27 May 2013

River Wear - A Bridge Too Far

As a follow-on to the last post, I found some interesting commentary on the River Wear bridge at New Civil Engineer's website, posted by long-time critic of the bridge, Simon Bourne. With Simon's permission, I am reprinting it verbatim here, and I would be interested to receive comments.


River Wear - A Bridge Too Far
I have two well-known points regarding this scheme – the first is the cost, but my main objection is actually the complete lack of structural integrity, which is also at the heart of two other concerns about the quality of design and of designers.

1. The Bridge Costs
There are several facts about the costs of the Wear Bridge – facts which, it seems, have not been made available to the client, the residents of Sunderland or the major funder, i.e. the Department for Transport (DfT). One can show very simply that a high-quality and elegant bridge at this location should cost no more than £15-20m.

At the specialist bridge design consultancy that I used to own, Benaim, I have seen the design and construction of two recent bridges of very similar size and location. Both were of similar width (~25m) with one being a little longer (450m) and one being a little shorter (300m). The shorter one had considerable architectural input from a very well-known UK bridge architect. The shorter one cost about £10m and the longer one about £15m. On this basis, and with some adjustments for size and inflation, a high-quality bridge at Wear should therefore cost about £15m. Even with some further sensible premium applied (which I discuss in Section 3), the actual bridge cost should be no more than £20m.

However, the exhibited cost of the bridge is £55m – a factor of nearly three has been adopted. I would suggest that a premium of this size is wholly unacceptable, at any site. This figure may also yet increase further as the real complexity of the construction becomes revealed. This baseline cost of £20m equates to about £2,000-2,500/sq.m, which seems very reasonable compared to all other bridges of its size, a little on the high side if anything. The exhibited scheme though has a cost of around £6,000-7,000/sq.m, which one only finds amongst the very largest and most complex bridges in the world (i.e. major world bridges with spans close to 1,000m that are complex through the engineering necessity of their span, location and scale).

By the time one adds the costs for the highways (~£25m), land (~£10m), fees (~£15m) and the same level of risk/inflation (~£10m), the total cost of the scheme becomes £80m, not the £120m that defines the current scheme. So, the saving attached to a baseline, good-quality solution is thus £40m, not the £5-10m that seems to have been quoted. It would appear that the client, the local residents of Sunderland and the DfT (who provide ~£85m of public funds) are not aware of this potential saving.

It is also noteworthy that around £15m has been spent in fees (over the last 8 years of development since the design competition in 2005) – a figure that is equal to the actual cost of building a sensible bridge.

The original budget for the scheme in 2005 was around £40m, which would suggest that £15m for the bridge was originally expected – this £40m budget has now increased to about £120m. Any publicly-funded scheme that clearly struggles to progress or has a budget that escalates so wildly should certainly be held open to considerable public scrutiny.

2. The Lack of Structural Integrity
The scheme is at face value a cable-stayed bridge, but the lack of connection between the two towers completely transforms the behaviour of the bridge, from elegant engineering in to utter chaos. The two towers are now forced to carry the cantilever moments from the front stays, instead of simply being a means to spread the forces in to the obvious back stays. The public might not appreciate the enormity of this distinction – so, I liken it to a plane being designed with only one wing. Of course, the engineering can be applied to solve even this problem, though the size needed for the jet engines would surely make the plane fly more like a rocket than a plane. This one-winged plane would be a ludicrous piece of engineering, at very high cost – but that is effectively what the Wear scheme has become.

The Wear Bridge has many similarities to Calatrava’s Alamillo Bridge in Seville, which is also an unbalanced cable-stayed structure. I know that this bridge also cost about three times the price of a more traditional solution. It was justified at the time as being part of the development for the Expo 92 in Seville. Though I can support a premium being attached to a bridge that was built as part of Expo 92, and one can observe that the Alamillo Bridge has indeed also become an icon for the city, I cannot support any scheme that has such a high premium (see Section 3).

