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.


Brian Potter, PE said...

Interesting to contrast this with the recent furor over fracture-critical bridges (ie: bridges with non-redundant tensile members) in the US, spurred by a recent collapse: http://seattletimes.com/html/localnews/2021045926_bridgecollapsexml.html

Anonymous said...

Hi HP, Simon Bourne should be commended for speaking out on the project. Everything he said was correct and well thought out.

Thanks for posting his article!


The Happy Pontist said...

Some very good further comment on this over at Tallbridgeguy: "This got me to thinking about how engineers are perceived as the party of No."

Anonymous said...

I wholeheartedly applaud Simon Bourne for sticking his neck above the parapet. It does make you wonder though how we engineers have arrived at this position, and whether we are corporately partly to blame? Why is it that engineers nowadays always seem play second fiddle to architects? Why aren’t more leading bridge professionals prepared to speak out? Surely it is partly because we are too timid and shy to make our voices heard?

If Simon is the only bloke out there with the guts to point out the *@?$*! obvious, then he should be supported and encouraged to take his message to the highest level possible. The figures we are talking about are breathtakingly huge, and if he can persuade the decision makers to change their mind, he should be knighted for services to his country! The balance of power from engineer to architect in the bridge world has swung much too far in one direction – creating ludicrous situations now such as River Wear.

Love the analogy of a one winged plane – brilliant, and appropriate!