Pull down cables
Using "push-down" valley cables can have some disadvantages
under some circumstances.
An alternative pattern employs "pull-down" cables.
These are cables that pull the fabric down from below -
rather than pushing it down from above.
To do that a cable sheath is required. This is stitched,
glued or welded to the bottom of the fabric.
Valley cables
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Pull down cables
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Pros and cons
Like the related flat pattern there are some
adavantages - and some disadvantages - to this pattern -
when compared to the use of push-down valley cables.
Advantages
- The cables are kept on the inside - which helps avoid
corrosion and thermal damage;
- The pull-down cables are better placed to interact with
internal structural elements;
- The cables can be thermally insulated from the main
membrane - helping to prevent heat damage.
Disadvantages
- Using pull-down cables incurrs additional
construction costs, due to the cable sleeves;
- Assembly is also more complex - due to the need to pass
the cables through the sleeves.
In many respects the key feature of the idea is that it
makes it easier for large anticlastic surfaces to be
pleated.
Anticlastic surfaces are important because they are light -
and can be constructed with tensile-only elements.
However, in pleated structures making anticlastic surfaces
requires that the membrane be pulled down from below - and
unless 'pull down' cables are used, that is difficult to do
without damaging or penetrating the fabric.
Examples
It's not always easy to tell from photographs whether
structures are using pull-down cables - however these
structures certainly look as though they are:
Myao Li Arena
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Myao Li Arena
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Talisman centre
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Talisman centre
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Both these structures feature large anticlastic surfaces.
It appears that pull-down cables have been used in these
structures because of the way they facilitate those cables
interacting with transverse interior cables.
Pull up cables
If you can replace ordinary valley cables with pull down
cables, it makes sense for you to also be able to replace
ridge cables with pull-up cables.
Although the elements in question appear to be compression
members, pleats in a membrane being pulled upwards appears
to be going on here:
Ichinoseki industrial centre
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Ichinoseki industrial centre
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