Scottish Bridges: 4. Harthill Footbridge

After seeing three historic bridges in Scotland, it was time to finish off with something much more modern. So modern, in fact, that it hasn't yet reached its first birthday.

I posted about the £5m Harthill Footbridge when it was installed in October 2008. It spans 70m across the M8 Motorway, connecting the eastbound and westbound service stations at Harthill. It was designed by Buro Happold, adopting the same unusual helical form they had previously applied to Edinburgh's Greenside Place footbridge.

At Greenside Place the complex steel truss had (some) justification, as the bridge is S-shaped on plan and the helical truss is to some extent an efficient way of resisting the resulting torsion.

Nonetheless, it's a very expensive solution, as the cost of bending and welding together all the tubular elements must be well in excess of what is involved in a more conventional truss or box-girder solution. It also leads to a substantial amount of understressed metalwork, as the same cross-section appears visually to be applied throughout, although the various load effects in the bridge will vary considerably.

At Harthill Services station, these issues become more prominent, as the bridge is straight in plan and hence torsion is greatly reduced. The bridge's aesthetics also become far more problematic - a bridge looking like a tube can look okay when spanning between the vertical facades of buildings (see also Manchester's Corporation Street footbridge for an example). When sat with its ends in mid-air, it looks awkward.

The end termination problem is exacerbated by the very short cantilever end spans (I believe the spans are 10m, 70m, 10m) and the very differently styled approach ramps, which are there to provide disability access without the maintenance liability required by a lift. Personally, I think lift towers at either end would have looked far better. The new staircases are also somewhat cheap-looking compared to the rest of the bridge.

Of course, many of these issues are likely to be the result of choices outside the designer's control. The approach walkways, staircases and span arrangements will all be constrained both by the limitations of the site and of the client's budget. An attempt has been made to use interesting "trussed" parapets on the approach ramps to echo the diagonals of the main span elevation, but it just begs the question of why the main span isn't also a more straightforward Warren truss. Indeed, why is it covered at all, when there is a lengthy uncovered approach at either end?

The bridge is not without its attractions. The helical truss allows the main structure to be divorced from the glazed walkway enclosure, acting as a skeletal cradle, with an interesting visual rhythm (it will also make the outside of the glass a bugger to access for cleaning). It's also undoubtedly nice to see a major UK highways client investing in something aesthetically different and avoiding the identikit bridges which litter British motorways.

But for me, this was an interesting bridge to stop and see, but not one to love.

Further information:

• Location on Google Maps
• Page at Structurae
• Scotmans article about delays and costs
• Video at BBC Scotland
• Project website at Transport Scotland

Scottish Bridges: 3. Rumbling Bridge

Rumbling Bridge. It was just a dot on a map, but with a name like that it was a dot that just begged for a visit, especially after seeing two Shakking Bridges already on my trip to Scotland.

According to the internet, which is supposedly never wrong, the original Rumbling Bridge was built in 1713 by William Gray, carrying a road across the River Devon, at a point where it drops deep into a gorge, the water's rumbling sound giving the bridge its name. It's a masonry arch spanning about 7m, and without any parapets.

Again according to the internet, the second arch bridge was built above the original in 1816, leading to an unusual double arch bridge which is well worth seeing, particularly above the somewhat spectacular river gorge.

Quite how accurate or complete the internet's information is must be open to doubt, as there's a stone clearly visible on the bridge inscribed with the name "T.H. Tuckett" and dated 1664, which suggests there was a bridge on this site at an earlier date.

The photo at the start of this post is a panorama and hence slightly distorted and doesn't really give a good idea of the depth from the top of the bridge to the river below - it's deeper than it looks (36m). The old postcard on the left gives a slightly better idea and shows that at one time it was possible to walk across the lower arch - it's a real shame that's no longer an option.

It's unclear precisely why the lower arch bridge was left in place, as it must have been rendered largely unuseable during erection of the timber centering for the upper arch, and remains unuseable now. I did wonder briefly whether it formed some propping function, but that also seems unlikely.

