[Strawbale]Some loadbearing compression ideas/questions

[Tim Owen-Kennedy]

Hi All,

With regard to pre-compression, creep, pre plastering post plastering and
cyclic vertical loading (snow loads) you might want to look at that part of
the test we did as EBNet. Go to www.ecobuildnetwork.org and click on the
straw bale testing program link in the upper left hand corner. This will
take you to some of the reports from the tests that we conducted. The test
to which I am referring is title "load-bearing and Creep".

Best of luck as we all discover how best to build plastered straw bale
structures,

Tim


Tim Owen-kennedy
Vital Systems, Natural Building & Design, Inc.
888.859.6336 PO Box 751, Ukiah, CA 95482

-----Original Message-----
From: strawbale-admin at amper....muni.cz
[mailto:strawbale-admin at amper....muni.cz] On Behalf Of Stewart Hargrave
Sent: Thursday, May 05, 2005 4:02 AM
To: strawbale at amper....muni.cz
Subject: Re: [Strawbale]Some loadbearing compression ideas/questions

On 27 Apr 2005 at 11:15, rikki nitzkin wrote:

> HI all,
> 
> Some thoughts about compression for you tecnical people.  I have been 
> thinking about these techiniques that are popping up as ways to reduce 
> compression on loadbearing walls.  Specifically the techniques like those 
> used by Tom Rijven, or the man in ávila:  they use clay paster on the
walls 
> before or during the wall-raising.  This solidifies the walls and they
don´t 
> compress.  This has obvious advantages because it protects the wall at
once, 
> and you don´t have to leave gaps above or below the windows and doors, and

> if you build the wall well you don´t have to worry about uneven
compression, 
> etc.  SOunds good, huh?  But the other day I was thinking (I do that once
in 
> a while) and I thought to question:  A compressed wall is sure to be 
> stronger, no?  it may be more comfortable avoiding compression, but will
it 
> not make the walls weaker and capable of bearing less weight? On my 
> load-bearing walls I have a clay-tile roof, I don´t know if I could 
> recommend putting a heavy roof on an "uncompressed" loadbearing wall . . 
> .But in the testing people have done they say that the plaster bears more 
> weight than the bales themselves, some maybe my doubts are irrelevant . . 
> .What do you all think?

I was reflecting the other day about the construction of a Formula 1 car.
These 
are made out of thin carbon fibre - the strongest parts of the car are made
from 
two thin layers of carbon fibre separated by a weak core material a few mm
thick, 
making the whole very much stronger than the sum of the parts. The essential

element is the gap between the two thin layers - on their own the thin
layers will 
bear much less compressive and shearing forces, but as long as a stable gap 
can be maintained between them, their combined strength is very much
greater.

It seems to me that in some respects, this is not so different to a
load-bearing SB 
structure - two thin layers of stucco separated by a core of straw. Now
carbon 
fibre is much stronger under tension that stucco, but that may not be an
issue 
under load-bearing conditions.

The point is, much evidence suggests that the stucco takes most of the load,

rather than the straw, so once two layers of stucco are applied, the
tendency for 
the straw to settle down may not be as much of a factor as you may first
think, 
and the two layers of stucco acting in conjunction with the straw core
provides a 
strong enough support.

I should point out that this is not an expert opinion, just an idea I had.

-- 
Stewart H.

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