Triaxial polytunnels

 Greetings, fellow urglers ;-)

I've made a page about triaxial polytunnels.

In particular I've created the following pages:

Triaxial index : http://hexdome.com/triaxial/
       Weaving : http://hexdome.com/triaxial/weaving/
    Polytunnel : http://hexdome.com/triaxial/polytunnel/
        Sphere : http://hexdome.com/triaxial/sphere/

It's probably best to start on the first link.

The material about polytunnels is what's likely to
be of interest to the denizens that inhabit this group.

Basically, I built a model of a triaxial weave
polytunnel, photographed it, wrote some material
about its significance - and then uploaded the results.

To quote from the introductory paragraph:

``Farmers do not need the wide spans and high spaces domes
  offer - for them, polytunnels make much more sense.

  I looked at conventional polytunnel designs. As far as I can
  see they make little structural sense. Their structural
  elements often rise straight into the air with little sign
  of support. As a result the designs often have to rely on
  the use of excessively rigid (and expensive) materials -
  and braces.

  Polytunnels represent an /excellent/ case for using triaxial
  weaving. Triaxial weave is light, resiliant, strong in all
  directions, /very/ resistant to shearing forces - and yet
  still easy to construct.''

As I go on to argue:

``For a given strength, an intelligent structural design
  allows substantially lighter (and cheaper) materials to be
  used. In particular, polytunnels of reasonable size can be
  constructed along these lines using PVC conduit - which is
  an astonishingly inexpensive material. [...]

  Polytunnels facilitate growing sensitive, tropical
  fruiting plants in northern climes - where much of the
  planet's landmass and population reside.''

Thus, I consider polytunnels to have significant economic
importance.

It's my hope that I can contribute to making many of them
cheaper.

Enjoy,
--
__________
 |im |yler  http://timtyler.org/   tim@tt1lock.org  Remove lock to reply.

 Tim Tyler wrote:

OK: that makes structural sense, given cheap enough materials. But
have you put _time_ into your calculations?

Mike.

 
My model took me an hour and forty minutes to construct - and
twenty minutes to dismantle.

Basically, triaxial weaving is simple - to the point of being
trivial.

The construction process is a bit different to the building of
a conventional tunnel, though.

The structure is typically constructed flat on the ground -
and then gradually pushed/lifted into shape.

If the structure is of any size, the lifting would be a
progressive process - using a mixture of ropes from the outside,
stakes to pin in the far edge - and perhaps props from the inside.

I think it even makes sense put the polythene in place (and
hold it there using pegs along the edges) while the structure
is lying flat - only battoning it down after erection.

This avoids any need to clamber up onto the top of the
structure while positioning the polythene - i.e. these
steps:

http://www.murcrusto.eclipse.co.uk/polytunnel2/page_02.html

...and makes adding an insulation layer in the process a
more practical proposition.
--
__________
 |im |yler  http://timtyler.org/   tim@tt1lock.org  Remove lock to reply.

 
/snip/


I haven't got round to looking at your pages yet - but I will. I mention
this just in case you've suggested this...

Have you thought of pegging (preferably burying the bottom of) one edge
of the polythene and folding it away from where you are having the
tunnel?

Construct your lattice on the ground where the tunnel is to go, then
erect it, and afterwards, pull the membrane over it?

It wouldn't work in my garden, as it's far too narrow to lay it flat,
sensibly, and is somewhat - er - mature.

http://www.users.zetnet.co.uk/hi-fi/garden.htm

It has been tidied up a bit, but things will keep growing, despite the
best efforts of the resident molluscs.

--
Rusty
Open the creaking gate to make a horrid.squeak, then lower the foobar.
http://www.users.zetnet.co.uk/hi-fi/

 
It looks sensible for a permanent structure, but for a small garden
polytunnel of the type that you use as a cloche, rather than walking into,
you need some way of making it collapsable. The typical concertina type can
be folded into a small package for storage but I think it would be more
difficult with your design which looks ike it would be strong against
compression in all directions, not just in the directions needed. a normal
polytunnel with a guy rope at either end keeping it in tension would be more
practical I think.

Have you looked at the pop-up childrens play tents? They seem to be very
cheap to make and a reasonably sized tent which will easily hold a child can
be folded with a neat twist into a package not much larger than a dinner
plate. maybe the same sort of approach could be used to make your tunnel
collapsable.

--
Martin & Anna Sykes
martins.garden@sykesm.xglobalnetx.co.uk ( Remove x's  when replying )
<http://www.users.globalnet.co.uk/~sykesm>