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RE: GSBN:Compression & bumble bees

Hi Maren
It has to be made clear that the tests done in Germany showing the need for
so much pre-compression (30%) are not borne out in practice. They are very
interesting results and we need to understand them, but we have built a 2
storey loadbearing house that remained unplastered over the winter - that
is, had it's full load on the walls for several months - and the maximum
compression we had on the ground floor walls was 6%. We  know from many
practical experiences that loadbearing walls do compress a certain amount
under their full loading, that most of this happens in the first 2 weeks,
and that it has virtually stopped by 6 weeks. On top of this, there is the
effect of plaster on the walls, which definitely has an effect to reduce the
amount of compression experienced if it is applied before the 6 week period
is over.

A useful observation from the German tests however is that loadbearing bale
walls do not require plaster in order to make them structurally strong,
which should add to the debate in the US on this subject.

I think it is always useful when conducting research in laboratory
conditions to check in with what happens in practice as well. Hence the
inability of the bumble bee to fly analogy.

Best wishes

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-----Original Message-----
From: GSBN [<a  target="_blank" href="mailto:GSBN@...]On";>mailto:GSBN@...]On</a> Behalf Of Rene Dalmeijer
Sent: 22 August 2006 09:15
Subject: Re: GSBN:Compression


I just visited the FASBA (German SB association) gathering in
Walthershausen where 2 presenters focussed on this subject based on
laboratory testing trying to determine how much pre-tension is required
to avoid creep with unplastered bales. Basically what it boils down to
is that you need 30% pre compression on 100kg/m^3 dry density bales. ie
practically impossible. At the same time though I must clearly state
that the tests being done are very useful and will give us some very
useful data on the behavior of unplastered 2 string and Jumbo bales.

John Zahng of Australia has done similar plastered full wall tests and
found that about 4% pre-compression is required to avoid initial creep.
This figure roughly corresponds to what has been found in practice to
be the right amount of pre-compression. Incidentally the
force-deflection curves presented at the Fasba gathering exhibited the
same flow as those found by John Zahng.

On Aug 22, 2006, at 06:54, Maren Termens wrote:

> Hi all,
>   does somebody know which pressure per area  it's needed to compress
> Nebraska-walls? Or can you tell me which pressure are you normally
> using? I'm looking after essays and tests which work with this item, I
> couldn't find technical information about that.
>   Thanks a lot.
>   Maren
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