Peter Johnson wrote:
On Fri, 13 Jan 2012 13:09:44 +0000, Roland Perry
wrote:
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.

I recall the Sunday Times getting excited about the M6 viaducts being
at risk of collapse in Birmingham, must have been in the 1970s or
'80s.


80s. The problem was that the client deleted the sliding bearings
that were needed to allow for movement, including thermal expansion
and contraction, and replaced them with grease. Literally.

Within months, the grease dried out and the beams seized on to their
supports. So movement was no longer possible and temperature changes
put massive stresses into the structure.


The M6 bridge over the M1 was propped about 10 years ago. I don't know
what weakened it: poor design, over-use or salt, could have been any
of them.


As with many highway structures, the vast increase in the allowable
gross weight of the biggest lorries has created no end of problems.
The damage done to the road itself is proportional to the fourth power
of the axle weight of the vehicle. There must be a comparable
relationship between gross vehicle weight and the effect on
structures.