18 September 2012

Scottish Bridges: 52. Haugh of Drimmie Bridge

The final day of our Scottish bridges trip revolved around the bridges of the Justice family of blacksmiths, all built in the period from around 1820 to 1840. Five of their bridges are known to have been built, although the one at Clova Kirk in Glen Clova is long gone. Of the other four, we had already visited those at Crathie and Kirkton of Glenisla. The next bridge is in many ways the most accomplished of them all, at Haugh of Drimmie, near Blairgowrie.

This bridge spans about 32m across the River Ericht, and is 3.2m wide. It is Listed Category A. Its exact date of construction is not known but it was mentioned in the 1837 New Statistical Account of Scotland, with the following description:
"The only other object pertaining to this parish, which I shall mention as a matter of curiosity, is an iron bridge, which Colonel Chalmers of Glenericht, has thrown across the river, a little below his house. The bridge is supported by a stone pillar at each end, from which a direct span, not an arch, stretches across the whole breadth of the river. The bridge is of such wideness as to admit a passage for a carriage, with a foot tract on the side for travellers, the bottom or floor of both of which is covered with gravel to prevent alarm to man or beast. By this bridge, the Colonel has easy and elegant access to his property on both sides of the river, and also to the great road which runs from Braemar to Perth. The bridge was constructed by a Mr Justice in Dundee, and is well worth the notice of strangers."
While this hardly suffices to describe the bridge, it does offer a nice reminder of quite how compellingly strange it must have appeared when first built. In the 1820s and 1830s, a flat span bridge of any dimension was still a tremendous novelty. A few isolated suspension bridges had been built, but girder and truss bridges of any size were still to come.

The Haugh of Drimmie bridge has retained a definite strangeness today. Clearly, its deck has been altered over time, but the main structure seems to be original. It very closely resembles Justice's bridge at Crathie, with amazingly slender pylons, rod stays at a very shallow inclination, and a panoply of transverse and longitudinal bowstring ribs below the deck. Unlike its sibling, it was never strengthened with suspension chains, and also unlike its sibling, it continues to carry vehicles today, albeit with signs at each end declaring a weight limit of 2 tonnes. Given the extraordinary slenderness of many of its parts, particularly the pylon legs, I find this quite astonishing.

It lacks the rag-tag charm of the 1824 bridge at Kirkton of Glenisla, and was clearly a much more polished venture. Nonetheless, many individual features are essentially the same, such as the presence of curled ornamental brackets at the base of the pylon legs, the varied use of through-bolts and external clamps to connect the main span and anchorage rods to the pylons, and the presence of slender arched portals above the pylons.

The bridge deck is constructed in timber, with narrow timber "footways" which with their tall kerbs are an effective way of limiting the live load on the bridge. The kerbs also provide the primary vehicle containment, protecting the weak parapets as well as the hanger rods. Hidden below the deck there are scuppers at regular intervals which allow water to drain.

As with its sibling structures, it's only when you step back and consider quite how tiny the individual members are that you wonder quite how it has survived for so long. I think this is one of Scotland's finest historic bridges, and it deserves to be much better known.

Further information:
Updated 27 September 2012:
See the comments on this post for some very interesting additional information about this bridge.

17 September 2012

Sixth Street bridge designs published

In April, I mentioned a design competition for a US$400m replacement of Sixth Street Bridge in Los Angeles.

Three firms (out of nine) have been selected as finalists to develop design options, and their efforts so far were made public last week. Public consultations are happening today and tomorrow. A decision on the winner is due in early October.

Here are the designs (lots more pictures here). Click on any image for a larger version



Parsons Brinckerhoff

Quick reaction: The PB design is frankly bizarre, a bridge that looks like a twin arch (echoing the existing bridge) but is actually a very odd cable-stayed bridge. It's hard to see how it can possibly be economic for a bridge on this scale. The Aecom design, a Calatravesque extradosed bridge with a shot of gold bling (surely a Las Vegas feature, not a Los Angeles one) is likely to be the most economic to build. Visually, I like the style of the HNTB design, although the repeating arches away from the main river span seem to give it a grossness of scale that is not normally desirable in a city-centre structure.

What do you think? Post in the comments if you have an opinion!

