Scottish Bridges: 53. Loups Bridge

Loups Bridge is another of John Justice Jr's structures. We'd been to his other bridges at Crathie, Kirkton of Glenisla, and Haugh of Drimmie, and Loups Bridge completes the set: the only other Justice bridge known to survive.

Loups Bridge spans the River North Esk not far from Edzell. I guess it is named for the waterfall which cuts through a rocky channel just below it, "loups" referring to a salmon leap.

The bridge is on private land, and I'm not clear whether normal Scottish rights of access to walk across the land apply, as it is in the grounds of a partially residential building. The Happy Pontist had obtained permission from the landowner to visit the bridge on this occasion.

The bridge has two spans, supported by a masonry pier at its centre. The RCAHMS website lists the spans as 9m and 10m, but also states 15m and 17.4m, while Ruddock's paper lists two equal 36 foot spans. I don't know which is right.

The bridge is Listed Grade B, and seems of considerable historic importance as a rare example of the Justice family's work, and also as one of the earliest surviving stayed bridges in the UK. Its exact date of construction is unknown. It may possibly pre-date the stayed footbridge at Kirkton of Glenisla, which was built in 1824, or the Haugh of Drimmie bridge from 1823.

Unlike the other Justice bridges that we visited, Loups Bridge is derelict. Very little of it remains, and it would be foolhardy to try and walk across it. It is more than a ghost of a bridge, but only barely so.

From what can be seen, it's clear that the bridge's skeleton must have been exceptionally slender even by the standards of other Justice spans. The stay rods and cross-members are tiny in cross-section, and the odd arched pylons above the pier are not made out of anything more substantial. There are two wire-like stringers which must once have been below a timber deck, and I would guess there were once longitudinal edge members providing tension ties to the inclined stays. Most of what now remains would once have formed the wire-fence balustrades.

It would make for a very interesting restoration project, but I suspect this bridge is well past the point where it can be repaired.

Further information:

• Google maps / Bing maps
• RCAHMS
• British Listed Buildings
• Aberdeenshire SMR
• Some iron suspension bridges in Scotland 1816-1834 and their origins (Ruddock, The Structural Engineer, 2003)

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:

• Google maps / Bing maps
• RCAHMS
• Engineering Timelines
• British Listed Buildings
• New Statistical Account of Scotland, Vol. 10 (1837)
• Scottish Suspension Bridges (Hume, Scottish Archaeological Forum Vol. 7, 1977)
• The 19th century iron bridges of Northeast Scotland (Day, Journal of the Society for Industrial Archaeology, 1998)
• Some iron suspension bridges in Scotland 1816-1834 and their origins (Ruddock, The Structural Engineer, 2003)

Updated 27 September 2012:

See the comments on this post for some very interesting additional information about this bridge.

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:

• Google maps / Bing maps
• RCAHMS
• British Listed Building
• Angus SMR
• Scottish Suspension Bridges (Hume, Scottish Archaeological Forum Vol. 7, 1977)
• The 19th century iron bridges of Northeast Scotland (Day, Journal of the Society for Industrial Archaeology, 1998)
• Some iron suspension bridges in Scotland 1816-1834 and their origins (Ruddock, The Structural Engineer, 2003)
• Civil Engineering Heritage - Scotland Highlands and Islands (Paxton and Shipway, 2007)

Scottish Bridges: 46. Crathie Suspension Bridge (revisited)

Continuing west (and upstream) along the River Dee, the next bridge is the Crathie Suspension Bridge. This was one of the bridges I was most keen to see on this Scottish bridge tour. I had been to it previously many years ago, but before I was aware of its significance, and I also failed to take very good photographs.

It's such an interesting and significant bridge, that I'll repeat some of what I said last time I featured the bridge here.

The bridge spans 42m, and it is 4.3m wide. It was built in 1834 to carry carriages, although it is now only open to foot traffic. It was designed and built by John Justice Jr, one of a family of blacksmiths from Dundee. Five bridges are known to have been built by Justice, of which only three survive intact, with one derelict, and one, at Glen Clova, now gone.

In his paper on early Scottish suspension bridges, Ted Ruddock described the structures as "vernacular bridges", which hits precisely upon what interests me about them - the ingenuity and eccentricity of bridges designed by direct experimentation rather than from the custom and habit which hamstrings many professional bridge designers.

We were lucky enough to visit all four surviving Justice bridges on our trip, and they certainly are marvels.

The bridge at Crathie appears to have been originally built as a "cable-stayed" structure, although it was refurbished in the mid-1880s by Blaikie Bros (the firm also responsible for the bridge at Abergeldie Castle). It's believed that was when the suspension chains were added.

Along with its siblings, Crathie is one of the earliest stayed bridges to survive in the UK, and possibly in the world. It's incredible that it has lasted so well, as many early stayed designs were conspicuous failures, accounting for the form's widespread unpopularity before the mid-20th century.

At first sight, a number of features of the Crathie bridge suggest that it might have been the work of “proper” engineers. The A-frame towers have clean, strong lines not entirely unlike the suspension footbridges of the later 19^th and early 20^th centuries.

However, the closer you look, the more features appear that indicate a more idiosyncratic hand at work. The layout of the rod stays is one, as is the way in which the rods are connected together, with open-form “turnbuckle” connectors. The stays in the main span form a double-fan arrangement, with two stays coming together at each of two points on the towers.