There is also a common misconception that the two towers of the Wear Bridge are steel fabrications, with a length/width about 5m. They are not anything like this small. Each 140-180m high tower is equivalent to the largest concrete bridge cantilever in the world – the same scale as the 301m span Stolma Bridge in Norway. Each tower is a prestressed concrete box girder around 15-20m deep at its base and about 10m wide, with 1m to 3m thick walls and prestressed with about 120 prestressing cables. I estimate the prestressing force in each tower is around 500MN, i.e. 50,000t, with the tower having to carry a moment of around 7,000MNm – enormous figures that are consistent with the enormity of the task in hand.

The bridge in reality only needs to have 50m spans, or perhaps an elegant 100m cable-stayed span – it does not need to have the equivalent of a 300m span. Not only does the scheme provide a concrete box girder (in the two towers) that is the same as the largest concrete beam bridge in the world, but it then also provides a completely separate steel-composite deck and a complete set of cable-stays to connect the two systems. The scheme effectively has three bridges in one – and so it is not surprising that it costs three times as much.

3. The Quality of Bridge Design
Every bridge or piece of infrastructure should, of course, be a fine piece of engineering of the highest quality. But that desire does not have an additional cost attached to it, and every piece of infrastructure cannot have a premium anyway. However, there will be selected number of major bridges or pieces of infrastructure that do deserve a premium. Society has to decide what premium is acceptable and where or when it is applied, and engineers and architects as representatives of society should formulate those figures. As you can get well-designed bridges at little or no premium, these should be the norm.

At certain key sites (major estuaries, major cities or bridges of national interest or certain bridges with considerable traffic) or at certain key times (the Olympics, for example), one could suggest premiums of 10-25%, say. Most major bridges are dominated by their engineering and environmental challenges, and it is nearly always the resolution of these issues that defines the beauty and success of the bridge. The huge majority of the world’s most fabulous bridges had no premium applied to them and had no architectural input – consider my favourites such as Brunel’s Saltash Bridge across the River Tamar, or Maillart’s Salginatobel Bridge in Switzerland or Freeman Fox’s Humber Bridge.

More recently, architects have indeed become involved, which can be a very welcome addition as long as that architect is skilled in bridge design and respects the considerable forces at work within the bridge. Architects also bring a wider appreciation of social and environmental issues, which can be fundamentally important too.

So, I can see the need for every bridge to be well engineered and carefully designed, with architectural input as the engineer needs it, and the need for a certain number of key bridges to have a premium attached to them, but I cannot see the need for a premium of 2 or 3 to be applied, at any site. It might be possible to play some architectural or sculptural games, or some structural gymnastics with a £2-5m footbridge, where a significant premium might thus be applied, but it is certainly never acceptable to do the same for a £50-100m piece of infrastructure. A footbridge is often more akin to a building, with a shorter lifespan, fewer concerns over its long-term integrity and it is often privately funded. A major bridge though has to last well over a 100 years, be virtually maintenance-free for the same period and justify its existence using public funds.

The client at Wear suggests two reasons for his selection of this scheme – the artistic merits, which I dismiss as they have led to nothing other than a complete lack of structural integrity, and the economic advantages of a landmark bridge. The vast majority of the economic benefit of the scheme lies in the building of a road and a bridge, any bridge in fact. The rather nebulous benefits regarding the further advantages of a landmark scheme are desperately difficult to define and hard to validate, and it is equally hard to find any supporting evidence of such benefit. One has to question the desire of the client to seek a landmark scheme so strongly.

Any publicly-funded client should be seeking to procure a high-quality scheme that fulfils its purpose – the premium to be spent on anything further, such as a landmark solution, should be proportionate to the needs of the area or the value/benefit of the scheme. The client seems to believe that a further £10m benefit might accrue from the creation of a landmark scheme, a scheme which he understands to cost about £5-10m more – that balance might thus make sense, if it were all valid. However, the further benefits of a landmark scheme might equally be zero, and we know from Section 1 above that the additional cost of the landmark scheme is actually around £40m, or more – the cost-benefit equation now makes no sense at all, but the funding authorities do not seem to have appreciated this point yet.