13 September 2012

Scottish Bridges: 51. Kirkton of Glenisla Footbridge

On the third and final day of our Scottish bridge trip, we drove south from Braemar. We only planned to visit four bridges, but they included some of the best of the whole trip.

Our first stop was for a little footbridge spanning 18.9m over the River Isla at Kirkton of Glenisla. This was built in 1824 by John Justice Jr, whose work we had met the previous day at Crathie Suspension Bridge. The Justice family were blacksmiths, and everything about their bridge work was informed by that background.

It's hard to overstate the historical significance of this bridge. You won't find it mentioned in the normal books on bridge engineering history, but it is almost certainly the oldest unaltered reasonably pure cable-stayed bridge in Britain, and I think it might possibly be the oldest surviving example anywhere.

It was Listed Category B in 1971 (it's also an Ancient Monument), with the following brief description:
Footbridge. Wrot-iron suspension with wood decking and stone abutments. Arched approaches have plaques inscribed, "Jn. Justice, Dundee 1824". Picturesque.
That's both mildly inaccurate and utterly inadequate - I'll boldly suggest this is one of the most important historic bridges in the UK. Earlier bridges with stays had been built in Scotland from 1816-17 at Galashiels, Dryburgh and King's Meadows, but none survived for long. They were well-reported by Robert Stevenson in his 1821 article Description of Bridges of Suspension, so may well have been known to Justice.

In form, it is a twin-pylon single-span cable-stayed bridge. Three rod stays anchor each pylon leg to ground (varying in diameter from 11/16" to 7/8"), and four rod stays, each 9/16" in diameter, connect the main span to each pylon leg. Two of the span stays meet at midspan on each side of the bridge. There are several great diagrams at the RCAHMS website, but this one is perhaps clearest.

The stays provide the main structural support, but not the only one. Some of the rods in the bridge balustrades sag downwards, a little like suspension cables, and are anchored to the pylons in a manner which suggests they also help hold up the bridge. The sag is extremely shallow so it's hard to believe they contribute much.

The deck itself is astonishingly slender. There are two iron edge members below the timber decking, each a simple flat bar, and flat bar cross-members connect these at intervals matching the stay connections and parapet posts. The main edge members seem to serve the main function of providing the stays with a tension tie to react against. It's no great surprise to see that the deck has deformed over time and taken up a slightly twisted profile.

Much of the pleasure of seeing this bridge comes from realising quite how startlingly skeletal its structure is. However, as much pleasure comes from the myriad of small details, such as the way the stays are variously bolted through the pylons as well as connected to clamps passing around them. They give the clear impression that this was an entirely experimental bridge, with additional elements added one-by-one until the builder was satisfied it would not fall.

The parapets give the same impression, with a jumbled assortment of bars and flats thrown together around the main support elements.

The bridge forms part of the 64-mile Cateran Trail, a walking route which is named for cattle thieves who once roamed the area. The reason for construction of the bridge itself is now unknown.

Further information:

11 September 2012

Scottish Bridges: Second day summary

The second day of our Scottish bridge tour was nearly as busy as the first. Starting in Inverness and finishing in Braemar, we visited 14 bridges. They spanned approximately 250 years of bridge construction.

Here are links to all twelve:
Here's a map showing the locations of the bridges, our start and finish points, and the ground that we covered (click to see it at larger size):

10 September 2012

Scottish Bridges: 50. Falls of Gharb Allt Footbridge

I stumbled across the details of this bridge via Google while preparing for this Scottish bridge trip. It’s not a span I was previously aware of, and I don’t think it appears in any book about bridges to be found on my shelves. However, it certainly should do.

Nor is it well recorded on the internet: Aberdeenshire Council's Sites and Monuments Record doesn't feature it, and although it's Listed Category A, it achieved that status only in 2010.

The probable reason for its lack of renown is simply that it is very well hidden away in the private forests of the Balmoral Estate. It’s not signposted, and not very easy to get to.

For our trip, we had secured permission from the Estate to approach it on foot. I expect that Scottish land access rights actually render that unnecessary, but note that there’s no right to park a car on private land, so you may need to park some distance away if walking there. Another option is to book a place on a Balmoral Estate “safari”, as these sometimes include a visit to the bridge.

