[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

RE: GSBN:Compression & bumble bees



Ahhh, compression....the squishing of bales.  30%????!!!! 

Barbara's observations concur with everything I've heard, seen and measured
from the field--around 3-6% squishing under gravity loads (depending upon
the quality of bales), most of it happening in the first weeks.  With our
Kalifornia Terminator Bales (TM), we have to work really hard to get 2%,
using jacks and levers. This is commonly called compression, but I would
suggest that the bales are already quite compressed when we put them in the
walls.  It appears self-evident to me, that the majority of this "creep" has
to do with the bales settling in to one another, rather than squishing.
This is an important distinction.

Thirty percent compression, as the German Scientists suggest, is....well,
Barbara said it politely: "I think it is always useful when conducting
research in laboratory conditions to check in with what happens in practice
as well."

About plaster, Barbara went on, "A useful observation from the German tests
however is that load bearing 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."  That the bales would work without plaster isn't in dispute,
but nobody has suggested, except for a few of us after a long day and a
couple of beers, to forget about the plaster altogether. 

And since it's there, the plaster might as well work. Compression loads will
travel to the stiffest element.  In the case of our bodies, it's our bones
(endoskeleton) that are stiffer than muscles and skin, and so we don't
collapse, even when jumping off of bale walls.  In the case of a plastered
bale wall, the plaster skins are stiffer than the bales, and so they take
the load FIRST.  If the load exceeds the capacity of the skins, the skins
crack (bones break), and the load is then taken by the bales which, we are
reassured by German Scientists, they will do very nicely.  

In earthquake country, we figure that skins will take most seismic events
without too much damage, but in a catastrophic quake will become useless
before the quake is finished--at which point the bales will bounce around
but not break.  The plaster, being stiffer than bales, keeps your windows
from breaking every time the ground quivers.

Note: in order for this to work most effectively, the plaster skins would
rest on the foundation (rather than hang in air).  This is more true in
theory than practice, I think, because in reality the loads seem to transfer
in and out between the skin and bales.

The question of plaster skins isn't one only of gravity loads, however.
Walls also bend and stretch apart (in the wind and earthquakes), and bales
don't do very well when pulled upon. In that case the other element of
plaster skins, lathing, can be very important. By surrounding the bales with
a basket of mesh the walls are held together, and loads which develop in
tension are confined and brought back into the bale walls, in compression.
This is a Very Good Thing, and allows the bumble bee bales to fly like an
eagle.  It is also a subject of debate, because lathing costs (a little)
money and trouble, and because if it's METAL lathing, it might turn the
occupants into electro-jellyfish due to EMF, which would be a Very Bad
Thing.

John "Squish me in the Moonlight" Swearingen


John Swearingen
 SKILLFUL MEANS
design and construction
 www.skillful-means.com


-----Original Message-----
From: GSBN [<a  target="_blank" href="mailto:GSBN@...";>mailto:GSBN@...] On Behalf Of
Strawbalefutures
Sent: Tuesday, August 22, 2006 2:42 AM
To: GSBN
Subject: RE: GSBN:Compression &amp; 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
Barbara




WARNING: Strawbale building can seriously transform your life!

Amazon Nails
Strawbale Building, Training and Consultancy
Hollinroyd Farm
Todmorden
OL14 8RJ

Tel/fax: 00 44 (0)1706 814696
email: info@...
web: www.strawbalefutures.org.uk


-----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
To: GSBN
Subject: Re: GSBN:Compression

Maren,

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.

Rene
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
>
>
> ---------------------------------
>
> LLama Gratis a cualquier PC del Mundo.
> Llamadas a fijos y m?viles desde 1 c?ntimo por minuto. 
> <a  target="_blank" href="http://es.voice.yahoo.com";>http://es.voice.yahoo.com</a>
>
> --- StripMime Report -- processed MIME parts --- multipart/alternative
>   text/plain (text body -- kept)
>   text/html
> ---

>





-- 
No virus found in this incoming message.
Checked by AVG Free Edition.
Version: 7.1.405 / Virus Database: 268.11.4/424 - Release Date: 8/21/2006
 

-- 
No virus found in this outgoing message.
Checked by AVG Free Edition.
Version: 7.1.405 / Virus Database: 268.11.4/424 - Release Date: 8/21/2006