09 December 2013

Bridges news roundup

Here are a few news links that you have probably already seen. I'm travelling over the Christmas period, so it will probably be January when I finish off my reports on the IABSE study tour of north-east England.

New Thames footbridge gets planning
I really dislike this so-called Golden Jubilee bridge, which is proposed to cross the Thames between Battersea and Chelsea Harbour in London. The proposed span arrangement, with a short middle span flanked by two larger spans, with correspondingly larger support arches, just seems to have a really awkward rhythm to it. Although the bridge has now won planning consent, it still appears to have no funding. Incidentally, if you don't have a BDonline subscription, you can read their news stories by simply copying-and-pasting their headline into Google, then following the link from there: this bypasses the subscription protection.

£60m boost for Thomas Heatherwick's garden bridge
The Golden Jubilee Bridge is a ridiculous enough proposal, but the Garden Bridge is an absolute disgrace, an absolute eyesore where money is no object if it serves to boost the vanity of all involved. The total project budget is £150m, which is absurd for a bridge which is so utterly unnecessary.

Striking but useless… just like Boris
It seems I am not alone in this opinion. "It has just the right combination of whimsicality and instant-wow theme-park tackiness to make it a likely Boris project."

Shortlist announced for Hisingsbron in Gothenburg
So far as I can tell using Google Translate, five proposals out of 24 submissions have been shortlisted in this competition to design a new moveable bridge. The finalists are Snøhetta / WSP, Zaha Hadid, Tyréns / Beam / Schlaich Bergermann, Dissing + Weitling / Lenonhardt Andrä, and Wilkinson Eyre / Ramboll. That's a mighty impressive roll call of bridge architecture names, along with one or two less so. All five shortlisted entries are available online, where you can play guess-the-architect. All I can say is that three out of the five submissions are quite horrible, and you really have to wonder what the participants were thinking.

Beautiful bridge planned for China's Hunan province evokes knots, Möbius strips
This depressingly awful bridge proposal has been all over the architecture blogs, but few have managed such an inappropriate title. Beautiful? In the eye of the beholder, perhaps. If they are blind.

I told you so, St. Patrick’s Island Bridge
Following flood damage during construction earlier this year, parts of the RFR / Halsall designed footbridge had to be disassembled, setting back the date for the bridge's opening. Tallbridgeguy takes the opportunity to say "I told you so".
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04 December 2013

Shortlist published for Salford Meadows bridge competition

The four shortlisted entries to the RIBA Salford Meadows footbridge design competition have been made available online, and also as part of a public exhibition. Comments are invited from the public, with an online deadline of 6th December.

I previously showed some of the shortlisted entries here, as well as a selection of the many unsuccessful entries. I gave some more detailed comments on the contest back in June.

I'm a bit pushed for time right now, but if I get a moment, I'll post some more images and thoughts here.
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02 December 2013

Durham Bridges: 3. Framwellgate Bridge


Framwellgate Bridge pre-dates the nearby Prebends Bridge in Durham, but is a significantly more attractive and impressive structure.

A bridge was built at this site in the early 12th century, by Bishop Ralph Flambard. It was protected by a gateway and tower, until destroyed in a flood in 1400. The replacement bridge consisted of two segmental arched river spans, and one much shorter land span. The land span is no longer visible, although it may be hidden by later buildings. It can be seen on a painting by Thomas Girtin, and if it does still exist, it may be a survivor from the original bridge.

The river spans are ribbed arches, originally with five ribs, and later widened to seven. As with its predecessor, it was originally protected by a gatehouse, removed in 1760 because they hindered traffic.

The shallow spans are very attractively proportioned. They are separated by triangular breakwaters. I think the slight recessing of the arch facing stones is a large part of the attraction, and spandrel tie bars have been added in a way which complements rather than detracts from the bridge's appeal.

This was pretty much the last bridge we visited on the first day of our IABSE study tour. We did visit the Gateshead Millennium Bridge in te evening, but I'll cover that when I run through all the Tyneside bridges that we visted on our second day.

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01 December 2013

Durham Bridges: 2. Prebends Bridge

The centre of Durham is dominated by a large loop in the River Wear, which passes around the peninsula on which sit both Durham Castle and Durham Cathedral. While this may have been a highly defensible site when the Castle was built in the 11th Century, it must have proven an increasing constraint on travel as the centuries wore on.


Prebends Bridge was one of three mediaeval bridges to be built which spanned the river. Originally, it was the site of a ferry. In 1574, this was replaced by a timber bridge built on stone piers, although that was swept away in the floods of 1771. The present bridge was completed in 1778, funded by the Cathedral and designed by George Nicholson.

The bridge has three semicircular stone arches. The parapet is generally solid, but opened with balustrades near the crown of each arch. There are triangular cutwaters, with a semi-hexagonal geometry above the base. The face of the arch ring is "dentilated", and you can see waterspouts on the elevations which assist with drainage.

These are an unusual feature. Poor drainage is a common feature in old masonry bridges, but the details of this bridge seem better thought out than most. Viewed from above, you can see a succession of scalloped humps in the road, assisting water in draining towards the waterspouts. I can't remember seeing this feature anywhere else.

Despite this, the bridge has suffered from masonry deterioration, and it was closed to traffic entirely in 2011.

It's not the prettiest of Durham's bridges. The regular procession of arches seems stilted, and I think it would have looked better if the open balustrading was continued over more of its length. I imagine it looks much more attractive on a calm and sunny day, when it reflects better in the water.

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28 November 2013

Durham Bridges: 1. Kingsgate Bridge

The last few posts dealt with bridges on Teesside that I visited as part of an IABSE study tour. On the afternoon of the first day, we travelled a little further north, to Durham. Our first stop: Kingsgate Bridge.


Built in 1963, this footbridge was personally designed by Ove Arup, and is reported to have been one of his favourite designs. At the time, Arup was probably more involved in running his Partnership than in the specifics of individual projects, but for the Kingsgate Bridge he immersed himself in every detail.

Famously, the University in Durham had only £35,000 to spend on a new bridge linking their older buildings by Durham Cathedral to a new site on the opposite bank of the River Wear. They anticipated this would be enough only for a bridge at the river valley floor, some 17m below the tops of the valley slopes. Arup convinced them that the same money could pay for a 107m long bridge running at height, if the structure could be made efficient.

The engineering of the bridge displays a masterful balance of structural requirements with construction requirements. The bridge has only two main support points, each on a piled base. From these, V-shaped "fingers" carry the bridge deck, reducing the deck spans. The arrangement also allowed for a highly economic method of construction, eliminating the need to construct reinforced concrete in-situ above the river. Each half of the bridge was built parallel to its river bank. The pier supports conceal an internal cone, which allowed both 150-ton halves of the bridge to be rotated 90 degrees into their final position.

This is certainly not a unique construction method, but it is relatively rare and I'm not sure whether there were any precursors in the UK at this time.

At first sight, the bridge is not an immediately loveable design, notwithstanding its status as a Grade I Listed Building. The supports are stiff and angular, and the bridge deck, apparently envisaged as a "thin, taut, white band stretching horizontally across the valley", is blank and lumpen. As the river banks have become considerably overgrown, it's also almost impossible to see the entire bridge as the single composition which was originally built.

Even in detail, the bridge has its flaws, and I find the "fingertips" which connect the finger piers to the deck to be particularly awkward. There's little sense of how the forces are transmitted (the deck is in tension between the fingers, and that considerable force has to be transmitted through these tiny fingertips). There's no shaping of the concrete to respond to those forces either: the band-like concrete side-beams are the same depth at the ends as at the middle, although the stresses in each section are very different. Arup was certainly not a master of concrete on the level of Maillart, Torroja, Candela or their ilk.

Nonetheless, it's an admirable bridge in many ways. The detailing of the finger piers is interesting, minimising material while providing stiffness by means of a folded cross-section that constantly transforms from top to bottom. And the bronze expansion joints where the two bridge halves connect are quite exquisite. These allow horizontal movement while locking the bridge decks together vertically.

I am not generally a fan of "half-through" footbridges, where solid beams on either side of the walkway double as the parapets. Generally, visual transparency seems preferable. However, for a footbridge at height, as is the case here, solid parapets do offer a much greater sense of security for the bridge users.

Shortly after the bridge was built, Concrete Quarterly praised it for having a "subtlety without chi-chi or softness, but keeping in its fineness a certain strength of plane". Its angularity closely recalls the great Italian engineer Riccardo Morandi, whose structures are equally hard to love. Today, I think it would be improved considerably simply by cutting down a few trees and giving it the chance to be seen properly as a sculptural object within the landscape.

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20 November 2013

Teesside Bridges: 4. Infinity Bridge

Okay, it’s white elephant time.


A design competition was launched in 2003 for a new footbridge across the River Tees at Stockton. The intention, as in so many instances, was to use a landmark structure to signpost the local authority’s commitment to developing a new area, on the north bank of the Tees, and attract in outside investment. A budget for the bridge of £4.5m was stated.

The competition was won by Stephen Spence Associates with Expedition Engineering, who developed the concept for a twin arch bridge, with one arch twice the span of its neighbour. The asymmetric arrangement kept the central part of the river free from obstacles, this part of the river being used regularly for rowing training. There was to be some controversy over authorship of the design.

The bridge was completed in 2009, at a cost of £15m, an enormous increase over the original budget, and one which presumably involved the promoter having to plunge their hands deep into their pockets. This is above average for a landmark bridge, but not unreasonably so given the spans involved. The original budget was never enough for a truly iconic structure, and the Infinity Bridge is certainly that.

Visiting four years later, all that our tour group could find on the north bank was mud and grass – none of the hoped-for development has materialised, perhaps unsurprisingly given events in the wider economy. It’s in this sense that the bridge is a white elephant, and it remains to be seen whether the money was well spent.

Nonetheless, the bridge is both spectacular and elegant, and its architectural impact is largely a consequence of engineering requirements rather than the driver for the design. The “reflex curve”, or sag arch, which links the two main arches, originates as a gesture on a sketch. Expedition can make the claim that it is a functional element, as it serves to transfer bending between the two arch ribs, making them both much stiffer and improving behaviour overall. This is, however, probably rationalisation after the fact, a happy but not inevitable outcome.

Several things strike me about the structure. The deck is quite exceptionally slender, comprising a series of precast concrete slabs, prestressed together by the action of the arch’s horizontal bowstring cables.

There is very little stiffness in the deck, and although probably heavy enough to be difficult to excite, it still requires the presence of five enormous tuned mass dampers tucked below its soffit to ensure that vibrations are acceptable. The dampers are impressive but slightly odd – one above the south bank is set horizontally at a location where the deck has a longitudinal gradient, making it look as if the damper is peeling off the soffit and ready to fall.

The arch is tall yet narrow. Most designers, I think, would have adopted a wider arch to provide greater transverse stability. This narrowness is enhanced by the tripod form of each arch, where it bifurcates into two ribs at the central support, but comes to a single rib at the end support. The central support is therefore required to provide all the resistance to wind or eccentric loading. The effect is visually striking, but as an engineer I also found it a little disconcerting. It also means that the deck has to incorporate significant transfer elements to brace between the end supports of the arch (with an outward thrust) and the tie cables along the deck edges (with their inward tension).

The arches are formed from painted structural steel box sections, and generally are shaped attractively. In elevation, their shape was determined by form-finding, to minimise bending moments under dead load. However, the bracing between the twin arch ribs near the main support, which include huge circular sections resembling offcuts from a pipe factory, is much less attractive.


There’s also an odd disjuncture between the plain, minimal profile of the arch ribs, and the centre-pier struts which support them. Both above and below deck, these struts have a “fluted” form, which contrasts markedly with the arch ribs. I don’t particularly like the shape of these elements, although I do think that the high contrast was the visually appropriate decision. It is the shape of the arches including the reflex curve which needs to be highlighted and given visual continuity, even if this is structurally dishonest, in the sense that the primary flow of forces is from the arch rib down towards the point of support. I think this is therefore an instance where the popular maxim that form follows function would have it wrong.

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17 November 2013

Teesside Bridges: 3. A19 Tees Viaduct

By the time the Tees Viaduct opened in 1975, its older siblings (the Middlesbrough Transporter Bridge and the Newport Lift Bridge) must have been a major cause of traffic delays. It's no surprise that a fixed rather than opening bridge was built, necessitating a long, high-level structure. However, shipping on the Tees was already declining, and fifteen years after the viaduct was built, there would be no need for shipping clearance at all, with the Tees Barrage under construction and the Lift Bridge locked down.


The Tees Viaduct was a relatively unremarkable structure, comprising welded steel girders, a composite concrete deck slab, and reinforced concrete piers. The 117m main span contains a central section suspended on half-joints, which was typical of the time although would almost never be adopted today. The bridge totals 1.95km in length, of which 625m consists of fabricated plate girders, and the remainder is built from off-the-shelf Universal Beams.

Designed by Dobbie Sandford Fawcett and Partners, and built by Cementation Construction, the bridge would have been unremarkable if only it had performed well. However, the bridge performed badly almost from the date it was completed. The deck expansion joints leaked from an early stage, the bridge's roller bearings were not operating correctly, and cracking was observed in the concrete piers. These, and many other problems, led to the bridge undergoing major refurbishment just twelve years after it first opened, with the bulk of the work taking place between 1987 and 1990.

 
The leaking deck joints led to road salts contaminating the concrete bridge piers. These were the subject of a number of chloride extraction trials. The roller bearings were replaced, expansion joints renewed, and large areas of deck concrete, affected by faulty waterproofing, had to be repaired. A report in 1999 suggested that the original bridge construction cost had been £10m, but the cost of repairs totalled £25m.

The principal feature of interest on the bridge today, and probably a significant part of that refurbishment cost, is the presence of a glass-reinforced plastic enclosure which surrounds the main girders. This comprises Maunsell's patented "Advanced Composite Construction System", ACCS, later given the name "Caretaker". At the time it was installed on the A19 Tees Viaduct, it was being heavily promoted both as a way of protecting bridges against weathering and corrosion, and also of providing improved maintenance access, particularly at locations where such access might otherwise be difficult. The A19 viaduct crosses both a major river and also railway lines.

 
The only other major use of the system that I can think of, on approach roads to the Second Severn Crossing, had a similar motivation, but bridge enclosures have not proven popular.

The appearance is not as bad as I had though it might be, and the GRP panels seem to be durable so far. It doesn't look significantly worse than an unadorned plate girder bridge. I'm only guessing, but I presume the cost has been the major disincentive to wider adoption. I also wonder whether the system would have had more use if it wasn't shielded by patent.

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14 November 2013

Teesside Bridges: 2. Newport Lift Bridge


Like its neighbouring transporter bridge, the Tees Newport Lift Bridge is both an industrial relic and an icon for the area. The Transporter Bridge had been opened in 1911, and as with all bridges of its type it gave priority to shipping - in its "rest" state vessels can pass but vehicles cannot, and when in motion only a very limited number of vehicles can be carried at one time in one direction.

The lift bridge offered a considerable improvement for road users, giving priority to them insofar as traffic could cross while the bridge was at rest. It opened in 1934, built by Dorman Long to a design by Mott, Hay and Anderson, becoming at that time the first significant vertical lift bridge in Britain, and one of the largest in the world (at 82m, its main span was some way longer, for example, than Rotterdam's De Hef, built in 1927 and spanning 52m, which I also visited recently).

As traffic grew, even less frequent lifts of the bridge could lead to considerable disruption. The bridge lifted for the last time on 18 November 1990, remaining in its "down" position ever since.

On a dull rainy day, the bridge was impressive but also somewhat lumpen. The massive lift towers have a considerable presence but the bridge did not appear elegant. However, there are some nice photos online of the bridge at night (taken from both ground level and from tower top), which show how attractive it can appear.

It's remarkable how much of the bridge has been left intact. It's easy to imagine that most of the steelwork is redundant, and due to its complexity, prone to corrosion and expensive to paint. However, it's not just the towers that remain in place, but the control cabin at midspan, and most of the lifting machinery including cables, sheaves and counterweights.

I guess that perhaps the main span is still largely supported on its counterweights, with only a small dead load reaction and all the live load reaction carried down through the span-end bearings. That will certainly have been the arrangement during its working lifetime, and it may have been too expensive to change it when the bridge ceased operating.


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12 November 2013

Teesside Bridges: 1. Middlesbrough Transporter Bridge


I was very lucky recently to join a weekend study tour of the bridges and structures of north-east England, organised by the British Group of the International Association for Bridge and Structural Engineering (IABSE). Previous British IABSE study tours had taken participants to Switzerland and France. I had greatly enjoyed the Swiss trip (and missed out on France), and wondered whether north-east England could possibly be anywhere near as interesting or enjoyable.

I needn't have been concerned. While much of the pleasure of the tour was the chance to meet and spend time with fellow bridge designers, it soon became obvious that we were to visit some splendid and fascinating bridges.

The first stop on the trip was the Middlesbrough Transporter Bridge. This is one of only six transporter bridges worldwide which remain operational (the others are in Newport, Bilbao, Rochefort, Osten, and Rendsburg). We visited it while it was closed for a major refurbishment (structural steel repairs and repainting), but were lucky enough to get a guided tour to the top of the bridge from the contractor, and of the machine house by one of the bridge's electricians.

The bridge was opened in 1911, nearly four decades after Charles Smith first proposed the concept of an "aerial ferry" bridge. Smith's idea was taken up by French engineer Ferdinand Arnodin, who designed several transporter bridges. The bridge at Middlesbrough, however, was designed by Georges Imbault, of Cleveland Bridge & Engineering Co Limited.

Unfortunately, we didn't have time to photograph the bridge from a proper distance, but most of the website links at the end of this post have plenty of photos. Seen in profile, it's a particularly fine structure. The four towers support cantilevering trusses, joined at mid-river by a hinge, and held down behind the towers by cables anchored vertically to the ground. It's the hinge that makes the bridge particularly attractive, I think. Several of the other surviving examples, particularly those designed by Arnodin, are suspension bridges with stiffening trusses, lacking the simplicity of the Middlesbrough design.

As part of the bridge's refurbishment, a lift will be installed at the south end, allowing more regular public access to the walkway level. The staircase that we climbed was steep and, on a windy day, terrifying enough for a group of hardened bridge enthusiasts, let alone the general public.


The trip to the top of the bridge, and the opportunity to quiz one of the engineers working on the refurbishment, was a great start to the study tour. Much of the repair and repainting work at high level is being undertaken from the upper transporter carriage, a high-level platform which rolls along the support girders and from which the bridge gondola is hung. This is both safe and reduces greatly the amount of temporary containment required when removing existing paintwork. However, several other parts of the bridge can be reached only with the use of roped access.

We also had a very interesting look around the bridge's machine house. As this was not in operation, most of the protective covers for the machinery and electrical equipment had been removed. What you can see in the photos is therefore quite different to what would normally be visible. It was particularly interesting to observe the difference between the original control panel, with massive fuses and electrical contacts, and the modern push-button panel.

 
 


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29 October 2013

Bridges news roundup

Ok, I've finished my series of posts on the bridges of Rotterdam.

I'll move on next to various bridges in north east England, the focus of a recent weekend bridges tour, but before I do, here are a few news items that caught my eye ...

Pedestrian Bridge / Miró Rivera Architects
I've probably posted a link to this bridge design before, but it's so great I won't get tired of it any time soon (see picture, right).

Olympic Stadium Amsterdam / René van Zuuk Architects
I think I don't like this bridge, but I'm really not sure.

'Location critical' for River Thames footbridge idea
Bridge proposed between Sunbury and Walton

New footbridge over city canal set to get go-ahead
New bridge at Speirs Wharf in Glasgow.

Revised footbridge designs for Greenwich Reach/Deptford Creek
Flint and Neill and Moxon are brought in to provide some much-needed common sense.

A bridge too far: Dozens of tourists plummet into lake after ignoring 'maximum capacity of 40' warning sign
Brand new footbridge in China unable to carry crowd loading. No serious injuries but plenty of photos of the collapse. The photos appear to show that the upper chord of the bridge truss initially behaved as a catenary, with the floor and lower chord peeling away from the truss web members, suggesting completely inadequate truss connections as the main cause of failure.

Foryd Harbour Bridge opens to public
Here's a nice aerial video of this bridge being opened to the public. According to the contractor's website, it cost £6.5m, which is a greater than 50% increase over the £4m budget stated when the design competition was held. Back in 2009, I said the bridge design was "like to prove a challenge technically, financially, and in achieving the desired programme", and I correctly predicted it would over-run on both budget and programme. I also thought it might prove unreliable in service due to the very unusual opening mechanism. I guess we'll have to wait and see whether that also proves to be true - it may not, as the "drawbridge" mechanism in the contest-winning design appears to have been replaced in the final structure with a more conventional hydraulic ram.

Third-party review reveals design concerns over halted Airport Parkway pedestrian bridge
Ottawa cable-stayed bridge is the subject of considerable embarrassment. A full copy of the critical review findings is online.
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28 October 2013

Rotterdam Bridges: 6. Willemsbrug


Of all the bridges I saw in Rotterdam, this last one is easily my least favourite. There's just something about it that is really, really boring. Apparently it won a Dutch Steel Award in 1983. I guess it must have been a quiet year.


Spanning 270m, and 33m wide, it is no small structure. When it was completed in 1981 it replaced a truss bridge dating back to 1878, which was also no small bridge.


The cable-stayed bridge form is one which offers designers considerable opportunities for creative input, so it's particularly disappointing that Willemsbrug makes so little use of this freedom. It's the towers, always the key feature on a cable-stayed bridge, which are the problem. Most cable-stayed bridges use a variation on either a portal-frame tower (sometimes H-shaped), or an A-frame tower (sometimes and inverted-Y). The Willemsbrug towers seem to be an awkward half-way house, somewhere between the two conventional options and with none of the grace of either.


The cables are arranged so that although they pick up the deck along its edges, in a "vertical" row perpendicular to the towers, they connect to the towers in a horizontal row. This requires the fan of the cables to twist in space. I guess it may have been done to create visual interest, because I can't see any other rationale for it, but it seems gratuitous and forced, and from some angles results in a very odd-looking layout, especially for the cables nearest to the towers.


As they enter the towers, the cables pass below eyelid-shaped cowls, which if they didn't disfigure the bridge enough, are accompanied by distracting access gantries. Given that there are access ladders within the towers, I can't see the point of this detail at all.


Overall, this must be one of the least visually successful cable-stayed bridges I can recall seeing, and it's a shame to end this whistle-stop tour of Rotterdam bridges on such a note!

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24 October 2013

Rotterdam Bridges: 5. De Hef


Officially called the Koningshavenbrug ("King's Harbour Bridge"), this bridge is nicknamed De Hef (“The Lift”) by the Dutch, showing a depressing lack of imagination. Why not “Stilty”? Or “The Old Rustbucket”?

This is a zombie bridge. The railway line that it once carried is closed, superseded by an underground metro. Accordingly, the bridge is left permanently open, its deck raised high into the air. It is lifeless, but as yet unburied. It survives as a gigantic memorial to the industrial era, and in that respect it offers considerable visual interest.

The two side spans were built in 1878, originally with a swing bridge in the middle. In 1927, it was replaced with the present lift bridge span, to provide greater shipping clearance. It closed to rail traffic in 1993.

When I first drafted this post, I spent some time pondering on how the bridge could be re-animated. Bereft of purpose, it seems unlikely to receive much in the way of maintenance, and could go the way of redundant relics like the Warrington Transporter Bridge, becoming a massive liability for its owner, with only one possible outcome.

I speculated on whether the bridge could offer a home to a modern restaurant, possibly dining al fresco, raising diners up above their surroundings to gaze at Rotterdam’s nightscape while picking listlessly at over-priced hors d’oeuvres. Mindful of the need not to annoy nearby residents by blasting out avant-garde dance music (the kind intended to drown out conversation and thus reduce the chance of awkward words spoiling an intimate meal), patrons would instead have to be entertained by a gentle dinner-jazz trio, adding soft tootles and burbles to the soundtrack of city streets.

As it turns out, I need not have speculated at all, as a local entrepreneur is already way ahead with plans to repurpose the bridge - Hef Experience Rotterdam. As well as access to an elevated public space and a museum, this originally proposed to include activities like bungee jumping and zip wires. From what I can gather, attempts to gain political and financial support have failed.

Perhaps some measure of why the proposal is not widely supported can be found in an article for Vers Beton magazine with a title which could be roughly translated as "Hands off de Hef". This argues that the structure should be left as a monument to industrial heritage, and that maintenance costs should be met by the municipality out of "moral duty".

I think I fall on the side of pragmatism - this will be an extremely expensive bridge to maintain in years to come, and without any source of revenue, there will inevitably be pressure to dismantle such a cumbersome and non-functional structure. Unless it is repurposed, it may survive only for so long as the cost of demolition exceeds the cost of maintenance.

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