This cast iron footbridge was built in the time of Queen Victoria, and spans a watercourse which tumbles down through the Ballochbuie Forest and eventually out into the River Dee. It was built by Blaikie Bros in 1878 (also responsible for the mid-1880s refurbishment of Crathie Suspension Bridge, and the 1885 bridge at Abergeldie Castle).

It’s a very attractive ornamental iron arch, which would not be out of place in a park or estate garden.

The arch ribs are extremely slender, stiffened vertically by spandrel bracing intersecting in a diamond pattern. The main ribs are also cross-braced horizontally.

The parapets incorporate a repeating floral pattern, a level of ornamentation which I would imagine found more favour with Victoria and Albert than did the austere functionalism of Brunel's Balmoral Bridge.

It's a charming little structure, but what made it well worth visiting is its setting, spanning directly across the Falls of Gharb Allt.

I've seen more spectacular waterfalls on a private estate in the Western Highlands, but the scenery here is delightful, and the bridge offers a splendid vantage point from which to admire the turbulent river.

In the interests of safety, it's worth pointing out that the rocks next to the river are extremely slippery, so anyone seeking a good vantage point for photography should take care.

Further information:

09 September 2012

Castlemeads Footbridge Competition Winner

A design competition was recently organised by the Institution of Structural Engineers along with Gloucester Heritage Urban Regeneration Company for a new pedestrian bridge in Gloucester. Entry was limited to young structural engineers, graduate members of IStructE or a near equivalent. Twenty-six teams submitted entries.

The winning team was announced at the end of August as Matthew Myerscough and James Stewart, both of Cass Hayward. They received a £150 prize, and the hope that this essentially speculative footbridge proposal might actually one day obtain funding.

The winning design is for a curved deck, supported by a deep beam above deck level on the inner edge of the curve. It's highly reminiscent of Peter's Bridge in Norwich.

I've found two other designs online:

Elliott Wood

Raj Suhail

06 September 2012

Scottish Bridges: 49. Old Invercauld Bridge

Readers who’ve somehow stayed with me throughout this interminable series of posts on Scottish bridges may have noted a proclivity for metal footbridges of the 19th and 20th century, and a general lack of interest in the many masonry spans which actually make up the majority of the older bridges in the Scottish Highlands. The explanation is simple – I’m an active bridge designer, and I’m drawn to structures which I feel hold some kind of technological relationship to those that I design or wish to design.

However, the Old Invercauld Bridge could not pass without comment. There are two road bridges here, one which carried the old road to Braemar across the River Dee, and one which replaced it. Both are multiple span arch bridges. We didn’t stop to photograph the New Invercauld Bridge, but its older companion is a very striking structure.

The old bridge was built in about 1752 as part of Major William Caulfield's programme to build a network of military roads across Scotland. It's now a Scheduled Monument.

It has six spans of rubble masonry, with the spans varying from 10 feet to 68 feet. Huge flagstone-topped triangular cutwaters punctuate both faces.

In 1859, it was bypassed by a new three-span masonry arch bridge, built by J F Beattie at the instigation of Prince Albert. This then carried the Aberdeen to Braemar road, now the A93. The old bridge became part of the Balmoral Estate, and remains so. It's private property, and although there is a public right to walk across it, visitors need to find somewhere on the main road to park.

We didn't have time to get very good photos, but hopefully this one gives some idea of its rough-hewn, robust magnificence.

As a PS for anyone wondering when this series of posts will actually come to an end, we are getting close. There’s one more bridge from the second day of our trip, and then four bridges from the final day. All five may well be the best from the entire journey.

Further information:

05 September 2012

Kruunusillat contest to restart

After a delay of a year, Helsinki's Kruunusillat bridge design competition is finally to move forward.

Following submission and evaluation of prequalifications, the contest ground to a halt last year when one entrant, Leonhardt, Andrä und Partner, decided to challenge the evaluations in court. Now, the Finnish commercial court has rejected that challenge, and the scheme can again move ahead. No date has yet been set for the restart, nor have the chosen ten competitors been officially announced.

