30 July 2018

"China's Unique Woven Timber Arch Bridges" by Zhou et al

I don't normally make a point of mentioning technical papers on this blog, but maybe it's something I should do from time to time. I have previously wondered about putting together a semi-regular roundup of papers that might be relevant or interesting to my readers. However, I don't want to make more work for myself, so this may only very rarely happen!

I did think that this paper was worth drawing to wider attention: "China's unique woven timber arch bridges" (Zhou, Leng, Zhou, Chun, Hassanein and Zhong, Proc. ICE - Civil Engineering, August 2018).

This gives an overview of timber bridges in China of a type that dates back over 1000 years. I first properly encountered them in Ronald Knapp and Chester Ong's excellent book Chinese Bridges, which presents several bridges from the Zheijang and Fujian regions. The design and construction of these bridges is considered important enough for them to be included on UNESCO's Intangible Cultural Heritage List since 2009. A historic example, the Rainbow Bridge, is illustrated on the Song Dynasty painting Along the River During the Qingming Festival (~1085-1145), pictured above.

Nearly 100 of these woven timber arch bridges survive. Several have fallen victim to disaster through fire or flooding, including at least one of the bridges featured in Knapp's book. However, the construction skills have undergone a revival, such that some of these bridges have since been rebuilt. Indeed, the paper lists some 19 woven arch bridges which have been rebuilt or newly built since 1999.

The essence of these bridges is the structural form of a woven polygonal arch, which is described in detail in the paper, including several construction photographs. It consists of two sets of arch members which alternate across the width of the bridge, so that there are two superimposed polygons. These are locked together by transverse timbers, creating a triangulated system which in one way behaves not like an arch, but like a beam. However, it must also behave as an arch, as the main timbers are carefully butted together to be able to transmit axial load.

The paper in the ICE Proceedings is a short (6 pages) but very clear and useful introduction to these amazing bridges, and definitely worth a read if you have access to it. In case anyone would like to learn more about the woven arch bridges, I've collected a set of links to more detailed technical papers at the bottom of this page.

It wasn't until several centuries later that a similar bridge design was developed in Europe by Leonardo da Vinci. His design is discussed in a 2004 paper by Ceraldi and Ermolli, which compares da Vinci's design to the earlier Chinese bridges. Da Vinci's solution does not use the butted timbers, and is an open frame rather than having many alternating arches all immediately adjacent to each other.

Further information:

24 July 2018

Awards shortlists announced

The shortlist has been announced for the Structural Steel Design Awards 2018. Bridges projects on the shortlist include:
There are also several bridges featured in the shortlist for the British Construction Industry Awards 2018:
  • Chapel Street Bridge upgrade, Salford
  • Highbury Corner Bridge replacement
  • M4 River Usk Bridge Strengthening and Rehabilitation
  • Mersey Gateway Bridge 
  • Queensferry Crossing
  • Somers Town Bridge
  • The Ordsall Chord
The BCIAs also shortlist Leeds Flood Alleviation Scheme and London Wall Place, both of which have interesting bridges as part of the wider projects. There may be others, it's not always easy to tell from the scheme names.

I've included links to structures that I've previously featured here. I will be reporting on the London Wall Place walkways soon as well. Hopefully I can visit some of the others some day.

Winners for both the above awards schemes will be announced in October.

Finalists have also been announced for the European Steel Bridge Awards, with a winner to be announced in September:
  • The Railway Bridge line Hohenau-Prerov, Czech Republic
  • Rethebrücke, Germany
  • Loftnesbrui, Norway
  • Årstabron, Sweden
  • Parkbrug Spoor Noord, Belgium
  • Footbridge for Pedestrians, Cycles and Reduced Mobility, Luxembourg
  • Jungle Pedestrian Bridge, Norway

"Samuel Brown and Union Chain Bridge" by Miller and Jones

Union Chain Bridge is the oldest suspension bridge in the world which still carries vehicular traffic. Opened in 1820 to a design by Captain Samuel Brown, it is remarkable that it has survived so long, especially considering that so many of Brown's other bridges failed early in their lives. The bridge will reach its bicentenary in two years time, and the publication of this book is therefore timely.

