http://www.bbc.co.uk/news/uk-england-london-16540112

Boris Johnson, mayor of London, has announced that the Hammersmith
Flyover in west London, which has been closed for three weeks, will
reopen on Friday.

It was shut when serious damage to cables in the structure was
discovered.

Transport for London (TfL) has said one lane will be open in each
direction but it will be closed to HGVs and coaches.

Closure of the A4 route, which is usually used by about 90,000
vehicles a day, has caused serious congestion in west London.

'Reduce disruption'
A steady seepage of salt water into the structure, built in the 1960s,
has weakened the structure, but engineers said it was now safe to take
light traffic.

TfL said the route would reopen "before the rush hour" on Friday but
did not specify exactly when.

Strengthening work will continue for the next four months and drivers
are still advised to "consider avoiding the area if possible".

Once new cables are installed, the flyover will be reopened to all
traffic "well ahead of the London 2012 Games", said TfL.

Garrett Emmerson, chief operating officer for surface transport, said:
"This should significantly reduce the traffic disruption many
thousands of drivers have been experiencing since the flyover closed."

http://www.bbc.co.uk/news/uk-england-london-16540112

Bruce wrote:
A steady seepage of salt water into the structure, built in the 1960s,
has weakened the structure, but engineers said it was now safe to take
light traffic.


The flyover was equipped with electric heating elements under the road
surface. These were specified in order to eliminate damage to the
pre-stressed concrete structure from de-icing salt.

Apparently the heating elements never worked properly from the outset.
In that case, the best alternative would have been to use urea for
de-icing, as is routine practice in Germany and some other countries.
But no, the cheaper but potentially very damaging rock salt was used,
and this is what has caused the problems with the pre-stressing cables
within the concrete structure.

"Bruce" wrote in message
...
Bruce wrote:
A steady seepage of salt water into the structure, built in the 1960s,
has weakened the structure, but engineers said it was now safe to take
light traffic.

But no, the cheaper but potentially very damaging rock salt was used,
and this is what has caused the problems with the pre-stressing cables
within the concrete structure.

Presumably this isn't the only structure of this type on the road network
though?

Are many more due to be found before long?

Paul S

"Paul Scott" wrote in message
...
"Bruce" wrote in message
...
Bruce wrote:
A steady seepage of salt water into the structure, built in the 1960s,
has weakened the structure, but engineers said it was now safe to take
light traffic.

But no, the cheaper but potentially very damaging rock salt was used,
and this is what has caused the problems with the pre-stressing cables
within the concrete structure.

Presumably this isn't the only structure of this type on the road network
though?

Are many more due to be found before long?

Found to have damage, I meant of course. Not just 'found'!

Paul S

In message , at 12:41:12 on
Fri, 13 Jan 2012, Paul Scott remarked:
A steady seepage of salt water into the structure, built in the 1960s,
has weakened the structure, but engineers said it was now safe to take
light traffic.

But no, the cheaper but potentially very damaging rock salt was used,
and this is what has caused the problems with the pre-stressing cables
within the concrete structure.

Presumably this isn't the only structure of this type on the road
network though?

Are many more due to be found before long?

There were extensive repairs to the M6 viaduct in the Castle Bromwich
area a couple of years ago, and the A14 flyover across Huntingdon
station is widely regarded as being about to fall down. One of the
bridges at the M6/M1 junction was replaced very recently.

http://www.bbc.co.uk/news/uk-england-16460505

Not sure how many of these are salt related.
--
Roland Perry

In article ,
(Bruce) wrote:

Bruce wrote:
A steady seepage of salt water into the structure, built in the 1960s,
has weakened the structure, but engineers said it was now safe to take
light traffic.

The flyover was equipped with electric heating elements under the road
surface. These were specified in order to eliminate damage to the
pre-stressed concrete structure from de-icing salt.

Apparently the heating elements never worked properly from the outset.
In that case, the best alternative would have been to use urea for
de-icing, as is routine practice in Germany and some other countries.
But no, the cheaper but potentially very damaging rock salt was used,
and this is what has caused the problems with the pre-stressing cables
within the concrete structure.

Unless there was a general switch to urea over a wide area around the
flyover there would inevitably have been large amounts of salt carried onto
it since it opened anyway, surely?

--
Colin Rosenstiel

"Paul Scott" wrote:

"Bruce" wrote in message
.. .
Bruce wrote:
A steady seepage of salt water into the structure, built in the 1960s,
has weakened the structure, but engineers said it was now safe to take
light traffic.

