[Strawbale]Testing loadbearing straw bale structures ++ Need HELP for conception ++ Questions at the end

[Dirk Scharmer]

Dear collegues!
We're preparing a couple of tests of loadbearing strawbale structures.
Our main intention is to proove, that unplastered straw bale walls are
able to resist vertical and lateral loads coming up in two-storey
buildings (one-storey consumes to much space in small germany). Dietmar
Lorenz sent me the recent ebnetsbresearch documentation, but
unfortunately I was not able to get suitable information out of it/ to
apply the results to our german conditions yet. (If you want to have a
look on the texts I know, see
www.fasba.de/downloads/loadbearingandcreeping.pdf, I read the
cyclic-wall test documentation too, but I think it is not concerning for
our task)

Our current concept deviates a little from the previous test layouts:
See a sketch of our considered wall specimen:
www.fasba.de/downloads/specimen1.pdf.
As you can see on the sketch, we want to test an element of 2m width and
3m height with high precompressed bales. In the first step we'll work
with small jumbo bales (0,85mx0,5mx2m). That means in every course there
is only one bale (no running bond). This not only our test specimen but
also our wall element on the buildingsite.

Here are reasons for our election:
1. Based on the consideration, that our common 2-string bales should not
loaded above 15-19KN/m2 (and this is only possible by excellent work of
the baler, which is difficult to guarantee) and based on the calculation
that a typical german 2-storey- building with strawbales in the roof
shows a maximum load at the root point of more than 35-45KN/m2 we'll
first test the small jumbo bales with a much higher density.
2. According to the wet climate in germany, we want to have the option
to build very fast with prefab elements (but it should be also possible
to build the elements on the building site). These prefab elements
minimizes the time exposed to possible rain to 2 days. After fixing 6 to
8 elements in normal rectangular floor plan, you can immediately
continue with the ceiling,.... Building the exact labour intensive
openings comes after the completion of the roof. We think more bigger
prefabed wall elements need to much effort to give enough stability for
hanging on cranes clamp.
3. The reduction of the static requirement to an 2m-width element gives
hopefully more freedoom in designing openings in the walls, especially
for the southsided walls for passive solar winnings. In the output there
should be more openings possible, and you  don't need to consider about
the distances between doors, windows, enough undisturbed wall length.
4. We think prooving the stiffing Qualitys of earth or lime plaster
would nearly be impossible under german/ european building codes. We
prefer earth plaster, so in this case, it would be impossible to make a
safe definition of the mixture, the execution and the resulting
stiffness of it. So we decided to try our work with unplastered bale
walls, hopefully with sufficient results. If not this 2x3m wall element
gives us the chance to add wodden tie rods on each side to stiffen the
element.
5. The thickness of 0,85m is very high, so reducing the utilisation of
the thick jumbo bales on the 2m elements gives more space. Between the
thick 2m-elements we can you use 2-string bales (0,35m) on edge.

Besides that we'll test small 2-string bales, too but we're not
expecting good results, probably they'll work only by using plaster.
We'll work together with a small institut at the University of Applied
Sciences in Magdeburg.

So after 1,5 hour writing I would be very happy to get some feedbacks
from experts (not only). 
What do you think about our test layout/ our concept?
Will it be possible to proove precompressed unplastered bale walls for
loadbearing use (vertical  a n d  horizontal loads, no earthquake)?
Do you think our choosen way, not to build bale walls in running bond
with openings included is a possible solution?
How do you calculate the resistance of bale walls against lateral loads
(wind)?

Thank you very much for your attention

Dirk Scharmer

German strawbale association www.fasba.de


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