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Your View | Usk bridge design flaws

River usk deck night view 1 crop

In my capacity as chief bridge engineer for the Welsh Assembly Government I had significant involvement with the inspection and assessment of the structural integrity of the Usk Bridge hinge deck joints and make the following observations on your feature and Richard Williams’ subsequent letter defending the structure’s original design and construction (New Civil Engineer, September).

With regard to the “design faults”, I do question the wisdom of incorporating stability-critical components (the horizontal hinge joints) into a structure when there is no secondary means of support, where it is impossible to non-destructively inspect and where the consequence of their failure is progressive collapse of the whole structure.

As in all reinforced concrete, the reinforcement in these joints is vulnerable to corrosion due to the effects of de-icing salts. Protection is provided by the bridge deck waterproofing and a joint-filler that is subject to compression and stretching with every traffic- induced rotation of the hinge joints. With regard to the “constructed incorrectly” statement, there certainly were construction faults.

If I remember correctly there was localised bridging of the lower slots in the hinges of some of the main deck beams due to concrete overspill and complete omission of the slot detail to lengths of the transverse diaphragms between beams.

These construction faults meant that the diaphragms could not properly perform their function in unison with the rotation of the main beams and compromised the rotational behaviour of the joints; there was extensive cracking in the diaphragms and delamination of the beam soffit concrete as a result.

While the article appears to focus upon issues surrounding vulnerabilities of the hinge at its periphery due to deterioration, I recall that laboratory testing of a representative model of the joint using highly sophisticated finite element analysis and fatigue testing showed that the joints have limited remaining fatigue life. The real complex behaviour of the joints is not the pure rotation envisaged by the designer. It is true to say that there are shortcomings in the design of the thrust-hinge.

In summary, the main lesson to be learnt from this experience is that structures should never incorporate stability-critical elements that cannot be inspected, replaced or strengthened.

  • Thomas John Collins (M Retd), johncollins@groesfaen.plus.com

Congratulations to Richard Williams in his defence of his grandfather’s use of reinforced concrete hinges in bridge decks. Having begun my career in civil engineering in the days before both computers and road salts as a fourth generation member in the construction industry,  I’ve experienced privileged involvement in physical model research in several of Sir Owen’s neat solutions, including circular pile caps, crossbeams with panel walls and deck hinges. Each was found to be most effective and, once unexpected issues arising from road salts were addressed, almost all elements were able to continue in use.

In the 200th year of our Institution, it is worth understanding how such a solution for one era may have pitfalls within the next, but that need engender no disrespect for our forebears.

  • Iain Kennedy Reid (M Retd), kennedyreid@btinternet.com 

 

Basic Carlisle station roof risks missed

Reading your report on Carlisle Station roof refurbishment proved to be interesting. But it seems that it misses the most important point and, to be honest, may be misplaced as a Tech Excellence report. True, the construction procedure is noteworthy.

But missing the risk of uplift being a constraint during the design stage is extremely troublesome. This is engineering basics and should never have happened.

Aiming for high tech solutions and missing the basics should not be presented as good engineering. Only vanity.

  • Jorge Rocha (M), jrocha.eng@gmail.com

 

Hyperloop’s technical challenges

When is someone going to challenge the geometric nonsense and journey time daydreaming being espoused by Hyperloop?

  • A 3km horizontal radius at 800km/h.  Please explain the sideways forces involved and the applied cant/superelevation.
  • Please explain the vertical curvatures involved. How is the topography followed?
  • Please explain how the graphic of a tube on stilts alongside a motorway works at side road over bridges.
  • What acceleration and deceleration rates of g, and top speeds, are needed to achieve the stunning journey times claimed?
  • How does the “deceleration lane” off the main tube work? On High Speed 2 for example, the diverging line departs from the through line about 2km from the station so that a stopping train doesn’t impede the following non-stop train. Now explain that at 800kph.l How are passengers supplied with air in the “pod” while travelling in a near-vacuum?
  • What are the arrangements to retrieve a pod’s passengers in case of a pod stopped in mid-tube? And how are passengers in the following, also stopped, pods reached?

There are far too many questions to be answered and your readers will doubtless have many other concerns about this technical naïvety. Getting a pod to travel along a tube in a developmental stage is the easy bit.

  • Phil Hall, 11 Fernhill Drive, Leamington Spa

Queensferry Bridge: Not made in the UK

In your report on the newly-opened Queensferry Crossing (New Civil Engineer, October), you claim that “the materials spend is split between Scotland and overseas” and that “most orders for the bridge have been placed with Scottish suppliers and subcontractors”.

As someone who has been watching the construction of the bridge for the last few years I fail to see how this can be claimed.

Not only were the steel deck sections fabricated in China but so were the big steel cable boxes in the towers as well as the bridge’s two giant expansion joints.

Queensferry bridge with tartan (1) crop

Queensferry bridge with tartan (1) crop

Queensferry: Not a very British project

The three sub-sea steel caissons were manufactured in Poland and the sheet-steel piles for the cofferdams came from Spain.

The miles of high-tensile steel cables which hold the bridge up were produced in Switzerland with steel from Austria and Italy. When I asked Transport Scotland where the thousands of tonnes of rebar were sourced I was told “from all over”. The only major structural components that hailed from Britain seem to have been the two box-girders for the south side viaduct which were manufactured by Cleveland Bridge.

You also failed to mention how the Forth Crossing Bridge Contractors consortium was divvied up. The three foreign firms, American Bridge, Dragados and Hochtief, took 28% each of the contract while Morrison Construction (the Scottish arm of Galliford Try) took only 16%. Oh, and the contracts for the approach roads were let to firms from Ireland (the Republic and the North).

I defer to no-one in my admiration for the quality of the design and engineering of the bridge. It really is a beautiful structure.

But I find the lack of British-made and British-supplied components very disturbing. And it raises questions: are we capable of building structures like the Queensferry Crossing ourselves? Or are we destined to rely more and more on the expertise of other nations for our engineering?

  • George Rosie, Edinburgh, georgerosie2@blueyonder.co.uk

Spreading the word

Most organisations recognise and value the professional status of their employees. They have specified criteria for promotion of their employees to senior positions. Their employees are elevated to responsible positions after gaining professional qualifications.

At the same time, one can come across so many examples within the engineering community where professionally unqualified persons are working on key technical and in managerial positions and keep on moving up the ladder at regular intervals. I do not doubt their competence and potential, but sticking to the rules of the game and application of consistent criteria across the engineering organisations is important.

Young engineers cannot be motivated to become professionally qualified, if such instances are noticed by them frequently. If the trend continues, the merit-based promotions will get a blow and culture of personal relationship and sycophancy will get encouragement. The ICE needs to play its due role on this issue. The prestige of the Institution and gold standard of engineering should be kept intact at all cost.

  • Muhammad Bhatti (F), bhatti84@hotmail.com

Daytime streetlighting: A Waste of energy

Recently while driving along the A2 towards London, I said to my companions that on any day in the last 10 years they could have counted at least 20 lights burning in broad daylight between the M25 and A223 junctions, a distance of about 6km. They treated this remark as somewhat whimsical but of course they counted; 21 was the score. Today in sunshine the total was 30.

Modern management approach would presumably have highway lighting controlled under a commercial contract. If this is so, elimination of this continuous energy waste should be easily achieved merely by applying sufficiently high financial penalties. Why is this not done?

  • KG Bowman (M, )kandmbowman6@gmail.com

 

 

 

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