Samuel Brown and Union Chain Bridge (Friends of the Union Chain Bridge, 306pp, ISBN 978-1-5272-1616-7) is the end result of extensive research by architect Gordon Miller, commenced in the early 1970s. Most of the content has not seen print before, although Miller published a paper in the ICE Proceedings in 2006 which summarised some of the Union Bridge story. Sadly, Miller passed away in February this year after completing this book.

The first, and lengthiest, section of the book explores Captain Samuel Brown's career, first as a naval officer and then as a pioneering supplier of iron chains. Initially, he developed chains for use in the navy as anchor cables and rigging. In 1813, he built an experimental 100-foot long suspension bridge at his Millwall chain factory, which was visited by eminent engineers such as Rennie and Telford. This led directly to the use of chains to suspend the Union Bridge, and soon to many more structures, principally built in the period from 1820 to 1832, with Brown's last bridge built in 1834. 

Miller's book recounts far more detail on Brown's many bridges than has been published anywhere before, drawing in depth on the surviving archive papers. However, this lengthy section of the book is not well structured, with no subheadings to help identify individual structures, and a number of digressions. The material is also in some cases curiously incomplete - the best known previous survey of Brown's works was in Emory Kemp's 1977 paper, which although briefer than this new book included some details which Miller omits. A useful chronology of Brown's work can be found at Engineering Timelines.

Comparing Miller's account against other books and papers relating to Brown, I'm left with as many questions as answers. Some other accounts report that Brown won the Union Bridge contract in competition with North Shields chain-maker Robert Flinn; elsewhere this is said to relate to a proposal for Norham Bridge circa 1817-1818. Miller's book does nothing to clarify the matter, with Flinn barely mentioned at all and no reference to any competition.

There are also unfortunate errors, such as citing Brunel as the designer of the Menai Suspension Bridge. These are not errors of knowledge, but can be put down to the absence of any kind of editor or proof-reader. This also explains the poor and inconsistent structure to the book. There is no kind of referencing throughout, and coupled with the other flaws, I have to say that for any serious student of bridge engineering history, this makes the book very difficult to trust. It is a terrible missed opportunity.

The lack of referencing means that previous documentation on Brown and his works is largely ignored: Kemp's paper is barely acknowledged, Day's papers are ignored entirely, as is Paxton's paper, which is a shame as it includes a useful numerical appraisal of the strength of Brown's chain designs, putting his practice into the context of what his contemporaries were doing.

The core of the book is an account of the Union Chain Bridge itself, its design, construction and opening as a toll bridge. Much of this is drawn from the records of the bridge trust, and it is thorough and informative. As is the case throughout the book, a great deal of contemporary record material is reproduced directly, including correspondence, images of the original bridge drawings, and Brown's 1817 patent. It's thorough, but sometimes a mixed bag, with many pages given over to exact reproductions of primary sources.

There is also a great deal of information on the bridge's history post-construction. This section includes an excellent set of sketches and details which illustrate how the bridge deck was modified on numerous occasions. Many of these were drawn up at the time of the bridge's major refurbishment in 1974.

Correspondence between the bridge trust and their consulting engineer at various stages is included, reporting continuing doubts about the strength of the bridge which had never really gone away since its original construction. The bridge's south anchorage was strengthened at the time of construction, and the north anchorage in 1902. The saddle details were a perennial problem: at the outset, a roller arrangement was provided to address thermal expansion, but the chains were allowed to rub on the edge of their support, and the hidden nature of the saddles inevitably led to progression of unseen corrosion at various stages.

I think that anyone looking for an in-depth understanding of 19th century bridge engineering history in Britain, or anyone with a deep interest in the history of suspension bridges, will regard this book as an essential purchase. However, it is grievously let down by the lack of any intervention from an editor, and the lack of proper referencing. For any more casual reader, the article at Engineering Timelines is a good enough introduction to the subject, and I can't recommend this book to them.

