[Strawbale] 3-string bales...testing, testing, testing...

[Matt Chase]

Hi all

I would speculate that very rarely would you find a situation where 
individual straws are breaking (snapping), especially when exposed to 
tensile forces, as per some of the testing apparatus suggestions that 
have been made.  I'm not sure what the relevance or usefulness of 
testing individual or bundles of straws in this manner would be.  
Generally, other forms of failure are observed, such as whole wall 
buckling, excessive deflections, or, in the case of plastered wall 
tests, delamination or cracking of the plaster.  In these cases, it 
would be the overall quality of the bale (density, baling etc.) and 
of construction that would govern the structural performance, not so 
much the ultimate strength of individual fibres.  It would be more 
appropriate to test on a larger (more realistic) scale.  Consider 
this: if testing were done to show that rice straw, for instance, is 
stiffer and stronger than other types, when tested fibre by fibre, 
would one still choose to build with shoddily manufactured rice bale 
or a dense, well-baled, wheat bale?  Additionally, I believe the 
testing has shown by now that strength of straw bale walls is not 
really an issue for one or two storey house-sized buildings: it is 
the quality of bales and quality of construction (which will lead to 
unacceptable deflection, plaster cracking etc.) that are the most 
important structural related issues.

Perhaps a more important goal related to the different species of 
straw would be to determine which species are most resistant to 
prolonged moisture exposure...

Matthew Chase

Message: 3
Date: Sun, 25 Mar 2007 22:41:39 -0700
 From: Chris Green <pojeros at telus.net>
Subject: Re: [Strawbale] 3-string bales...testing, testing, testing...
To: Strawbale at listserv.repp.org
Message-ID: <46075D13.8080409 at telus.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Denise Ohio wrote:
> <snip> I've read quite a bit of the
> testing data and wish I was a zillionaire so all of these ideas 
could be 
> tested thoroughly across an array of conditions.
One series of tests I would like to see is a comparison of the 
strengths 
of different types of straw: hemp, rice, wheat, oats, barley, flax, 
and 
so-on, perhaps in comparison to various fodder species ("hay")
I don't know if that has been done yet.
With hemp in there, the testing would probably have to be done by 
engineering students at Waterloo University, Fleming College, or some 
such place in Canada or Europe so we don't have to, ahem, bale out 
some 
college kids in the hemp-free States....

What I envision is some kind of calibrated machine/ gizmo that could 
pull on individual straws or bundles of straw until they break. Do 
that 
a few hundred times and one can come up with an averaged figure on 
how 
strong the different fibres are.
Or, following the spirit of Rob Tom, a simpler, gizmological free way 
to 
do this would be to clamp the straw on one end and clamp weights on 
the 
other, adding more weight until the straws break...that might not be 
as 
accurate as using a precision micro-calibrated hydraulic modulus of 
elasticity stress analyser thingie, but it would cost less.
Leaving more money to put in some students' pockets.

Maybe the straw bale community (us) should think about raising some 
funds to conduct this testing. I'll pledge (and mail!)  $20 if 
someone 
wants to organize it.

Cheers,

Chris Green.


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