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Polcevera Lessons

Pa 38027956 (1)

I read your Comment on the Polcevera viaduct collapse and agree with the general sentiments expressed regarding inspection and maintenance (New Civil Engineer, September 2018). Main cable corrosion in UK suspension bridges was first detected in the cables at Forth Road Bridge during my time as chief engineer and Bridgemaster. The investigation at Forth was carried out in 2004/05 by Aecom and Weidlinger and, following the discovery of corrosion in the cables, the owners and operators of Humber and Severn were invited up to Forth to see the extent of the problem and, afterwards, made arrangements to open up and inspect their cables.

At the time of opening up the cables at Forth there were some dissenting voices concerning the need to do so. However, we felt that it was not possible to carry out a “principal inspection” of one of the most critical elements of the bridge without opening the cables up to inspect the bridge wires. We were also acutely aware of the problems experienced on several US bridges.

Without that early intervention, it is likely that the deterioration of the cables on Forth, Severn and Humber would have continued undetected and the decision taken by all three owners to install a system of cable dehumidification, and thus stabilise the loss of strength, may not have been made in time to prevent more serious damage occurring.

  • Barry Colford,

Although the viaduct has been praised for its unusual and innovative design, therein lies the rub. Where novel and unusual design features are present there will be little in-service experience of structural resilience under the deleterious effects of, for example, fatigue, corrosion and often increased loading over the operational life.

Therefore specific engineering scrutiny is essential to assess the structure’s vulnerability to failure modes to specify an inspection and surveillance plan which focuses on the unusual (and critical) components. This data, regularly updated, identifies deterioration rates and informs the integrity status benchmarked to documented performance standards.

This should, of course, be instigated at the start of service life and subject to regular formal review throughout the life cycle as part of the overarching structural integrity management strategy.

  • Terry Rhodes (M)

The chilling report by Katherine Smale from the silent sunshine at the site of the awful bridge tragedy at Genoa must have made all engineers reading it think of the mistakes that we too, in all of our careers have made, and perhaps it is time now to stop worrying about “raising the profile of our profession”.

Civil engineering facilitates things; it does not orchestrate them. It is probably more worthwhile to concentrate on what is actually built on site.

  • Dennis Gedge (M) Newton Poppleford, Devon

Your Comment fails to mention the Medway Bridge which was opened in 1963. It presented the world’s longest prestressed concrete span at the time of 152.4m. It is not cable-stayed and its articulation creates a statically determinate structure. After more than 50 years’ service it is in excellent condition and was recently upgraded to take additional traffic lanes through additional post-tensioning and replacement of the concrete suspended span with a lighter steel structure. The original specification called for a foundation system to stand for 200 years.

  • Geoff Thornton (M)

Between each of the cable-stayed spans there was a short suspended span which appears to be half jointed. There was a similar short suspended span between the collapsed cable stayed span and the approach viaduct. In the video across the rooftop (in heavy rain) that shows the mast collapsing it appears that this suspended span had already dropped before the mast collapsed. It could have been a half joint failure that initiated a progressive collapse.

  • Nick Thoday Posted online on article headed “Exclusive | Collapsed Italy Bridge investigators find corrosion on main stay cables”

It now seems quite possible that the principal reason behind this catastrophic failure was the designer’s decision, 50 years ago, to use steel tie bars clad in concrete as the bridge’s main tension members. This was essentially a cable stayed bridge design in which the steel tension cables were wrapped in concrete instead of paint (or a similar corrosion resisting medium). The concrete wrapping provided no structural benefit to the bridge and instead went on to prevent the ready inspection and maintenance of the main steel strength members it enclosed.

Concrete is excellent for compressive loads but useless in tension. Steel is excellent for tensile and compressive loads but needs a protective coating to prevent corrosion.

Also it seems that there was also no redundancy in the structure – a single member failure could lead to total collapse.

 These are significant design failings in my view.

  • Ronald Drysdale, Posted online on article headed “Exclusive | Collapsed Italy Bridge investigators find corrosion on main stay cables”

Editor’s note: Read more comments here

We need clarity and accuracy about governance vote

I was surprised and disappointed to see the inaccurate reporting of the Special General Meeting (SGM) and the governance vote in September’s New Civil Engineer.

To report the SGM was held after the ballot earlier that month “in which more than 70% of corporate members voted in favour of bylaw changes…” is incorrect.

It is an example of the misleading and inaccurate statements made at the SGM and, in part, why the result of the SGM expressed its disappointment at the conduct of the matter by the President and Council.

The fact is that 6.3% of corporate members voted in favour of the bylaw changes.

That may be 70% of those who voted in the ballot but it is not 70% of corporate members. There were other similar intentionally misleading statements made at the SGM.

The concern of members who made the effort to attend the SGM is for a fair and open process with good consultation and for the outcome to be representative of the views of the Members. I trust the Council will have proper regard for the views of members when it reconvenes.

  • Howard Hughes (M)

Editor’s note: We have received several letters echoing Howard’s point. We thought it was clearly inferred that by saying 70% of the membership we meant 70% of the membership that voted, and it was certainly not our attempt to mislead. ICE president Lord Mair writes on p22 of this issue further explaining the ICE’s position and approach.

What is the truth behind sea level rise claims?

In the article “Losing to Win” Greg Guthrie of Royal HaskoningDHV notes that the national average sea level rise is approximately 4mm a year (New Civil Engineer, last month). He then continues “There is strong evidence that climate change is happening in line with the current projections, which could see 1m rise over the next 100 years.” In the next article “Defence by Design”, the subsection on London states that the flood risk management work is based on a relative sea level rise of 900mm by 2100 and is adaptable to 2.7m by 2100.

The facts for East Anglia, one of the highest relative sea level rise (SLR) areas in Europe, are:

  • Isostatic land subsidence is 1.47mm/year
  • UK mean (absolute) SLR is 1.4mm/year
  • Tidal range increase is 0.6mm/year
  • The sum of these gives the mean high water springs sea level rise value of 3.47mm/year.

I find it difficult to conceive of the changes within the time scale that the New Civil Engineer articles are intimating. We are asked to believe that the UK rate of mean sea level rise will increase over the next 82 years to 20mm/year for a 900mm rise and 64mm/year for a 2.7m rise (linear acceleration) – more than four times the rate of the last deglaciation.

Why is the range of prediction so large? What measured evidence is there to predict these levels of increase? One wonders if there is not a hidden agenda based on political views, and hard evidence is being sidelined for commercial gain. 

  • Robin Whittle (M)

Crossrail Civils work let down by M&E complexities  

I wonder if there is not a bigger lesson to learn for civil engineers. The complexities of some of the mechanical and electrical (M&E) systems required today may leave project managers with a civil engineering background floundering to understand the intricacies of M&E installation and testing packages.

04 crossrail western tunnels 35507

04 crossrail western tunnels 35507

Engineers need more M&E knowledge

They are possibly lacking in sufficient knowledge to challenge when things go wrong, and more importantly, do not take seriously that seemingly enormous amount of time M&E engineers initially want for testing, and which the civils team can so easily view as its own float if things don’t go quite right.

Of course there is a political downside for allowing long periods for testing. The project looks complete and as far as the public and politicians are concerned it should be open.

  • Paul Arnold posted online on article headed “Crossrail confirms delay of up to a year for Central London section”

Interchanges: Balancing stakeholder demands

I have just retired as head of stations for WSP and have led design teams on many of the station projects mentioned in Jackie Whitelaw’s article in the August edition. I concur that there are exciting and challenging times ahead of us in the design and construction of our future transport hubs.

However, these interchanges are expensive and involve many stakeholders, whose aspirations are invariably unaffordable, particularly if funded from the public purse.

Attracting private investment is therefore critical, but the need to maximise property value from over and adjacent site development needs to be balanced with the need for transforming these interchanges into functional but aesthetically, sustainable and environmentally friendly places.

Hs2 southern entrance

Hs2 southern entrance

The Euston High Speed 2 masterplan had to reconcile private developers’ demands with design and energy considerations

We must give the stakeholders the opportunity to voice their views through extensive consultation but not go back for a second or third bite of the apple once agreements have been reached and, hopefully, an acceptable masterplan for development has been accepted.

The challenge the WSP/Wilkinson Eyre team had in producing such a masterplan for Euston station for High Speed 2 was balancing the aspirations for oversite and adjacent site development with natural light to the station and sufficient roof space for renewable energy (photovoltaic cells).

I consider we achieved this and while I do not expect the masterplan to be strictly adhered to it provides a framework for the Master Development Partner to work to in maximising property value capture while not compromising the station environment.

Promises which are unaffordable must not be made to stakeholders including the government; it is our role as professionals to ensure that our clients and those who are funding these mega-projects are advised accurately at the start and throughout project development of what can and cannot be achieved within the constraints of budgetary, environmental, operational and, not least, safety requirements.

  • Dave Darnell (M)

Finding the answer from Florida

Reading of the Florida bridge “experts”’ approval of 25mm+ wide cracks just three hours before the fatal collapse defies belief (The Edit, last month), and demands more answers that New Civil Engineer must chase. Please tell us that over five months later, these civil engineering “experts” are at least no longer in positions to make such judgements.

I am a retired civil engineer conducting voluntary monthly visual checks on a 165 year old seven arch masonry viaduct we are hoping to reopen to the public as a heritage railway next year, but even I am aware of the responsibility this gives me to the travelling public, and as a bare minimum, the inability to sleep it would cause me if it collapsed on my watch.  

If our trade journal can’t even hold our colleagues to account, what hope is there for the public reputation of our profession, let alone find justice for the six we killed in Florida and the 43 in Genoa?

  • Tom Lloyd (M)

Engineers must consider the big picture

As usual, you have some good letters in your latest edition (Your View, August 2018). Perhaps Professor Blockley’s sums them all up. What he describes as “systems-thinking” or “joined-up thinking” is no more than what I have always regarded as good engineering.

If you aren’t looking at the bigger picture (John Tuson’s point, perhaps?), the social and cultural context (Martin Knight’s?), and thinking about the construction, not just some ‘wished-in-place’ wonder (Mike Franklin’s?), then you are not an engineer. You may have a valuable role to play, contributing to engineering work. But for an engineer, it is this bigger thinking that matters most.

The details of analysis and conforming to rules (which may be past their use-by date), will always be secondary, no matter how important their roles.

  • Paul McCombie, admissions tutor for civil engineering, Department of Architecture & Civil Engineering, University of Bath




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