Further reading:

22 July 2018

Welsh Bridges: 16. Footbridge at Devil's Bridge

For the last in this series of posts on bridges in Wales, I travelled down the valley below Devil's Bridge, following the Devil's Bridge Falls woodland walk.

At the lowest point of the walk, a small wrought iron footbridge carries visitors across the River Mynach before they climb back uphill to the main road.

The footbridge has been Grade II Listed since 2005. A plaque on the bridge states "Aberystwyth Foundry 1867. Thos Stooke Engineer". There doesn't seem to be any further information on who Stooke was, or which foundry built the metalwork.

The bridge is has two highly arched truss girders, each in double-Warren truss configuration. The upper and lower chords of the trusses are quite slender. More modern anti-slip flooring has been added at some stage, I'd guess mainly for durability reasons.

It's a pleasant bridge but the real attraction here is the scenery, with a cascade of waterfalls totalling 91m in height.

Further information:

18 July 2018

Welsh Bridges: 15. Devil's Bridge

So, Devil's Bridge, we meet again.

Well this is a different Devil's Bridge to last time. Two down, many more still to go!

Devil's Bridge (or in the local tongue, Pontarfynach) is one of the better known tourist attractions in the Aberystwyth area. Anyone can cross the bridge, as it carries a public road, but to see it properly requires payment to access private land. In addition to the bridge, this gives access to a very scenic woodland walk, and is well worth the price of admission.

The legend that gives this bridge its name is the same or similar to most other Devil's Bridge tales: an old woman's cow somehow crossed over the river Mynach, and she couldn't get it back. The Devil offered to build a bridge in return for the first living soul to pass across it, and the old woman agreed. She threw some bread across the bridge, and her dog ran after it. The Devil, having expected a higher price, had to be satisfied with the dog.

What I learn from this legend is that the old woman was pretty smart to give up the dog in return for getting her cow back. It must have been a very impressive cow to have jumped across the River Mynach gorge before the first bridge was built.

There are three bridges here, each one built above its predecessors. It goes one better than Rumbling Bridge, in Scotland, in that respect.

The lowest span is medieval, generally thought to date back at least to 1188, and comprises a pointed masonry arch sitting astride a remarkably deep cleft in the local rock, which contains the River Mynach (Afon Mynach). The most widely-held view seems to be that it was built by the monks of Strata Florida Abbey.

In Gwyndaf Breese's book on Welsh bridges, he suggests that the bridge reported by a traveller in 1188 was a "rickety wooden bridge", and that the stone span may have been built a century later.

Other than for its age and situation, it is relatively unremarkable. The arch barrel consists of thin bands of stone, springing directly from the rock. The profile of the barrel is noticeably distorted and unsymmetrical.

Breese quotes Jervoise in suggesting that the lowest bridge was widened or rebuilt at some stage. Jervoise's comment was that pointed arches were not in use in the 12th century, and the span must therefore have been a later reconstruction. I'm no expert but I don't think that is conclusive: the pointed spans in the medieval Exe Bridge are believed to be original, so why not here?

In 1753, a second bridge was constructed, a segmental stone arch spanning 32 feet. This bridge was later modified, with the height of its spandrel walls increased in 1814 to reduce the steepness of the highway approaches. It looks like you can see evidence of this in the banding of the horizontal stones in the spandrel walls. The ornate cast iron parapets were added at this time.

Buttresses at either ends of this span appear to have been added later. At one end of the bridge, the arch appears to spring from a higher point than at the other. Instead, it seems that the original springing is hidden within the masonry buttress, which continues under the arch barrel.

The third bridge was built in 1901 to a design by the County Surveyor Roderick Lloyd. Masonry abutments were built up to support steel lattice girders spanning 60 feet and carrying a 20-foot wide roadway.

This was substantially modified in 1971, when the castellated plate girders visible today were inserted along with a concrete deck slab. It looks to me that the parapets were designed to retain the appearance of the lattice girders, but clearly what's there now could not have been the original spanning trusses as there are no upper or lower chord members.