Whatever, it's an unusual and picturesque bridge, worth the short detour from our journey.

Further information:

• Page on Wikipedia
• Location on Google maps

Scottish Bridges: 2. The Shakkin' Brig

No that's not a typo, fresh from my visit to Aberdeen's Shakkin' Briggie, it was time to visit Edzell's similarly monickered Shakkin' Brig. Like the bridge over the River Dee, the Edzell bridge is a suspension footbridge, although it's not yet a ruin, and not particularly shaky, either.

It was apparently built in 1900, although I think little of the current structure is that old, and I gather that it was rebuilt in the mid-1990s by US servicemen. It crosses the North Esk river just east of the town, and can be found from a footpath behind the village post office.

Quite how much it has been altered is hard to identify: the image above right is from the 1970s (courtesy of RCAHMS), and it doesn't seem much different today. However, old postcards like the one on the left (date unknown) seem to show very different towers to those now present.

Structurally, it's Edzell's little equivalent of the Brooklyn Bridge, with a hybrid suspension and cable-stayed support system. You can just about make out the cable-stays on the image on the right. You can also see horizontal tie rods, which run from the midspan diagonally to the bank, and ensure that the Brig is not really very Shakky.

The tower-tops support a mess of cable rods heading off in what seems like several arbitrary directions. The anchorages are similarly higgledy-piggledy in their layout.

What I like about the Edzell bridge is the detailing. Like many rural bridges, the simple mesh parapets and chicken-wire anti-slip tread (shown right) are a cheap but effective solution which (sadly) slavish adherence to design standards rarely allows to spread more widely.

The eyelet connection between the hangers and the main cable chains, shown on the left, is similarly delightful in its simplicity (if clearly unsuitable for any more significant bridge).

The Shakkin' Brig at Edzell isn't a startling design, nor an especially historically significant structure. Its lack of Shakkiness is really rather disappointing.

But it's a fine example of robust vernacular construction (it would seem almost a shame to query who the designer was). It's also a good example of the continuing relevance of the suspension bridge form to relatively tiny spans (for other examples of similar historical vintage see the bridges of Louis Harper or David Rowell).

Further information

• Location on Google maps

Update 1 May 2009:

I'm told by ex-US Navy Seabee Robert Deese that the bridge was rebuilt in the mid-90s, by a four-man team, essentially replacing all the timber (which was rotten) with new pressure and chemically treated wood. So, the current design dates at least from before then. According to Robert:

"The rebuild was requested by the village because the bridge was unsafe. We supplied the labor at no charge and the village paid for the materials. The job was completed in 4 weeks right in the middle of winter. I had to take a swim twice to recover tools that dropped in the river. Man was that water cold!"

Scottish Bridges: 1. The Shakkin' Briggie

I recently made a trip up and down the east coast of Scotland, and while looking for bridges was far from the purpose of the journey, I did visit one or two along the way.

These weren't necessarily spectacular structures in any way, indeed several were in varying states of dilapidation ranging from "senior citizen" to "six feet under". But they all had enough of interest to merit including them here.

The first bridge of interest was Aberdeen's Shakkin' Briggie, also called St Devenick's or Morison's Bridge. Built in 1837 on behalf of a local churchman, the bridge was designed by Aberdeen's city architect John Smith, who had worked six years previously with Captain Samuel Brown to design the Wellington Suspension Bridge, also in Aberdeen. The image on the right (courtesy of RCAHMS and dating from the mid-1970s; all B&W images are from the same source; all colour images are mine) shows the bridge a few decades ago and gives a fair idea of its original appearance.

The 55m span suspension footbridge originally provided access across the River Dee for over 700 churchgoers, and got its nickname from its somewhat flexible unstiffened deck.

The bridge was damaged several times by flooding, and affected by changes in the river channel, with its southern spans destroyed in 1955. In 1971, it was declared a Listed Building, but this offered it little protection as in 1984 it had deteriorated so badly that all the decking was removed. The image below right is from the mid-70s while it was in poor condition but still largely intact.

