Hammersmith Flyover 'Is Unsafe'

This sounds dramatic!

A whistleblower claims that the Hammersmith Flyover is in a dangerous state due to corroded cables. The regular inspections apparently didn't uncover any dangerous defects but now it's been brought to the attention of the public suddenly £10 million is being spent on renewing broken and corroded cables.

londonist.com...

The continuation of the story.

londonist.com... serious-defect.php

Here are a selection of views on the subject.

www.disco3.co.uk...

And here, perhaps most telling of all and an indication of greater problems with this method of construction. From the randompottins blogspot.

"I'm no enginer, but it sounds to me like the bridge is actually built employing the technique of post-stressed concrete, whereby cables are tightened within the concrete after it is laid. Back in the early 1970s I was sharing a house up North with a couple of friends, one of whom was employed as a technician on motorway construction. One day Steve came home not his usual carefree self, and told us that he had been testing the grout, a mixture of cement and sand in water, that was used to surround cables embedded in concrete, in order to seal them from the elements. Finding a batch that was not of the proper consistency - I think it was meant to be cement-rich - he had reported this, only to be told to let it go.

Steve explained that if the cables were not properly grouted and sealed, rainwater permeating through the concrete would cause them to rust, and you might eventually have lumps of loosened masonry from bridges falling down on to the motorway.

I told him somewhat naievely that he ought to go to the press with his story. He replied that if he did that "it would be the end of my career in civil engineering and construction". He was probably right. He won't mind me telling his story now, as last thing I heard he had gone into teaching instead."

It all sounds a bit familiar.

www.abovetopsecret.com...

The Hammersmith Flyover was originally constructed to have hot water/ steam pipes embedded within it, the idea being that during cold weather the hot water / steam would run throught the pipes and stop the road surface from icing up, new technology back then. Problem was it never worked, so years and years of laying salt down during these times and the water run off running into unsealed cable holes has created the corrosion problem. If the original system had worked we wouldn't be in the situation we are now.

reply to post by FFS4000


Thanks for the input.

This is the situation with prestressed concrete structures the world over. The Transportation Research Board (TRB) is a division of the National Research Council, which serves as an independent adviser to the President, the Congress and federal agencies on scientific and technical questions of national importance. This is their view on the subject. ".....corroded strands may go undetected and result in catastrophic failure... Further; it is now known that corrosion issues may exist in both reinforced concrete and prestressed concrete bridges."
"There is an urgent need to develop reliable and inexpensive techniques to assess the internal prestressing components. The corrosion of prestressing tendons and an inability to assess their condition has led to a number of structural failures in the recent past...."
"Most of the recent structural failures on the list did not exhibit signs of distress prior to collapse. Internal voids were identified in the Varina-Enon Bridge through routine inspections and these voids were filled with good quality grout. It was assumed that completely filling the voids would stop further corrosion from occurring. However, corrosion increased even after the voids were completely filled with grout. It appears that corrosion and potential failure of post tensioned structures is more problematic than previously thought.

A typical investigation of the corrosion of prestressing tendons maybe performed by visual inspection augmented with the use of a bore scope, use of impact echo testing, an evaluation of corrosion potentials, and an assessment of chloride contamination. It is now known that this approach has not always identified ongoing corrosion and has actually provided a false sense of security while tendons continue to corrode.


It has also been verified that tendons can corrode even when completely covered by grout. Within voids and despite low pH grouts, corrosion has occurred irrespective of low chloride concentration. At times, the rate of strand corrosion may increase when voids are filled with fresh grout. The cause of this phenomenon is not fully understood and requires study."