The newer girders are supported at one end on the abutment of the middle bridge, and at the other end on steel portal frames carrying the load to either side of that span. This was obviously an unfortunate period in the life of Devil's Bridge: the position, appearance and level of the new girders were all entirely unsympathetic to this span's predecessors.

Further information:

15 July 2018

Welsh Bridges: 14. Llandeilo Bridge

Completed in 1848, the mighty Llandeilo Bridge is one of the largest masonry arch spans in the United Kingdom. By my count it takes third place behind Grosvenor Bridge (61m / 200 ft, 1832) and Ballochmyle Viaduct (55m / 181 ft, 1848), making it the longest masonry span in Wales. (I'm happy to be told otherwise if there are any bridge spods out there somewhere.)

The Grade II* Listed bridge is said to span either 143 ft or 145 ft (take your pick!), and to be 26 ft or 10.1m wide (again, you choose!).

However tall and proud it may stand today, it had a difficult beginning.

The first bridge on this site was a seven-span arch bridge, which partially collapsed in 1795. The failed centre spans were replaced with a timber structure.

According to some accounts, the bridge was replaced in the early 1800s by a narrow three-arched bridge, which proved too narrow for traffic, although not all histories seem to agree (for the most thorough story of the bridge's past, see Llandeilo Past and Present).

County bridge surveyor William Williams was appointed to design a replacement in 1843, estimating the cost of his design to be £10,000. Builder Morgan Morgan was appointed on a contract price of £5,870.

The cash ran out while Morgan was still constructing the bridge foundations, and work was further set back when a flood destroyed part of the works. Edward Haycock took over the scheme, completing the bridge in 1848 with a total expense of £22,000.

Despite these difficulties, it was a huge engineering achievement. The causeway to the south is a substantial structure in its own right, giving a total length of 111m for both causeway and arch. The town of Llandeilo sits some height above the River Towy and its flood plain, and a lengthy ramp was required to allow traffic to enter the town at a suitable level.

The causeway is pierced by a smaller cattle creep, span which like the main span has an elliptical profile. On the main arch, this choice was driven by the span dimensions and height of the roadway. The cattle creep arch is described elsewhere as a flood arch, but I doubt it adds greatly to the bridge's flood capacity.

The main arch is described as having long, thin voussoirs, but as can be seen close up, they are in fact made up of short(ish) stones with thin ashlar joints.

Looking at the bridge today, it's impossible not to be impressed by the sheer ambition of this small town and those involved in building the bridge. It's difficult to know whether they could have fully appreciated the nature of the task they were taking on. It's interesting to think what would have happened if the entire project had been abandoned after Morgan's failure.

Further information:

11 July 2018

Welsh Bridges: 13. Llandeilo Suspension Bridge

This is the first of two bridges spanning the River Towy that I visited in Llandeilo, a small village in Carmarthenshire.

I've found very little hard information on this bridge. The Bridgemeister website lists it as built in 1911. The same date appears elsewhere, along with an indication that the bridge was built to commemorate the coronation of King George V.

It was originally named the King's Bridge, although nicknamed the Swing Bridge in more recent times (as is the case with many suspension footbridges).

The Buildings of Wales: Carmarthenshire and Ceredigion agrees that the bridge was built for the coronation in 1911, gives the span as 144 ft (44 m), and states the bridge was built by David Rowell and Co. That makes it the third and final Rowell bridge I visited on this trip, the others being Llanstephan (1922) and Elan Village (1904).

This is the least well-preserved of the trio (which is saying something given the condition of the bridge at Elan Village).

It's not entirely clear how much of the original structure remains. The cables look like they may be original, but the hangers and parapets definitely are not. I didn't get a close look at the bridge deck.

The original steel lattice towers, of a design typical of Rowell's bridges (compare the Howley bridge), have been almost entirely encased in concrete, with just part of the upper cross-bracing left exposed, along with the tower finials (another classic Rowell visual signature).