Its twin problems were that nobody knew who actually owned it, and that it was no longer part of a significant footpath route.


Today, it's a sad sight. As is often the case with historic bridges, it has been allowed to fall into ruin over the years to the extent that is probably now beyond repair.

Its Doric-style cast iron columns are heavily rust spotted, while the iron bar main cables and hangers are sufficiently rusty that it's surprising they haven't fallen into the river. Transoms connecting the hangers might suggest an unusual way across for an enterprising trapeze artist, at best.

There seems no hope of resuscitation from its current comatose state, but this elderly patient still endures. It sits silently, an accusation against municipal penny-pinching and lack of foresight. At any point, it could have been saved for the cost of medicinal repair far less than would now be required to give it renewed life.

If this were a ruined stately home, it would be given protection and funding by a body like Historic Scotland. Its Listed status might actually offer it some assistance. But the vision needed to create new riverside paths that might justify funding for refurbishment seems to have remained absent for a quarter of a century now.

It's hard not to assume that within the next quarter century, much of what now remains will end up at the bottom of the river.

Further information:

• Location on Google maps
• Page at Bridgemeister
• Page at Wikipedia
• Page at Royal Commission on the Ancient and Historical Monuments of Scotland (lots of historical images and drawings of the bridge)
• Aberdeen City Council report on possible restoration [PDF]
• Scotsman article on possible restoration

Bridges news roundup

Not much happening at Happy Pontist Towers right now ... I've a review of Peter Bishop's book "Bridge" in the offing, and another handful of bridge competition debris posts planned. Hopefully in the near future the losing entries to the Leicester River Soar and Dublin River Liffey bridge design competitions will be made public. There should also be announcements made of the winners in design contests in Rhyl and Worcester any day now.

Is there bridge news you think I should be covering? If so, post in the comments here.

Meanwhile, here's a quick news roundup to keep things ticking over ...

Naeem Hussain interviewed on Third Forth Crossing
Great to see a bridge engineer the focus of attention

Civic Trust Award for Castleford Footbridge
Partnership award for S-shaped structure

Supplied Clyde Arc hanger forks met specification
Claims Macalloy

Hakes bridge design takes it to Moscow
Pontist notes cat's cradle design to be inefficient but couldn't summon energy to comment further

Bridge competition debris part 12: River Wear

The River Wear Crossing bridge design competition will need little introduction to regular readers: I've covered the outcome extensively on several occasions here.

Organised by RIBA on behalf of the regeneration company, Sunderland Arc, the competition sought a design for a highway bridge across the River Wear, with the organisers being quite explicit that they were looking for something iconic. The winning design (pictured right), by Techniker and Spence Associates, is currently undergoing further technical development before Sunderland City Council decide whether or not they can afford it.

I've been keen for some time to publish the other entries, the five designs that weren't chosen. H0w is the winner to be properly judged if not against its peers? Sadly, Sunderland have refused to release images of the other entries, and my enquiries with the designers have, with the two exceptions shown below, drawn a blank.

Three losing entries came from Halcrow, Flint and Neill, and Dissing + Weitling; Hyder and Yee Associates; and Jacobs Babtie, Leonhardt Andrae und Partner, and Marks Barfield. I would love to show you these, so if any of the designers would like to send through their images, please email happypontist at googlemail dot com.

The other two losing entries are shown below courtesy of Schlaich Bergermann, and Wilkinson Eyre. How do they compare against the winner?

In many ways, all the designs share a desire to adopt an unnecessary and inefficient structural form purely to shout "look at me". That's not unreasonable - I think it's a large part of what Sunderland were looking for.

The Gifford / Wilkinson Eyre design is far more economic than the winning entry, with a cable layout that doesn't impose too many unnecessary forces on the support tower, particularly in the way the cables are arranged in plane with the axis of the V-shaped pylon arms (minimising bending moments).