4. The Quality of Bridge Designers
Bridge designers have to use their client’s money wisely as well as leaving an elegant legacy for the benefit of society. I welcome the involvement of skilful architects in this process and indeed the majority of my major bridge designs (many of which have won awards for their elegance, economy and innovation) have been developed with specialist bridge architects – architects who understand the engineering and construction principles, and who work with the engineer to develop forms and details that improve the legacy that we leave behind for society.

In the last 20 years, architects with good bridge expertise have also joined many other engineering teams that design both major and minor bridges, mainly because engineers often do not have this level of aesthetic training or knowledge of the social impacts. This liaison with skilled architects is certainly to be encouraged as it will raise the overall quality of the scheme, generally at little or no cost though. My favourite bridge of the last 20 years, Virlogeux’s Normandy Bridge, rightly had good architectural input too, and the current crop of major bridges (such as the Millau Viaduct in France, the Stonecutters Bridge in Hong Kong or the Forth Replacement Crossing) have also had significant architects involved as part of the design team, though clearly the engineering still dominates with all these schemes.

The key is for the architect to be experienced in bridge design and for their role to be proportionate. On a building, the structural content might only be 25%, and as such the architect leads the design and the engineer supports as part of the team. However, for a bridge where the structural content might be 90%, the engineer must lead and the architect should provide support. On all the major bridges where experienced bridge architects have been involved, they have worked with the engineering to develop overall forms and particular details that work well. On a few occasions though (often with footbridges and rarely with major infrastructure), architects have ignored the engineering and developed their own forms – the Wear Bridge is exactly a case in point.

One has to query the reasoning behind this client appointing a team that seems to have had little major bridge experience. A client commissioning a new hospital or airport would clearly seek an architect, and an engineer, with substantial experience in the design of such buildings. A well-informed client for a major new bridge should only seek an engineer, and an architect if needed, who also has substantial experience of major bridges. Michel Virlogeux noted last month about how the demise of a central client authority in France will lessen the likelihood of further spectacular bridges in that country.

Though I do not entirely support that view (on the basis that design and construct schemes can indeed deliver excellence in all areas – elegance, economy and innovation), it is a good point that the procurement of major schemes can often be best managed when that client body is a national body, with extensive experience and knowledge, the ability to best judge when and where a premium should be applied, and who has control over, and a vision for, the design direction. This would avoid the one-off procurement by a less experienced client, who might be blinkered by his own desires to create an unnecessary and expensive landmark.

I hope that the funding authorities for this scheme (both Sunderland City Council and the DfT) appreciate the enormity of the task ahead of them, with all its attendant risks, and begin to realise that there are very satisfactory, and high-quality, alternatives that are available to them for at least £40m less. A more appropriate scheme of this nature could still be delivered, for the benefit of the whole Sunderland community, more quickly and reliably.

The architect’s role in bridge design is definitely to be encouraged, but that role must be proportionate to the dominance of the engineering forces at work, and that architect must have valid major bridge experience. All infrastructure and bridges must be well-designed and of high quality, with a number of key national projects being worthy of suitable premiums. A central national authority to manage the procurement and design direction of these key projects would make good sense – the DfT would seem the obvious candidate for this role given that they are also the prime source of public funding in this area.

By Simon Bourne, March 2013, reprinted from the New Civil Engineer's website.

23 May 2013

River Wear Crossing tenders returned

Tenders were due in for Sunderland's River Wear crossing on 22nd May, and presumably they have now been received. The tender date had been delayed twice, having originally been set as 20th March, and then extended once already to 24th April. The number of tenderers had also dropped, from the original shortlisted four, down to two, after Ferrovial and Balfour Beatty withdrew, leaving the field to Vinci and Graham.

While the bridge building world waits to see whether either tenderer has actually managed to come in below Sunderland Council's £118m project budget, I thought I'd post up a couple of items that are relevant, one in this post and then another to follow soon.

I posted a lengthy update on progress with the bridge almost exactly a year ago. Now, the bridge's lead structural designer, Techniker's Matthew Wells has responded to my post in the comments section.

Wells asks for the bridge to be judged distinctly in architectural, engineering and commercial terms. On the engineering, he notes that "the engineering has been involved and very enjoyable. My associates have demonstrated outstanding skills to realise it", which I don't doubt. Commercially, he says "Is it value for money? Perhaps best left to the client to judge where to spend his/her money." There, we part company. I've argued here in the past that the value a landmark bridge brings to its community is very poorly understood, even in purely economic terms.

Sunderland Council commissioned specialists to put a figure on the value a landmark bridge offered, particularly in how it could encourage investment and hence enhance employment, but this was long after the decision was made to press ahead with the "iconic" design, and comes across somewhat as post facto rationalisation put in place to keep central government funders happy. In short, I believe very few clients can present any real evidence to justify how they spend taxpayers' money once things move beyond simple journey-time benefits, and even those are often grossly miscalculated.

Wells also comments that "like all bridges, it's for 120 years, so questions of design in austerity need careful consideration". Here it may be appropriate to consider that this was a bridge conceived in 2005, at a time when Sunderland were probably still looking enviously at the money lavished on Gateshead's fantastically expensive Millennium Bridge. This was the back end of the millennial boom in iconic bridges, and the winner of Sunderland's design competition exhibited a compellingly flamboyant spirit (as did the designs from other entrants).

Now, in 2013, in a time of austerity, it may seem sensible to question not only the £82m of central government funding allocated to the project, but the £33m of Sunderland Council's own money, which I understood was to come by depleting the Council's financial reserves. Job creation may be cited in its defence, but the Wear Crossing will be nowhere near as effective at that as was, for example, Newcastle's Tyne Bridge, rushed onto site in 1925 largely for the direct employment its construction required.

As always, I'd be interested in readers' views on this subject, please click the Comments link on this post!

21 May 2013

Winner announced for Hamburg Southern Elbe crossing

A winner has been announced for the bridge design competition to design a new highway bridge across the Elbe near Hamburg. The bridge will connect the A1 and A7 highways, and is approximately 535m long, with a main span of 350m. The winning entry was selected from 12 competition entrants.

Winner: Schlaich Bergermann und Partner / Dissing + Weitling / WTM Engineers

Centrally located mono-tower cable-stay bridges seem to in fashion. The winning design in Hamburg is on a much smaller scale but bears a certain family resemblance to Hong Kong's Stonecutters Bridge, which is probably no surprise given the involvement of architects Dissing + Weitling in both designs.

Both bridges have twin planes of cables supported from two main towers (140m tall in Hamburg). These carry the inner edge of twin decks, which are connected ladder-like by a series of cross-girders. Both bridges have towers which flare below deck level and which are essentially prismatic for most of their above-deck height. This is a decision which is driven by the geometric requirements of the cable anchorages, to avoid unsightly cable attachments outside the tower envelope.

Below the lowest cable, the tower splits in two, with a similar twin-leg arrangement below deck, echoing the Millau Viaduct, another bridge which follows the mono-tower fashion. The same fashion has taken over in the UK, with Mersey Gateway and the Forth Replacement Crossing both taking the same approach. The reason, I believe, is visual legibility, with the single row of pylons and single plane of cables creating a far clearer silhouette than is achieved with more traditional twin-pylon and portal-frame pylon designs (UK examples include the Kessock Bridge, Second Severn Crossing and Dartford Crossing).

I don't know enough about these designs to comment on the economics - it seems to me that the greater torsional stiffness required in the deck for the mono-tower design, plus the much greater cross-section of the tower itself, will make it more expensive overall, even if the number of foundations and towers is reduced. The Southern Elbe crossing design is certainly reasonably elegant overall, although the second image shows how perspective can lead to a certain awkwardness when horizontal and vertical curvature is combined.

2nd place: Kinkel + Partner / Ges Consulting Engineers

The second placed design strikes me as quintessentially German, although the simple harp-type cable arrays here are those better known from Düsseldorf than from Hamburg. It always seems the most visually elegant arrangement, although rarely if ever the most economic, as the forces in both the deck and tower are greater than for the fan-type arrangement chosen by the winning entry. In the second-placed design, this is doubly true, given the wide spacing of the cables.

Indeed, it's hard to see how this bridge could be built economically. With a large number of cables, individual deck units can be relatively short, and hence straightforward to assemble in place as the bridge deck is progressively cantilevered out from the towers. Assuming the second-placed design has the same span as the winner, each deck segment is up to 40m long between cables, requiring both larger plant for erection and also potentially considerable temporary works to stabilise the main towers against out-of-balance bending.

3rd place: Ponting

Slovenian designers Ponting depart from the symmetrical two-span cable-stay solution with this asymmetric arrangement. Similar to the winning design, the main span is 355m, but with only one main tower, the masts have to be 200m tall to support the deck. It's not clear to me why such an arrangement would be preferred, and building inclined masts of such height requires some justification. I am not sure that the response of the cables to the deck curvature, or the desire to add transverse stability to what is already quite a wide deck, are sufficient.

There seems to be me an element of trying too hard to stand out, which is a frequent problem in bridge design competitions, and one which was also very much true in the Stonecutters Bridge contest some years ago. Ponting's website has several more images not shown here, plus a video.

16 May 2013

Foryd Harbour Bridge - an update

It's often the case that I report on interesting bridge projects but then never follow up on their progress. One such case is the Foryd Harbour Bridge, being built in Rhyl, in north Wales.

In June 2009 I reported the announcement of a winner in the Foryd Harbour bridge design competition, an unusual twin-bascule "drawbridge" type structure, designed by Gifford (now part of Ramboll) and to be built by Dawnus Construction. I also provided a few details of how the £4m design was proposed to work, including its low-maintenance GRP decks, and showed some of the unsuccessful design competition entries.

It took until March 2011 for the design to secure planning consent, and at the time it was stated that off-site fabrication would take place during 2011, with a site start in 2012.

Now the project seems to be making much better progress. According to the offical project website, the first of the two decks was delivered to site on 20th March 2013, with the second arriving just a few days ago, on 8th May. Delivery of the bridge mast is scheduled for 29th May, with the bridge decks craned into place at the beginning of June. I haven't seen any date announced for completing the bridge and opening to the public.

Isle of Wight based AM Structures, who fabricated the complex fibre-reinforced plastic decks, have a few images from the fabrication phase on their website. They make it immediately apparent that this is an exceptionally bold project, a real step forward in FRP bridge design and manufacture.

There are also some photos to be found on Facebook of the construction site, showing the bridge pier, abutment, and the first of the decks. However, for the best visual update on works, here's a YouTube video taken from a remote-controlled aerial camera, after the first deck unit had arrived on site.

14 May 2013

Katehaki Bridge, Athens

Late in 2012, I visited Athens, not a city generally noted for its bridges. However, I did get time to visit perhaps its most striking contemporary design, Santiago Calatrava's pedestrian bridge at Katehaki. This 94m long, 50m tall bridge was built in 2004 as an offshoot of Calatrava's other activities in Greece, designing the Athens Olympic stadium.

I had seen photos of the bridge beforehand, and like many of Calatrava's recent bridge designs, felt it was an example of a tendency to take things to extremes, unnecessarily so.

What makes this bridge seem so preposterous is the treatment of the cable-stay back span. In an asymmetric cable-stay bridge, where the main span is longer than the back-span, the back-span cables are generally anchored to the ground to provide the necessary stability. In most such bridges, the back-span cables are angled so that they provide a horizontal force, helping the bridge's mast to resist the horizontal pull from the main-span cables.

On the Katehaki Bridge, the back-span cables are instead vertical, resisting none of the sideways pull from the main span. Instead, that pull is resisted through the curvature of the pylon, as a compressive thrust. The curvature is a rational choice rather than simply a sculptural affectation - the pylon can be thought of as a uniformly loaded arch turned on its side, with the thrust at either end of the arch restrained either by the ground support or by the vertical back-span ties. The pylon is therefore essentially funicular in its form - its geometry responds directly to the forces applied to it.

As with many of Calatrava's bridges, the pylon form is well-sculpted, and the recessed cable anchorages are, in my view, visually a very successful detail. At its base, the pylon comes to a perfect point, with the weight of the entire bridge carried onto a support pedestal through a simple steel plate pivot, which cannot be more than an inch or two thick. The photo (right) shows this detail, and also shows the challenge to the bridge's fabricators of achieving Calatrava's continuous, curved forms - it's essentially impossible without fabrication tolerances making the welded plate joints more visible than would be desirable. The bridge was built by the Greek contractor Metka.

Katehaki Bridge was to be something of a prototype for Calatrava's much larger Puente de l'Assut de l'Or, in Valencia, a 180m long, 125m tall cable-stayed bridge of the same overall form. In both bridges, the pylon is offset to one side of the deck, an arrangement that Calatrava is inordinately fond of and which allows the sculptural nature of his structures to be expressed with great visual clarity. The penalty is that both pylon and deck are subject to significant lateral and torsional forces, adding considerably to the overall cost.

At Katehaki, the tendency of the deck to twist is addressed by building a steel box girder along one edge, incorporated into the parapet height so as to reduce its overall visual impact. The cable stay anchors are on the inside face of this box, which helps to counteract the tendency to twist.

The opposite edge of the deck supports an open post-and-rail parapet, an arrangement which can be used to strong visual effect where there is a desire to orient bridge users towards certain viewpoints. That doesn't seem to be the case here - it's simply an artefact of the prior design decisions.

The decking is formed in short timber planks, all lined up neatly rather than staggered. These are supported on steel ribs, and the whole deck is cross-braced to provide in-plane stiffness. The underside of the deck is given a somewhat scabby appearance by the deteriorating finish of the wood planks, although the top-side still looks very good.

There is some nice detailing at the end of the bridge away from the mast, where a triangular frame supports the bridge deck (I confess, I didn't take any note as to how the bridge may cope with thermal movement). The adjacent lift shaft and staircase structure has an attractive white terrazzo finish.

On the whole, the bridge does not feel out-of-scale to the task which it accomplishes, spanning a highway tunnel and two adjacent two-lane carriageways. It certainly makes crossing a busy traffic junction easier, as I found when having to cross other parts of the junction to take some of these photos.

Although the shape and height of the mast announces clearly the very conscious creation of a landmark (the bridge is unmissable on a car journey into the city centre from Athens airport), the more intimate features of the bridge have generally been detailed with care, and it's pleasant to walk across.

Perhaps the only thing that I find odd, and this is as a northern European visiting a southern European country, are the open-air escalators which provide access at both ends of the bridge. It's impossible to imagine such exposed machinery lasting long in a northern climate, although here they are simply an extension of the adjacent subway station, which is also entered via exposed escalators.

Overall, I very much enjoyed visiting this bridge, it strikes me as a very successful design (at least visually - it cannot have been particularly cost-effective).

Further information:

07 May 2013

Bridges news roundup

Wow, has it really been over a month since I last posted? Life remains very busy, so even putting together a simple blog post on a bridge I visited six months ago is proving difficult. Until that happens, here are a few news items:

A Wavy, LEGO-Inspired Concept For A Public Footbridge
"Those who use the Footstep Bridge, experience a new way of crossing over a road, river, etc." Yes, a really tedious, annoying way.

The tabikappa blog has, as always, several rather excellent Japanese footbridges to showcase, of which my favourites are one, two, and three.

IABSE Workshop: Guidelines for Design Competitions for Bridges
The international guidelines receive a UK launch at the IStructE on 21st June. The Happy Pontist plans to be there and will report here afterwards.

New Bridge in Gothenburg, Sweden
Only just over a week to go for anyone wanting to prequalify for this highway bridge design competition. You can download information from the official competition web page.

Sneak peek at new footbridge proposals
Images of a proposed swing footbridge at Deptford Creek, London.

Sculptural London lift bridge secures planning permission
Very unusual bascule footbridge at Paddington, London (pictured), takes a step closer to becoming reality.

Boston bridge will benefit whole of Lincolnshire
A somewhat bold claim for a little footbridge, due to be built this summer.

YouTube has three short films about Copenhagen's Inderhavnsbroen, the "kissing bridge" currently under construction, interviewing designers Ian Firth and Cezary Bednarski. Onetwo and three.