But no, the cheaper but potentially very damaging rock salt was used,
and this is what has caused the problems with the pre-stressing cables
within the concrete structure.

Presumably this isn't the only structure of this type on the road network
though?

Are many more due to be found before long?


There are plenty of structures of this type (precast segmental
pre-stressed post-tensioned) but I think the Hammersmith flyover was
the first. I don't know of any subsequent structure of this type that
lacks the essential combination of bridge deck waterproofing, proper
drainage, adequate concrete cover to reinforcement/pre-stressing
tendons and grouting of tendon ducts.

So Hammersmith is very much a one-off. That doesn't mean that other
structures don't have problems of their own, but the design and
subsequent operation and maintenance practice related to the
Hammersmith flyover seems to have combined in a way that could only
end in tears.

"Bruce" wrote in message
...

There are plenty of structures of this type (precast segmental
pre-stressed post-tensioned) but I think the Hammersmith flyover was
the first. I don't know of any subsequent structure of this type that
lacks the essential combination of bridge deck waterproofing, proper
drainage, adequate concrete cover to reinforcement/pre-stressing
tendons and grouting of tendon ducts.

So Hammersmith is very much a one-off. That doesn't mean that other
structures don't have problems of their own, but the design and
subsequent operation and maintenance practice related to the
Hammersmith flyover seems to have combined in a way that could only
end in tears.

I bet the DfT (or the Highways Agency) are glad that they they ceded all
the trunk roads within London to the GLA. I'm thinking it must have been
transferred at about the same time that all those random motorways within
London were downgraded?

Paul S

"Paul Scott" wrote:

"Bruce" wrote:

There are plenty of structures of this type (precast segmental
pre-stressed post-tensioned) but I think the Hammersmith flyover was
the first. I don't know of any subsequent structure of this type that
lacks the essential combination of bridge deck waterproofing, proper
drainage, adequate concrete cover to reinforcement/pre-stressing
tendons and grouting of tendon ducts.

So Hammersmith is very much a one-off. That doesn't mean that other
structures don't have problems of their own, but the design and
subsequent operation and maintenance practice related to the
Hammersmith flyover seems to have combined in a way that could only
end in tears.

I bet the DfT (or the Highways Agency) are glad that they they ceded all
the trunk roads within London to the GLA. I'm thinking it must have been
transferred at about the same time that all those random motorways within
London were downgraded?

Yes, when the GLA (and hence TfL) was established in 2000. It formed part of
what was initially called the GLRN (Greater London Road Network),
subsequently renamed the TLRN (Transport for London Road Network).

I doubt it, but it could conceivably have been a responsibility of H&F
council pre-2000, rather than that of the HA. I think it fell under the
auspices of the GLC in years past. Be interesting to know when the
quasi-literal rot started!

Re the downgraded motorways - I've read elsewhere speculation, which seems
to have turned into received wisdom amongst some, that this only happened
because of an oversight with the legislation establishing the powers of the
GLA. I have my doubts about that theory - rather, I can well imagine it
being intentional (the thinking being that the notion of widespread 'urban
motorways' is rather something of the past) - but that's just speculation on
my part.

"Mizter T" wrote:
"Paul Scott" wrote:
"Bruce" wrote:
There are plenty of structures of this type (precast segmental
pre-stressed post-tensioned) but I think the Hammersmith flyover was
the first. I don't know of any subsequent structure of this type that
lacks the essential combination of bridge deck waterproofing, proper
drainage, adequate concrete cover to reinforcement/pre-stressing
tendons and grouting of tendon ducts.

So Hammersmith is very much a one-off. That doesn't mean that other
structures don't have problems of their own, but the design and
subsequent operation and maintenance practice related to the
Hammersmith flyover seems to have combined in a way that could only
end in tears.

I bet the DfT (or the Highways Agency) are glad that they they ceded all
the trunk roads within London to the GLA. I'm thinking it must have been
transferred at about the same time that all those random motorways within
London were downgraded?

Yes, when the GLA (and hence TfL) was established in 2000. It formed part of
what was initially called the GLRN (Greater London Road Network),
subsequently renamed the TLRN (Transport for London Road Network).

I doubt it, but it could conceivably have been a responsibility of H&F
council pre-2000, rather than that of the HA. I think it fell under the
auspices of the GLC in years past. Be interesting to know when the
quasi-literal rot started!


The original client for the flyover was London County Council. Design
was by G Maunsell and Partners and the flyover was constructed by
Marples, Ridgeway and Partners Ltd..

http://www.engineering-timelines.com...em.asp?id=1164