Interesting Applications of Prestressing
Winterton House
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Information about this project, and all the
images shown here, were given to me by Whitby Bird and Partners for use
as teaching material in the Prestressed Concrete Module. Their assistance
is gratefully acknowledged. Copyright of the photographs remains with
Whitby Bird.
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Winterton House looks, superficially, like any
other tower block in London. But it is now an example of how prestressing
can be used constructively. It was originally built in 1968 with a concrete
service core, light steel external columns, and precast lightweight concrete
floors. It also had light GRP clading panels externally. Only four towers
were built using this system and the other three have now been demolished.
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In its original form, the building suffered from a number of problems.
The external cladding was unreliable; the thin floors and lightweight
partitions between the rooms and between the flats also gave rise to complaints
about lack of privacy.
The obvious solution was to provide better external cladding, with
heavier internal partitions. This would require heavier floors, themselves
a benefit, but this would have overloaded the internal core and the lightweight
columns.
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The solution, devised by Whitby and Bird, was
to strip out the building and build a new loadbearing brickwork skin.
This could be used to react an upwards pretensioning force applied to the
internal columns. This would also ensure that the old concrete core, the
steel columns and the new brickwork acted as a single composite unit to
resist lateral bending loads and to prevent differential temperature movement.
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The building, stripped back to its original
structural components. It was never originally seen like this since the
floors and cladding had been added as soon as the columns had been fixed
in position.
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The new vertical section. Compare this with
the original section above. Extra piles have been added to provide foundations
for the brickwork skin; the external brickwork has been added, and at the
top the transfer frame has been added. By jacking down on the brickwork,
this frame applies tensile forces to the internal columns, thus relieving
the core of the additional weight of the floors and internal partitions.
A recent paper in the Structural Engineer has suggested that the initially
applied prestress has dissipated due to creep of the brickwork.
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Seen from a distance, the frame seems remarkably
light, and its function is not obvious.
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The frame under construction and ready for jacking.
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Two views of the completed rebuilding.
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Further technical details of the project can be found in:-
Bird B., Watney Market Estate - Winterton House and Gelston Point,
Masonry International,
10/2, 41-45, 1996.
Bird A.B. and Hitchens M.J., Off-the-frame brickwork: Winterton House,
London,
The Structural Engineer,
78/10, 26-33, 2000.
Bingel P.R., Bown A. and Brooks J.J., Off-the-frame brickwork: analysis
of the data from Winterton House, London,
The Structural Engineer,
81/9, 27-33, 2003.