The concrete has preserved the bridge for a time, but at a cost: future replacement of the cables is now made very difficult, and eventually the day will come when the only option is to replace the entire structure.

Further reading:

09 July 2018

Network Rail Footbridge Design Ideas Competition

The UK's national rail network owner, Network Rail, recently announced an international Footbridge Design Ideas Competition. The competition is being administered by the RIBA Competitions office, and seeks architects or engineers (or teams of both) to present their ideas no later than Tuesday 18th September.

The organisers ask for ideas which are "innovative, challenge presumptions and raise expectations for the quality of future designs". I get the impression there is a perception that design quality in the UK railway network is often poor (I think this is true), and an ambition to see if anything better can be suggested.

Entrants must be either professionally qualified, or students. There is a nominal registration fee of £50 for professionals or £25 for students, presumably to minimise the number of contributions from complete jokers. Submission requirements are not especially onerous, being two A2-sized digital layouts, three images, and a declaration form.

There is only one prize, a "Design Fund" worth £20,000 which is expected to be awarded to the best entry, although could presumably be split. There is no potential design contract being dangled, with Network Rail essentially purchasing the ideas to use as they see fit with no further input from the winning competitor.

For the promoter, this is a cheap way of generating fresh and imaginative proposals. For competitors, it's a chance to freshen up their creative muscles, enjoy the pleasure of collaboration, and hope for a bit of positive publicity.

What's notable about this contest is that it is not Network Rail's first attempt to improve design quality in this area. They held a shortlisted design competition a few years ago, but I don't think much came of it.

They are also, in parallel with the new competition, looking to procure a consultant designer to develop a new footbridge design, again with a substantial architectural contribution. This is not announced publicly, only to Network Rail's pre-registered suppliers. The successful designer will be appointed through a conventional price / quality bid, and given the opportunity to work with the client and relevant stakeholders to come up with a new design or range of complementary designs.

It doesn't feel very joined up, but represents well the issues that large public bodies can have with procurement of creative design. Open competitions tend to generate more imaginative ideas, but may highlight teams who the client would find difficult to work with in follow-on stages; more direct procurement will lead to more predictable outcomes but gives the advantages of control. I think there is no perfect answer to this dilemma.

08 July 2018

Welsh Bridges: 12. Dolauhirion Bridge

One of the best known Welsh Bridges is Pontypridd Bridge, designed by William Edwards, and completed in 1756 (after a series of false starts). This tall arch with its circular openings near the ends of the arch is so closely associated with Edwards that it is, apparently, sometimes just referred to as the William Edwards Bridge.

Edwards was not a "born" bridge engineer, having been first a clergyman and then becoming a self-taught mason and engineer. In addition to the Pontypridd Bridge, he completed a series of other bridges, including the Dolauhirion Bridge depicted here, from my recent visit. It was completed in 1773 by William's son Thomas.

You can easily drive over this Grade I Listed bridge (and Scheduled Ancient Monument) without really knowing it is there. It is smaller and less impressive than its Pontypridd cousin, but also has circular openings in the spandrels, and is very well suited to its place on the River Towy. The prolific chronicler of ancient bridges, Edwin Jervoise, described it as "the finest bridge over the upper part of the Towy".

Different sources report the span as variously 30m or 25.6m (84 feet). The circular holes (oculi) are  reported to be 2.4m (8 feet) in diameter.

Both the arch barrel and the oculi are formed from a single layer of large stones, while the spandrel walls are faced using less well-ordered and much thinner stones.

At some point in its history, the bridge was strengthened with a reinforced concrete saddle. I don't know whether the bridge was waterproofed at this time, but the underside of the arch barrel is thickly encrusted in mineral deposits resulting from many years of water seepage.

This is not by any standard a magnificent, monumental bridge; it is relatively understated, but attractive and appropriate for the location. Given the extent of surrounding vegetation, the oculi do little to lighten the overall appearance.

Seen from below, the bridge's lateral slenderness is the most obvious and impressive feature.

Further information: