27 February 2013

Kruunusillat bridge design competition: the entries (Part 3)

This is the last of three parts, concluding the entries to the Kruunusillat bridge design competition ... You can find more details on all the entries online, and there's a set of all the videos on YouTube.

Gemma Regalis
Most of the entries seem to have taken the view that the bridge should not compete visually with the relatively low-lying Helsinki skyline. This is the only one to buck the trend, with a single tall cable-stayed mast at its centre. The secondary spans are prestressed concrete on Y-shaped supports. The walkway is on one side of the bridge only, which I think is the best choice.

Recreatio Maritimus
This bridge is a sequence of very different experiences, with different structural forms to suit. At one end, there's a garden walk, with a tree-lined promenade carried on an arch bridge, and at the other the tramway and walkway are separated by a single central truss, supporting canopies on either side. This separation of tramway and walkway seems sensible, but it's far from clear why users would only want shelter at one end of the crossing and be exposed to the elements along the remainder. This design would also presumably require a substantial box girder below deck level to provide torsional stiffness, which detracts from the otherwise slender lines a truss can offer. On some of the shorter spans, an undulating spine girder provides the same separating function.

From an engineering perspective, I find this last entry by far the least convincing. The obvious question is why they went for a suspension bridge, one with twin 550m spans - there seems nothing about the site to suggest that multiple foundations in the water will be an issue for navigation or construction. The resulting design attempts to be slender, but requires additional stay cables and a massive under-deck truss to provide the necessary stiffness. Design of light rail bridges is governed by stiffness, and a suspension bridge is fundamentally ill-suited to satisfying this criterion. The concept reduces the number of bridge bearings and joints to a minimum, but at what cost?

26 February 2013

Kruunusillat bridge design competition: the entries (Part 2)

Okay, here's the second of three parts, continuing a quick run through the entries to this Finnish bridge design competition ... You can find more details on all the entries online, and there's a set of all the videos on YouTube. The first part is here.

Filum Lucis
I can see this design being unpopular with many of the people who tend to comment on architecture blogs and websites, but I like it. The bridge is a simple post-tensioned concrete box girder, cast in-situ, and intended to offer the most minimal line possible across the site, something which seems highly admirable when set against more attention-grabbing schemes.

Unda Arctica
This is one of my favourite designs, with a very elegant series of "undulating" arches, the arches above the bridge deck separated by reverse arches below the deck. Although that's visually attractive, it isn't structurally rational, with the reverse arches subjected to much higher bending loads than is desirable. Pedestrians and light rail are each allocated to once side of the deck, avoiding the separation of pedestrians into two streams that some of the other designs require.

In the previous post, I featured one design where the pedestrians and light rail vehicles were both tucked away inside a sheltering truss structure; and one where the light rail was sheltered inside the truss but the pedestrians exposed to the weather on an upper deck. Occursus offers a hybrid of these solutions, with the light rail on the steel truss's top deck, but pedestrians free to use either level, possibly according to the weather. I can't help thinking that most of these designs pay too much attention to the pedestrian users: this is a bridge over 2km long, which to me seems an excessively long, narrow corridor for walkers, although it's very suitable for cyclists. Won't most bridge users simply take the tram?

Septem Fratres
At first sight, this entry is very similar to Nexu, which I covered in the previous post. This one has seven central cable-stayed towers with 130m spans, while Nexu had six towers and 160m spans. The text for Septem Fratres describes it as an "extradosed" rather than "cable-stayed" bridge, which just means that the towers are of lower height and the cables at a shallower angle - it's a halfway house between cable-stayed and post-tensioned box girder bridge. The lower profile is one attraction, but I also prefer that on this option the main pedestrian route is all on one side of the bridge.

25 February 2013

Kruunusillat bridge design competition: the entries (Part 1)

I thought I'd do a fairly quick run-through of the 11 entries to Helsinki's bridge design competition. You can find them all online, with more images than I'll show here, and there's a set of all the videos on YouTube.

The entries are submitted and judged anonymously, and have all been given odd Latin names for ease of identification. There was a list of ten entrants in my previous post, I don't know why there are eleven entries on display. Here's that list again:
  • 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
Here are the first four designs, I'll continue with others in later posts:

With its series of repeated cantilever / stayed steel modules, this bridge reminds me of Riccardo Morandi's Lake Maracaibo bridge. That concept belongs to a long-dead period of stayed-bridge design, overtaken by methods involving larger cable arrays which are cheaper to erect. The position of the steel stays doesn't appear structurally rational - the obvious point to connect to the deck is at the third-span points, not near the centre. Visually, it is highly distinctive, and not so tall as to be overbearing.

The Nexu design is the more conventional version of the first proposal, with a single row of pylons in the centre of the deck and a conventional central band of cable-stays carrying the deck. Its sense of discretion appeals to me, it appears to be trying to fit into the landscape rather than distract from it. Viewing the video, you can see two cycle/footways, one on each side of the central tramway. I don't think this is ideal for such a long bridge - users travelling on foot should all be able to mingle in one walkway area.

Debet Semper Plus Esse Virium In Vectores Quam In Onere
I think this is easily the most interesting entry, a hugely elongated covered bridge intended to provide shelter to users throughout the year. Pedestrians walk on a central raised platform, with tram tracks either side. A diamond-faceted shell provides the enclosure. It's hard to decide whether the lack of visibility and exposure to the landscape is a price worth paying for the provision of shelter. I'm unclear why the shelter needs to cover the tram tracks - it would be less expensive, and easier to maintain, if only the central spine were covered, and the tramway left exposed to the elements.

Over much of its length, this design separates the tramway from pedestrians by locating the walkway on the roof of the main truss girders. This may have advantages in terms of providing views, but as with the previous design, it leads to a very deep structure overall. Unlike the previous design, the trams are sheltered and the pedestrians are not, which may seem perverse in poor weather. The truss girders are not steel, but in ultra-high performance concrete, prestressed to give it the necessary tensile strength (it is otherwise a material very similar to cast iron in performance). This is innovative, but high-risk - I don't believe UHPC has been used in this manner or scale before, and while the concrete will be durable, there are a large number of very short prestressed members, which is not efficient to assemble, and construction may be expensive, as some forms of UHPC require steam-curing to achieve their best properties.

22 February 2013

River Wear Bridge controversy linked to IABSE competition guidelines

"When engineers get the knife out they can be worse than architects". So says an editorial from Paul Finch in this week's Architects Journal. Finch suggests that "all is not happy in that part of the engineering world which still believes that dreary Freeman Fox box girders were all that were ever required."

The target of his scorn is criticism by bridge engineers of the design for the New Wear Crossing in Sunderland (pictured). The scheme, which has experienced a history of uncertainty dating back to the original bridge design competition, has recently suffered a major blow when two of four tenderers pulled out, almost certainly because of the difficulties determining the cost of building such an unusual structure with sufficient certainty.

Finch asserts that criticism of the "handsome-looking" bridge has been "aggressive" and "moaning", going on to request that "serious competitions with serious winners should not be the subject of professional sniping."

Really? How absurd. Perhaps an appropriate title for this blog post might be "When journalists get the knife out they can be worse than engineers or architects", and perhaps a humble blogger might suggest that "serious engineers should not be the subject of sniping from amateurs".

Although never named, the target of Finch's attack is Simon Bourne, probably the only engineer willing to have his name publicly attached to criticism of Sunderland's vanity project. He has gone on record at least twice. I reported the first occasion, when he told New Civil Engineer that "the bridge is about as structurally inefficient as you can imagine", which strikes me as essentially uncontentious. Two other, anonymous, engineers were happy to attack the bridge at the same time, and these views are consistent with most if not all of those which I have heard privately from other bridge designers. Bourne's more recent comments, in response to the withdrawal of two tenderers, included saying that "the risks of its hugely unique nature are very profound", which strikes me merely as a statement of the obvious.

In Finch's world, engineers should presumably just shut up and fall in line, leaving architects to do the talking. As I've discussed here before, deafness to criticism aligns closely with clients buying closely into a designer's vision, blind to its faults or at least to its risks. At least one high-profile UK bridge design contest came to a miserable end as a result, with a structurally exotic proposal remaining unbuilt, and it's now increasingly possible that the same will happen in Sunderland. Criticism should be welcomed: if a project is well-thought through, responding to challenge will only make its case stronger. What is less helpful, and Bourne's comments fall into this category, is criticism which comes too late to actually make any difference to the decision-making. Participants at all levels have too much personal investment in a project, and positions are too entrenched to change. Careers are staked on making a project succeed, whatever it takes, regardless of whether simpler or better-value alternatives have been discarded along the way.

Finch's attack on honest criticism doesn't end there, however. He goes on to link his point to IABSE's Guidelines for Bridge Design Competitions, which were published earlier this month. This is a document which grew out of widespread dissatisfaction with the conduct and outcome of design contests. In the UK, the subject was extensively aired at the 2007 IABSE Henderson Colloquium, with many of the lessons identified from failed competitions finding their way into the final IABSE guidance.

Finch points to an interview with Naeem Hussain, the chair of the IABSE bridge design competition working group, who discussed the guidelines with New Civil Engineer last year, prior to publication. Hussain was quoted by NCE as saying: "Some of the architects themselves are saying that the pendulum has swung too much and that designs are becoming so outlandish. First you often cannot build them or then the cost is so high that the client abandons the project." The IABSE guidelines are intended to assist clients in properly appraising proposals at the outset so as to reduce the risk of failure, and hence the risk of contest participants wasting their time and money.

In addition to a number of rather petty side-swipes at the content of the guidelines themselves, Finch suggests Hussain's NCE interview "reads like a thinly veiled attack on ‘arty’ structures." Finch isn't wrong to put his finger on the anti-expressive nature of many engineers, a belief instilled by their training and culture that value is the same thing as economy, and that measuring efficiency is tantamount of measuring virtue. I have limited sympathy with this reductionist vision of what bridge design can and should be, but nor would I suggest that the genuinely held views of acknowledged bridge construction experts should be discarded simply because a design competition was somehow "serious", as Finch does. Indeed, I think their views on the subject are probably better-informed than non-professional commentators.

A desire to silence engineering criticism has been reported within the New Wear Crossing's project team itself. In a talk by the design engineer Techniker, reprinted on their website, you can find the following: "One engineering collaborator on the project simply had to go – [they] proved to be subverting the intentions of the designer as at odds with appropriate bridge design. This was a kind of negative professionalism, parochial and ingrowing." Perhaps this is the same anonymous party cited by NCE last year as 'an expert close to the project', saying: "It's a really complicated bridge, and completely unnecessary for a span of this length".

I would have to agree with Techniker, in part. If a professional firm engaged on the project is genuinely attempting to do anything other than use their best professional endeavours to help deliver the client's agreed vision, then they should not be there. The rest of Techniker's talk makes clear that their view is that this is a cultural problem, that many engineers are trapped in what Finch would parody as the box-girder mindset.

More of Techniker's perspective can be understood from a short blog post on their website, which claims that "with modern methods of analysis construction practicalities are receding into irrelevance and the architect is free to organise form as he/she wishes within the geometric constraints of stability." I imagine many contractors would beg to differ, not least the two who have withdrawn from the procurement process.

Techniker's view appears to be simply that some necessary material has been moved up into the sky out of the deck, and if you think I am caricaturing them, here is how they describe the design process: "We worked to justify our proposals as a bigging out of the required steel, spreading it across the sky to make an effect." This is the opposite of the traditional bridge engineering approach, which works from the constraints of the site and of the construction method to determine where material can most efficiently be used. Cable-stayed bridges, of which the New Wear Crossing remains at heart an example, are the epitome of this conventional approach, incorporating within their permanent form all the materials that are also required for temporary support. The River Wear bridge, by contrast, will require extensive temporary support during construction, as material has been disposed for primarily expressive rather than structural effect. Some of the consequences can be seen in Techniker's website postings, and also on their detailed design drawings, a grab bag of which have just been made public.

A departure from the ordinary engineering imperative can be economically justified wherever the outcome creates sufficient value to offset the additional expenditure. That's the argument made by Sunderland Council's leader, who in defending the iconic design makes a big noise about the whole scheme's benefit-to-cost ratio (BCR), which is over 4, and therefore far more positive than many other schemes which government is happy to support. The breakdown of the calculated BCR can be found in a document on the New Wear Crossing website (see in particular page 63).

This makes clear that nearly 90% of the expected benefit of the project relates to transport cost savings, with only about 10% relating to the "landmark" nature of the bridge scheme. Of that remaining 10%, the majority relates to the expectation that an "iconic" structure will attract more investment and create more jobs than a cheaper alternative, a belief widely accepted but one for which hard evidence is much harder to come by. What is less clear, and I have been unable to extract numbers from Sunderland's reports which test this, is whether the additional "landmark" benefit is commensurate with the additional cost of a landmark versus a cheap structure. On the figures presented, any "extra over" cost of making the bridge "landmark" rather than conventional, beyond an allowance of £8m, will actually imply that choosing a landmark has reduced the benefit-to-cost ratio of the whole scheme. It doesn't seem plausible to me that the "landmark" cost of this bridge (as against Paul Finch's hated box girder option) is that low.

Ultimately, this is one proper test of the design's appropriateness. Does it add a sufficient proportion of value to justify its cost? While the scheme's engineering critics are right to point out the risks and difficulties of taking forward such a monumentally unique design, they have little if anything relevant to say about the value of the resulting structure to Sunderland's economy.

In one of their website postings, Techniker assert: "We need to set up a critical framework for engineering." This is quite right. Such a framework won't be found solely in the engineering puritans' fear of extravagance; nor in the belief that the desire for economy is irrelevant in an era where anything that can be designed can be built. It certainly won't be found in a world where honest engineering views are dismissed out-of-hand by journalists as "sniping" or "moaning", nor one where IABSE's well-intentioned attempt to encourage better procurement is treated with unjustified paranoia.

20 February 2013

Kruunusillat bridge design contest entries revealed

The eleven entries to Helsinki's Kruunusillat light-rail bridge design competition have been made public. They are being exhibited locally, and can also be found on the internet.

If I get time in the next few days, I'll post some of my own thoughts, but feel free to comment here.

15 February 2013

"Dorfbrücke Vals" by Wilfried Dechau

The modern bridge designer is only rarely a solitary individual. Most designers, however personally creative they may be, are part of a team, and in the case of the largest bridges, a very large team indeed. This is an inevitable feature of the complexity of both the structures designed and of the process whereby design is conceived, refined, and detailed. One result is that many fine designers are effectively anonymous – it’s rare to be able to point to a bridge and to know who the lead designer was, and particularly rare to imagine that even if you did, you have identified someone who was the key driving force behind all aspects of the design activity.

This is perhaps one reason why the Swiss bridge designer Jürg Conzett is such a significant figure. He is the descendant of a remarkable line of Swiss bridge nobility, most notably Robert Maillart and Christian Menn, men who married clear aesthetic vision to a deep intuition for structural principles, and a pragmatic taste for craftsmanship. It would not be unfair on the rest of the modern bridge design community to note that Conzett is a bridge design genius. I am sure he would be the first to admit that the bridges credited to him are also the product of considerable teamwork, but they do give the strong impression of the hands-on involvement of an auteur at every stage.

The Pontist has been fortunate enough to visit two of Conzett’s best known bridges, the Punt da Suransuns, and the Traversinersteg, both in the company of the man himself. These are lightweight, high-tensile structures, exploiting the anchorage capabilities of Swiss mountain bedrock to create undoubted masterpieces. The second of these was considered sufficiently noteworthy to be the subject of a marvellous photo-book by the excellent German photographer Wilfried Dechau, documenting its seemingly perilous construction high over an Alpine ravine.

I have not had the pleasure of visiting Conzett’s more recent structures, which include a new highway bridge in the centre of Vals village, a place best known to architecture fans as home to Peter Zumthor’s thermal baths. Luckily, it too has been documented in another splendid Dechau photo-tome, Dorfbrücke Vals – Photographic Journal (Wilfried Dechau, Ernst Wasmuth Verlag, 144pp, 2010) [amazon.co.uk].

As with its Traversinersteg sibling, the book is a delight to hold, housed in a high quality slipcase and filled with marvellous photographs. These are accompanied by several illuminating essays. Klaus Siegele discusses the centrality of water to Vals, a village built on the banks of the Valser Rhine. As well as the thermal baths, the village is also known for its mineral water. However, it is the propensity of the river to flooding which led to a decision to replace the existing river span, a life-expired metal truss.

Patrick Hannay contributes an essay which manages to put the bridge in the context of other Conzett projects, of Swiss stone, and even of Tolkien’s bridge in the Moria caverns. Ursula Baus interviews the architect Zumthor , who chose the appearance of the flood walls and set the basic parameters for Conzett’s design – that the bridge should be an arch, and that it should use local Vals stone. Conzett himself discusses the bridge’s structural engineering, as well as that of two nearby footbridges, the Milchbrücke and the Rovanadabrücke, which formed part of the same project.

I will confess that I have a general understanding how the Dorfbrücke (“village bridge”) works structurally, but am not entirely sure I understand all the details. The deck is a reinforced concrete slab, spanning transversely between two concrete edge beams, which are post-tensioned. These form the tension member, or “bow”, in what must be the world’s least conventional bowstring arch bridge. The arch is formed of radially placed stone slabs, above the deck but resting directly upon it (there’s no gap between deck and arch, because these bridge side walls also serve to hold back floodwaters and prevent it from spilling it out onto the village roads). The deck is then hung from the stone arch by means of a series of concrete “fingers” which penetrate the stonework.

The result is a bridge of exceptional structural ingenuity, but not one which has immediate visual appeal. It is certainly not elegant, with the stone side walls towering above head height – there are no views of the river from it. It is a bridge as a confining corridor, rather than as a platform from which to admire its surroundings. It channels views towards the village church at one end.

Its visual appeal is not far from that of brutalism, the 1960s and 1970s architectural trend towards robust, unadorned concrete in stark, simple geometry. It is a blunt instrument, saved mainly by the attractions of the finely cut local stone, and the general sense of craftsmanship which is one of Conzett’s hallmarks. It won’t be remembered as his finest bridge, but it is as structurally remarkable as the others.

Dechau’s photographs depict the finished bridge, but concentrate for the main part on a record of its construction, including the demolition of the old bridge, and a number of photographs of the site workers and of curious onlookers. Several photographs range beyond the bridge to depict the mountain streams which feed the river, and a nearby dam, a towering concrete monolith.

Certainly, Dorfbrücke Vals – Photographic Journal is a book for collectors and connoisseurs only. The more casual reader may prefer to await a broader overview of Conzett's career. But it is a very well-matched companion to this otherwise inscrutable bridge, bringing to life the story of its construction, and I enjoyed it.


06 February 2013

Manchester Bridges: 22. Spinningfields Footbridge

This is the second of two new footbridges over the River Irwell, connecting central Manchester to neighbouring Salford. I covered the other one in the previous post.

Neither bridge could be justified on a cost-benefit analysis of journey time saved. Greengate Footbridge is particularly absurd in that respect, being only 5m away from an existing foot-accessible bridge. The £1.5m Spinningfields Footbridge is a little better, shaving maybe 3 or 4 minutes off a journey walking across the nearest existing bridges (Bridge Street to the north New Quay Street to the south). However, both bridges act as gateways, as ways to improve the permeability of the urban fabric, enhancing the feeling of accessibility as much as the reality of it.

Greengate Bridge's minimalist appearance shows the structural engineer in full retreat, a functionary whose role is quite literally to support the architectural vision with as much discretion as can be mustered. Sited between Greengate and Spinningfields, Santiago Calatrava's Trinity Footbridge is the exact opposite, the structural engineer as flamboyant showman, the centre of attention.

Spinningfields Footbridge lies somewhere between the two extremes. The structural engineering takes centre stage, but not at the visual expense of everything else in the immediate vicinity. It's a very sophisticated piece of engineering, but retains a sense of modesty and a great deal of elegance. I reckon it's the finest contemporary footbridge in Manchester, and one of the best in Britain.

Designed by Ramboll (based on appearance, their former Whitbybird team rather than their former Gifford team), this is a design that distils many years' bridge design experience, matching a simple and beautiful overall concept to a super-careful attention to detail. It was built by Eric Wright.

The River Irwell at this point has high banks and so far as I can tell is not regularly navigated, nor prone to flooding. This gives designers the opportunity to "hide" all the bridge structure below deck level, something that is not always an option. Ramboll have used that as a cue for a lenticular form, deepest in the middle where the highest bending forces are found.

I described a generally similar bridge in Manchester two posts back, and discussed how the form can be seen in several different ways, one being that it is an "under-spanned" self-anchored suspension bridge. This is like a normal suspension bridge but with the suspending cable below the bridge deck rather than above it. Instead of being hung below the cable, the deck sits above it on struts. Instead of the main cable's tension force being anchored into the ground, it is anchored to the bridge deck itself, which therefore must resist compression. It's a design which can sit much more lightly on the ground than the normal suspension bridge.

Bridges of this type can be prone to torsional flexibility, a tendency to twist. I've seen several designs where the deck and cable are connected by a triangulated structure to create a skeletal "torsion box" which can resist this twisting – indeed, the Leech Street Footbridge is of that type. The Spinningfields bridge is considerably more adventurous.

The key feature of the bridge is that it is curved in plan, as is the supporting cable, although it follows a different line. The two are connected by individual struts, with no triangulation. The struts themselves are of folded steel plates, giving them necessary stiffness, and this is cleverly integrated with folded-plate deck bracing. There are clear echoes here of the ribbing on Lune Millennium Bridge (by the same designers), which I featured here not long ago. I have to say that I find it startling that so trimmed-down a structure is stable, and would need to see the engineering drawings to really understand how it works.

The Y-shaped parapets and the knife-edge fascia are reminiscent of the Chelsea Bridge Wharf Link Bridge, yet another Whitbybird / Ramboll design, and in my view are very attractive. Lighting is incorporated into the handrail, and there's further lighting below the deck level to illuminate the bridge structure at night. The triangular fascia does a great job in making the edge of the deck look extremely slender. The decking is permeable aluminium sheeting, allowing rainfall to drain freely through to the river.

I found vibration to be quite perceptible, although the amplitude is low enough not to cause any distress. Feedback on the Skyscrapercity website indicates I'm not alone in noticeing the movement.

A seating bench is provided on the deck, which I guess may make it a popular sandwich or smoking spot for workers from nearby offices. The deck is up to 4.5m wide, which is pleasingly generous.

Overall, I think this a real gem of a bridge, structurally daring yet in no way ostentatious, and one which deserves wide recognition.

Further information

03 February 2013

Manchester Bridges: 21. Greengate Footbridge

Britain’s major cities can be divided into those with a strong connection to the underlying landscape, and those where the landscape has been obliterated or appears featureless, lending a decided lack of character to the urban fabric, which architecture and town planning struggle to rectify. In the former camp are the river cities, London, Bristol, Newcastle and Glasgow among them, where a major river was the reason for the city’s existence and continues to anchor its layout, as well as those with central parkland, such as London (again), or Edinburgh (the latter particularly well-blessed in this respect). In the latter camp you will find Birmingham and Manchester, city centres defined primarily by the relationship between their shopping centres and railway stations (or worse, by an inner ring road).

Manchester appears to have recognised this deficit for some time, with a long-held desire to shift commercial and leisure activity westwards, into the less economically sensitive Salford, in the process reconnecting to the city’s main natural waterway, the River Irwell (which defines the Manchester / Salford boundary). I’ve previously visited Santiago Calatrava’s Trinity Bridge, a typically elaborate structure which spans this river and which sought (with, I think, limited success) to trigger riverside regeneration.

There’s no real shortage of road crossings of the River Irwell, but successful development in Spinningfields on the river’s east bank, and the planned Greengate development on the river’s west bank, have triggered the construction of two new footbridges within the last year. These form part of a wider River Irwell masterplan intended to make it a far more central feature in city life, including the construction of new riverside paths and walkways.

In this post, I’ll cover the recently completed footbridge which forms a gateway to Greengate, and in my next post I’ll address the bridge at Spinningfields.

The Greengate footbridge has been built to the north of Trinity Bridge. Its east end sits close to Manchester Cathedral, and its west end spills out towards a new plaza area which I assume to be the first part of the as-yet unbuilt Greengate scheme.

It appears to be something of an unnecessary indulgence, sitting as it does no more than 5m away from the existing Victoria Bridge, which already provides a perfectly serviceable foot crossing of the river. Evidently, the Greengate developers don’t see that as a suitable entrance to their grand scheme, and I can certainly imagine that the lack of a new bridge would enhance the sense of the development as peripheral to the city centre, rather than as a continuation of it (much of the area on the Manchester side was re-developed following the 1996 IRA bombing, but this stopped well short of the riverside, a missed opportunity).

The river here sits deep below the surrounding streets, particularly the east bank, and consequently there is no structural rationale for supporting the structure from above. The designers therefore had to use other means to create the sense of a gateway, and these relate mainly to the quality of the finishes on what is, by any standards, a very minimalist contemporary design.

From many angles, the bridge structure seems almost to disappear, something enhanced by combining generous overhangs on the concrete bridge slab with inclined faces to its supporting spine girder. This means that you have to walk some distance beyond the bridge before you can see its primary structure at all.

The spine beam is a steel box girder, which supports a series of precast concrete deck slabs. The bridge abutments are hidden behind the existing riverside wall facing, enhancing the overall impression of minimalism. I can imagine the foundations to have been significant challenges, particularly on the east side where it can be seen that the riverside wall is actually voided in construction, with a series of arched recesses visible.

The bridge has structural glass balustrades topped by stainless steel handrails. The balustrading extends beyond the bridge at both ends, and defines it as merely the opening element in the plaza’s hard landscaping. The result is a very contemporary design. I guess that at night it may merit a “blade of light” description, although I haven’t been able to locate any night-time photographs.

A typical question with all-glass parapets is their susceptibility to vandalism, and the ensuing cost of occasional replacement panels. As a result, they are usually limited to well-policed internal use, in shopping centres and similar settings. Time will tell how well they survive in the Manchester / Salford city centre.

I haven't been able to find any information on the bridge's designer, contractor, or cost, so if anyone can provide further detail, please post in the comments.

Further information