From each point on the tower, only a single, larger stay continues on to the bridge anchorage. At the south end, even these two anchor stays connect together at a fork before a single rod is anchored.

Perhaps the oddest feature of the stay rods is that the part of the stays which passes through the towers is curved, with the curves extending beyond their points of support. Where ties are continuously curved over their support, you would expect them to sit on a curved saddle to eliminate bending in the rod. As it is, the rods are subject to considerable bending at their upper end, which must hugely reduce their effectiveness. What's even stranger is that the same arrangement has been replicated in the later suspension chain supports.

The suspension chains added during the bridge’s refurbishment are of very different form to the main stays, consisting of flat wrought iron links held together with pins in a manner not dissimilar to many other 19^th century suspension bridges. It’s impossible to guess to what extent the two structural systems contribute to the bridge’s ability to bear loads – the stays are stiffer, but imperfectly engineered.

Both systems are abetted by further structural elements which can only be seen from the riverbank. These consist of small bowstring trusses spanning transversely, as well as larger ones spanning longitudinally. Despite their lack of triangulation, these must provide vital stiffness to the structure.

From below, you can also see lateral ties which run diagonally from the deck back to the abutments, on its west side (the right-hand side in the photo). I guess there may once also have been ties on the east side. In any event, the remaining ties are now loose and no longer helping to stabilise the bridge.

The profusion of structural rods, bars, and struts is not especially aesthetically pleasing, although I quite like its unembarrassed pragmatism. However, what I admire even more is the exceptional slenderness of all the various bridge components. With the exception of the tower legs, there are no metal parts more than an inch or two thick anywhere on the bridge. It seemed largely immune to wobble when we crossed it. Aside from cable-net structures, it’s hard to think of a contemporary footbridge equivalent, which suggests that modern designers may still have more to learn from the past.

Further information:

• Google maps / Bing maps
• British Listed Buildings
• Scotland's Places
• RCAHMS
• Scottish Highland Bridges
• Aberdeenshire SMR
• Engineering Timelines
• Bridgemeister
• Scottish Suspension Bridges (Hume, Scottish Archaeological Forum Vol. 7, 1977)
• Highland Bridges (Nelson, 1990)
• The 19th century iron bridges of Northeast Scotland (Day, Journal of the Society for Industrial Archaeology, 1998)
• Some iron suspension bridges in Scotland 1816-1834 and their origins (Ruddock, The Structural Engineer, 2003)
• Civil Engineering Heritage: Scotland Highlands and Islands (Paxton and Shipway, 2007)
• An Encyclopaedia of Britain's Bridges (McFetrich, 2010)

Scottish Bridges: 18. Crathie Suspension Bridge

As with the Craigmin Bridge, I don't have any really good photos of the suspension footbridge at Crathie.

This bridge spans the River Dee in Aberdeenshire, just outside the grounds of Balmoral Castle. It was originally built in 1834 to carry carriages, to a design by John Justice Jr, although today it is open only to pedestrians. A wrought iron girder road bridge to Balmoral was built nearby in 1858 to a design by I.K. Brunel.

Justice was a highly innovative engineer, experimenting with variations on rod-stayed and suspension bridge form. His bridge at Haughs of Drimmie, Perthshire, combined a rod-stayed system with an under-deck suspension truss, while the earlier (and charmingly primitive) 1824 span at Kirkton of Glenisla, Angus, combined rod stays with shallow suspension bars incorporated into the parapets. Both are probably unique in their form, and it's amazing that they have survived to the present day.

As originally built, the Crathie bridge was very similar to the Haughs of Drimmie design, consisting of rod-stays supplemented by lightweight under-deck trusses. It seems I didn't take any photos which actually show the bridge in elevation, so you'll have to visit one of the links at the end of the post to understand what happens below the deck.

Although originally built as a "cable-stayed" design, the bridge was "renewed" in 1885 by Blaikie Bros., which is presumably when the iron flat link suspension chains were added.

Crathie Suspension Bridge is featured in several books, but astonishingly, Justice's other bridges are less well recognised. The Haughs of Drimmie bridge isn't even in Civil Engineering Heritage: Scotland, and none of these bridges are recognised in Walther's or Troitsky's books on cable-stayed bridges. It makes you wonder how many other remarkable bridges have escaped the attention of the historians.

With the other Justice Jr bridges, this is one of the earliest "cable-stayed" bridges built in the UK which still survives, although not the earliest unaltered example (that will be a story for another day).

Further information:

• Google maps / Bing maps
• British Listed Buildings
• Scotland's Places
• RCAHMS
• Engineering Timelines
• Bridgemeister
• Civil Engineering Heritage: Scotland Highlands and Islands (Paxton and Shipway, 2007)
• Highland Bridges (Nelson, 1990)
• An Encyclopaedia of Britain's Bridges (McFetrich, 2010)
• Scottish Suspension Bridges (Hume, in The Archaeology of Industrial Scotland, 1977)
• The 19th century iron bridges of Northeast Scotland (Day, Journal of the Society for Industrial Archaeology, 1998)
• Some iron suspension bridges in Scotland 1816-1834 and their origins (Ruddock, The Structural Engineer, 2003)