That V-shaped pylon itself, of course, runs the risk of being seen in Sunderland as a two-fingered salute to local rivals such as Newcastle - see, our bridge is bigger, better. I can't help thinking the basic geometric idea (the X-shaped pylon and cable arrangement) doesn't quite make sense here, but could be developed into something interesting on a different site.

The images of the Schlaich Bergermann entry are a real curiosity, as much for the insight into their creative process as for the unlikely solution itself, a combination asymmetric cable-stayed suspension bridge, from which giant glass scales are suspended. Gehry doesn't strike me as an architect with much sympathy for the normal imperatives of bridge design - his work is about shape and surface rather than structure, and his non-linear, protean forms are at odds with the linear, refined forms normally suited to bridges. Jörg Schlaich, on the other hand, is a giant of engineering notable for pushing the boundaries of structural innovation without normally departing from the primacy of his structural ideas.

The Gehry / Schlaich design for River Wear seems to have its origins in Schlaich's 1989 Neckarstrasse footbridge, albeit at a larger scale and with the reverse suspension cable (the one that curves out of the tower like a letter D) much improved in shape. The only similar design I can recall seeing is Robert Benaim and Powell Williams's design for the Royal Victoria Dock bridge. Like that bridge, my first thought is about the difficulty of cable replacement once in operation.

Gehry's glass scales simply aren't my cup of tea, they seem like an afterthought, and I can easily imagine the judging panel worrying about both how they'd be restrained, maintained, and protected against damage. I do, however, admire the way that Gehry brought something so unpredictable to the design.

So, if you had to choose between these three designs, which would you choose, sat in Sunderland's shoes?

As with all these posts, click on an image for a full-size version.

Gifford / Wilkinson Eyre


Schlaich Bergermann / Atkins / Gehry Partners

Squiggly bridge unveiled

The Broomielaw-Tradeston Footbridge has been unveiled in Glasgow, with the shrouds which were present (pictured below left) while it was welded and painted removed last week (pictured right). It won't actually open to the public until May, but the video at STV's website gives some idea of what to expect.

The design, by Halcrow and Dissing + Weitling, won a design-and-build competition in the aftermath of the failed "glasgowbridge" competition. It was far less ambitious than the entries to the original competition, representing a much more sober, risk-averse approach to the crossing.

In the time of the credit crunch, the bridge looks somewhat forlorn (an impression enhanced by STV's melancholy video soundtrack). There was always doubt about whether this bridge actually led anywhere (in theory, it's to help regenerate the south bank of the River Clyde, but until the regeneration happens there's little to go and see). However, until the wider economy recovers, it's likely to look like something of a white elephant. Unlucky timing for a bridge meant to provide the area with a sense of excitement.

The lack of colour, and the pristine joint-free surfaces to the steelwork (see picture, right), give an air of artifice rather than robustness - to the layperson, the bridge might just as well be made of plastic, with so little evidence of its making. The arrow-head towers are basically cable-stay bridge towers, with the stays replaced by box girders in order to provide sufficient restraint to an ultra-thin deck that is curved (hence "Squiggly") in plan.

The geometry of the various arrowhead surfaces seems designed to bring it to a point at its tip, while keeping steelwork in simple planes for ease of fabrication. But the effect looks a little odd, especially on the shaft of the arrow, where the box member walls taper in different directions. I find the connection of the "stays" to the deck a little peculiar too, likewise the way in which the arrowheads offer only a very limited visual response to the curvature of the deck (compare for example the more dynamic pylons on the South Quay Footbridge in London, especially in its original full S-shaped configuration).

The use of box-girder stays instead of cables might present a tempting target to Glasgow's skaters, climbers, and drunks. I'm not sure whether the curved notch at the base of the "stays" (pictured left) is intended to try and reduce this, but it will be interesting to see how well it works in practice.

I admire the minimalist simplicity of the design, while longing for the far greater sense of occasion that the original competition entries generally offered. Only time will tell what the Glasgwegians think of it.