However, I've seen the prequalification evaluation report, and here are the ten teams I expect to be taking part in this competition:
  • WSP Finland / Knight Architects
  • Arup / UNStudio
  • Carlos Fernández Casado
  • Pontek Oy
  • Knippers Helbig / Zwarts and Jansma
  • Apia XXI / Batlle and Roig
  • Schüssler-Plan Ingenieurgesellschaft / Dietmar Feichtinger Architectes
  • Setec TPI / RFR
  • Roughan O'Donovan / Michel Virlogeux / Dumetier Design
  • Arup / Amanda Levete Architects
There are some well-known names in there, as well as several that were previously unknown to me. I would say they are all quite capable of producing a fine design for a 1km long light rail viaduct, which is the central substance of the design competition.

However, there were a number of very big names who failed in prequalifying. As well as Leonhardt, these include the likes of Zaha Hadid Architects, Gehry Partners, Studio Daniel Libeskind, Ramboll, Rosales & Partners, Marc Mimram, Aecom, Flint and Neill, Schlaich Bergermann und Partner, Ney & Partners, Buro Happold, and many more. Several of these are clearly as competent as the firms which did prequalify, if not considerably more so in some cases. It's also clear that this was a very attractive project for some major designers, no doubt helped by the payments available to competitors, which are generous by comparison with many other bridge design competitions.

The evaluation process was based almost entirely on participants' prior experience of projects similar to the Kruunusillat scheme. That would seem to offer little scope for the ambitious and talented, but if a client judges that a safe pair of hands is what's important, then that is their choice.

What was notably more peculiar was their insistence that the projects submitted to demonstrate experience had to be on the personal CV of the lead structural and architectural designers. I find that quite bizarre given the way that most designers operate as teams. Will the success or failure of Kruunusillat's chosen design really depend on the prior experience of figureheads? I find that absurd.

If this were not bad enough, the actual prequalification evaluation process looks quite comical when seen from outside. One of the failed entrants, a structural designer respected worldwide for their landmark bridge expertise, was judged as follows (scoring a miserly 65 marks out of a possible 200 for structural engineering):
"Structural designer who has solved the problems conventionally. The overall structural engineering impression of the references is ordinary. However, the references lack broad projects with overall responsibility for planning."
Two very well-known, very large international consulting engineers, both with an excellent track record in bridge design, secured only 20 marks out of 200 in the same category.

Another entrant, a world-famous architect, scored 80 out of a possible 100 for bridge aesthetics, despite securing these comments:
"Very few bridges or infrastructure projects presented. It is hard to judge if the applicant would have anything to offer in the bridge design even if the building projects are interesting with highly expressive forms. This kind of design approach would probably not suit at all to bridge design where special care has to be given to integrate the structures to the aesthetic design. Moreover the applicant's contrasting attitude to the surroundings in the very valuable competition area probably wouldn't lead up to good results. Why did not the applicant join forces with somebody else having the required bridge references?"
I could easily offer many similar examples here, but you get the point. The evaluation was, at best, highly subjective, and at worst, crassly incompetent. I am sure those taking part will provide some excellent designs, but there is more than one consultant who should feel aggrieved at how the scheme's design procurement has been handled so far.

Leonhardt's submission to the Finnish court raised much the same issues. They contended that the numerical marking and verbal assessment were inconsistent; that the marking for other contestants was so inconsistent as to indicate a lack of objectivity; and that the criterion eventually used for scoring had not been properly set out in advance in the City of Helsinki's invitation to prequalify. The court's decision can be found online.

04 September 2012

Scottish Bridges: 48. Garbh Allt Shiel Bridge

Continuing further westwards, the next span across the River Dee is yet another metal suspension footbridge, to be added to those at Cambus O’May, Polhollick, Abergeldie Castle and Crathie which I’ve already discussed. I don't think there can be another river in Britain with a collection as good over a similar distance.

This bridge provides foot access from the main road, the A93, across the Dee to the private Balmoral Estate. Accordingly, it is a private bridge and we weren’t able to set foot upon it (there’s a locked gate at the north end). As with the bridges at Cambus O'May (1905) and Polhollick (1892), it was built by James Abernethy & Co., in this case in 1924. It goes by many names - in addition to the one I've used, it's also referred to as the Invercauld Suspension Bridge, and as the Ballochbuie Bridge.

It spans 54.6m, and is Listed Category B. Essentially, it's a replica of the Polhollick Bridge built three decades previously, complete with crenellated pylon caps. Unlike its predecessor, the deck is stabilised by lateral stays which tie it back to the river bank.

Further information: