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Letters: Anatomy of failure at Hammersmith Flyover

Hammersmith_A_6208a_1_

I have been reading with great interest about the Hammersmith Flyover in recent weeks and pondered Transport for London’s decision to initially close the bridge completely but not the roads beneath.

One can only conclude that the bridge is not in imminent danger of collapse.

It appears that the post-tensioned tendons are corroded most severely over the piers, where they are installed to prevent tension cracking in the top slab of the box girder under hogging moments.

A loss of prestress here would result in serious cracking but not necessarily catastrophic failure. The tendons at segment midspan in the bottom flanges of the box must be anchored at separate blisters from those over the piers.

It would appear from reports that these tendons have not corroded, which is fortunate as I imagine a loss of prestress at midspan to be far more serious.

Depending on the amount of prestress loss over the piers, the box girder may already have cracked locally under live load.

It is likely that a considerable proportion of the prestress over the piers remains despite the corrosion, and therefore designing new tendons while assuming this force does not exist may actually result in too much compression in a section of concrete already weakened by cracking.

The moratorium on post-tensioned segmental bridge construction using grouted internal ducts was enforced due to concerns over the durability and detailing at the joints. After the installation of the remedial external prestressing at the Hammersmith Flyover, it will be interesting to note what preventative action is taken for the remaining segment joints to avoid a reccurrence of the same problem.

  • M Myerscough, 12 Lower Church, Street, Chepstow, Monmouthshire NP16 5HJ


20th century engineers

I see that nominations are being sought for inclusion in a list of 60 New Elizabethans, one for each year of the Queen’s reign.

While I can readily identify a number of eminent Victorian civil engineers I am having difficulty in thinking of any outstanding English civil engineers from the past 60 years.

If there are any, whom should we nominate?

  • Harry Valentine, 32 Inglewood Crescent, Hairmyres, East Kilbride G75 8QD


Water meter argument is biased to the South

I sincerely hope that the statement in NCE (News last week) that “Water metering must be introduced across the UK if the spectre of annual droughts is to be avoided, the ICE has warned,” is a mistake.


There has been an extremely dry winter in the South East, but in the north west of England, in Northern Ireland and Scotland there has been more than enough rainfall - well above average in fact.

Having been involved in water policy development for many years, I might go on to point out that the problems in the South East are endemic and ancient. Forty years ago the Heath Government failed to grasp this nettle in the Water Act 1973.

At that time it failed to give the new regional water authorities sufficient power to compel the integration of water supply and resources in their area. This entrenched the severe problems in the area of Southern Water, with its several independent water companies - coincidentally in the driest corner of UK with some of the highest per capita incomes, rates of growth and rapid development.

Privatisation and its concomitant economist’s dream of competition between the fragmented companies has compounded the problem.

People to the north and west of the Home Counties must be groaning once again at the total dominance of UK by London, the Home Counties and the South East.

  • John Thackray (F), je.thackray@ntlworld.com


Estuary airport or expanded Birmingham?

The prospect of Birmingham Airport being expanded to increase UK runway capacity must be anathema to many thousands of residents of London and Birmingham(NCE 9/16 February).

To have another large conurbation then subject to the continuing and continuous aircraft noise pollution must surely be a major retrograde step.

The Thames Estuary location with its substantially increased capacity means it is likely British Airways would move there lock, stock and barrel, like it did when it relocated to Heathrow Airport’s Terminal 5 when it opened.

This would virtually reduce Heathrow to a non-hub function, obviating the need for interlinking between there and the estuary, as well as substantially reducing the macro-noise problem at present at Heathrow.

Also who is going to guarantee that High Speed 2 will be built, and when, for Birmingham to be a sound investment solution? The High Speed 1 facility is already in existence nearby for the estuary location.

Finally, as regards accessibility to workers and passengers, other worldwide coastal solutions, Hong Kong, Japan, et al, do not appear to suffer a problem with their locations from that aspect. East London is as good as West London for this aspect.

  • John Franklin (F), 11 The Ridings, East Horlsey, Surrey, KT24 5BN


HS2: get Prince Charles involved

While Prince Charles was visiting One Great George Street it would have been a good time to ask his views on the present High Speed 2 proposals.

Environmentally friendly sustainable development - I think not.

The whole project should be built following the line of existing motorways but completely in tunnel, thus saving future generations the inevitable noise, visual intrusion, weather delays and the considerable ongoing costs associated with future landscaping and surface maintenance.

  • Peter Hardy (M), peter@hardy.uk.net


Let’s get serious about climate change

I was disappointed to see a picture of a fortune teller above a letter about climate change, especially in the issue where Prince Charles urges the Institution to take climate change seriously (NCE 9/16 February).

The picture backs up the frivolous nature of the letter and the caption appears to endorse the content.

The large changes that we are making to greenhouse gases in the atmosphere will have a profound effect on our climate. Greenhouse gases trap heat in the atmosphere and it is difficult to see how a doubling or even trebling of carbon dioxide would not have a large effect.

Whatever the accuracy of climate models we cannot escape this fact. Climate projections are the best information that we have to help plan for the future. Although modelling is difficult and imperfect, it is better than burying our heads in the sand and just hoping for the best.

A range of factors influence warming and the scientists do what I, as a structural engineer, would term a sensitivity analysis of the complex interactions. Climate change deniers use the scientific rigour of the researchers to imply that the science is flawed “and indicates a lack of faith in their own figures” (NCE 9-16 February).

To see how science has been distorted over the years, read Merchants of Doubt by Oreskes and Conway. This shows special interest groups have misled governments, and the public, from tobacco not causing cancer to climate change being a liberal conspiracy.

  • Adrian Pope (M), AKPope@btinternet.com

Abingdon goes back on the agenda

abingdon

Surely the present drought situation throws into doubt the decision not to go ahead with Thames Water’s Abingdon Reservoir.

This was one of the most short-sighted decisions in public water supply for decades.

Not only would it capture winter runoff in the River Thames to reinforce supplies into the London area, it could be used to relieve the environmentally damaging low-flows in the River Kennet by allowing the closure of the pumping station at Axford which starves the river of water at its top end.

  • Rodney Bray (M), Newbury, rodneycbray@googlemail.com

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