify the expense that properly maintaining this type of bridge should entail.

Walking over the bridge, it's hard not to speculate about the possibility of building a highway bridge nearby. When the Penmaenpool toll bridge is closed, the highway journey between Barmouth and Fairbourne takes about 17 miles, and even when its open it's still 14 miles. As the crow flies, the actual distance is only 2 miles, so a highway bridge would be of considerable benefit both to local residents, and to others passing north and south along the coastline. It would be an expensive endeavour, due to the need for lengthy highway improvements approaching from the south, and potential conflict with Barmouth harbour at the north end.

Meanwhile, the local council, which essentially "rents" the walkway from Network Rail for £30,000 per year, is under severe pressure to reduce costs and is considering closing the footpath. It's hard to argue that it should be more of a priority than many other hard-pressed council services, but unsurprisingly there is a great deal of opposition to closure, including an online petition with over 40,000 signatures.

I think this is a lovely bridge, of great engineering, historic and social value, and it would be a shame to see it closed or not maintained. It's not far from the site of Pont Briwet, another timber viaduct which, despite its Listed status, was recently demolished and replaced with a new concrete bridge. It would be a terrible shame for Barmouth Bridge to ever follow suit.

Further information:

03 October 2015

Welsh Bridges: 4. Penmaenpool Bridge

This privately owned timber road bridge dates from 1880, when it was constructed by the Penmaenpool Bridge Company Limited, under agreement with the Barmouth Harbour Trust. It crosses the River Mawddach in Wales, and provides a useful short cut between the coastal towns of Barmouth and Fairbourne during its opening hours.

Most spans are 20-feet, but the central span is 30-feet. This span was designed for possible conversion into an opening bridge span, in case a disused boat-building yard upstream of the bridge was ever re-opened, but this was never required.

The structure is a series of straightforward braced timber trestles, with a heavy deck of diagonally arranged baulk timbers. It appears to be generally in good condition, although several of the deck timbers are loose.

The bridge is operated as a private toll bridge, with prices of 20p for a pedestrian, or 70p for a motor vehicle not exceeding 1.5 tonnes in weight. The bridge is only open between 8.30am and 6.30pm, with tolls being collected from the southern end, adjacent to the bridge-owner's cottage.

It's a lovely spot to visit. The abandoned railway line on the southern edge of the river has been converted into a cycle and walking trail, Llwybr Mawddach. The former signal box is now a bird-watchers' hide, while the old railway station and platform are now part of the nearby George III Hotel. It's a splendid spot from which to admire the historic structures, landscape and wildlife.

Further information

21 September 2015

Bath Quays Footbridge Competition entries published

These came out a few days ago now, but I've only just had time to look at them properly.

This is a contest for a new £2.5m pedestrian bridge across the River Avon in Bath, organised by Bath and North East Somerset Council.

In May, six teams were shortlisted, and each given £5000 and eight weeks to develop a design. The teams are:

  • AL_A / AFA Consult
  • Flint & Neill / Moxon Architects
  • Grimshaw / Buro Happold
  • Heneghan Peng / Ove Arup
  • Marc Mimram / Webb Yates
  • Price & Myers / McDowell & Benedetti

Now, all six entries have been released, although anonymously. You can have fun, if you wish, trying to guess the designers! A winner was originally scheduled for August, but this is now expected to be in November.

Entry 1
This is a very curious design, a propped cantilever bridge (intended to minimise physical impact on the historic south bank of the river) fabricated from a series of extremely lightweight trusses. It's fiddly to the point of being finicky, and would make a fantastic climbing frame for the locals to explore. The truss members are all of stainless steel, but painted, which is a genuinely baffling idea.

Entry 2
Again, this is a structurally bold design, and one which makes use of the same basic principle: support the bridge from the north bank so as to reduce impact on the south bank. It's an unusual "cable-stayed" bridge, with a steel box girder deck which is boomerang shaped in plan, and supported by a mast on only one side. The normal cables are replaced by steel ribbons. I especially like the detailing of the balustrades on this design.

Entry 3
This entry comes with a name, the "zig-zag bridge", which describes its profile in plan. Architecturally, it is extremely restrained, so modest that the zig-zag is the barest nod to the need for the bridge to express something, anything. The money here has gone into expensive materials: stainless steel box girders and balustrades, a Bath Stone handrail, and a "precast granite" deck. I'm not quite sure what precast granite is, but it sounds expensive, anyway.

Entry 4
Captioned "Between history and modernity", the fourth design takes the idea of responding to a propped cantilever moment diagram as seriously as did the first, and with much the same logic. The bridge curves gently in span, and is supported by two Vierendeel girders, one on each edge of the bridge. These are shaped to provide almost a hinge at the point of structural contraflexure. They remind me a little of the Vierendeel ribs on Paris's Pont de Solferino, a Marc Mimram design. The designer has tucked the main supports away behind the edge girders, which would be implausible on anything other than a short footbridge.

Entry 5
Now here's a design that I quite dislike. I loved the basic image, an elongated Ikea-like picture frame, with ancient Roman ivy already growing over it, but I think the design fails under closer examination. It's a bridge with a tall central timber truss with footways either side, possibly intended as a Vierendeel but that's clearly impossible in timber at any useful scale. Diagonal steel bars and a support framework for the vegetation fill in the truss bays, making it impossible to cross from one side of the deck to the other.

Entry 6
The final entry is the most intriguing, at least in terms of its engineering. It's a half-through girder bridge, with twin steel girders constructed from perforated weathering steel plate. The perforations are layed out to suit the stress patterns in the girder, which is constructed of a series of steel segments. The segments are stressed together using stainless steel prestressing cables. It's technically fascinating, although I think it's perhaps the least sympathetic bridge to this particular site, and a concept which may be more appropriate elsewhere.

For your amusement, here are my guesses at the various designers. I'm not going to forecast the winner, but if I had a vote, it would go for Entry 6.

  1. AL_A / AFA
  2. Flint & Neill / Moxon
  3. Grimshaw / Happold
  4. Mimram / Webb Yates
  5. Henneghan Peng / Arup
  6. Price & Myers / McDowell + Benedetti

03 September 2015

Tintagel Castle: Shortlist announced

The organisers of the design competition for a new footbridge at Tintagel Castle in Cornwall, England, have shortlisted six out of one hundred and thirty seven entries. A winner is due to be announced early in 2016.

  • Dietmar Feichtinger Architectes with Terrell (France)
  • Marks Barfield Architects with Flint and Neill (UK)
  • Ney & Partners Civil Engineers with William Matthews Associates, Ettwein Bridges and Waagner Biro (Belgium)
  • Niall McLaughlin Architects with Price and Myers, and Max Fordham (UK)
  • RFR and Jean-François Blassel Architecte, with Engineers HRW, and WSP (France)
  • Wilkinson Eyre with Atelier One (UK)

They seem to have assembled some (mostly) impressive contestants, although a number of well-known bridge design specialists are notable for their absence. I certainly look forward to seeing the various designs unveiled in due course.