[GSBN] Jumbo Bale Question

[John Glassford]

G ' day Martin

You said:

> I wouldn't let the 6:1 h/w ratio in the draft code decide the height limit.
> There are ways to extend that ratio.  The Pakistan houses employ very stable
> 8:1 ratio walls just by using opposing external bamboo "pins".  Jumbo bales
> (laid flat) at 8:1 would yield a 32' high wall (almost 4 story).  You just
> need 32' tall bamboo!  Or more likely steel external pins?

Yes external all thread is what we use in pairs every 1.8 metres and
at window and door openings a pair each side.  We can go as high as
you need with the rods using joiners.

See:  http://glassford.com.au/main/?page_id=1364  {8'x3'x2' Bales on
their flat and in one pic you will see the rods}

>
> More realistic though, is the practice of dividing tall walls into stacked
> shorter walls with box beams.

We get to 6 metres without any additional top or middle plates using
jumbo bales in this case 8'x3'x2'8" on their flat strings up.  To get
to 32' we would need to use a middle plate system.  That would give
stability for the next level.

>
> As another point of comparison, the maximum aspect ratio for adobe
> construction in the International Building Code (2109.8.4.2) is 10:1. Straw
> bale codes to date have used a limit of 5.6 to 1.

Which code mate?  This does not apply to us here although we use the
original work from Pima County?  as a guide only for our engineers.

You see the density of these jumbo bales is far superior to the
standard 900mm x 450mm x 350mm bales we use.  I do not know just how
much these jumbo bales can support so far we have only gone to 6
metres high however I strongly believe that they will go much higher
if needed.  The trick will be to stabilise them while erecting them.
I have used the bales themselves to form a scaffold, jumbo bales that
is, and they also acted as a stabiliser for the construction.  Very
safe scaffold!!!  See:

http://glassford.com.au/main/?page_id=272

>
>>> The same goes for structural data on what a 4'(w) x 3'(h) x 8'(l) bale can
> hold up.
>

We have used 8'x4'x4' bales to 4.8 m high supporting a timber truss
roof with iron cladding with a span of 18 metres no problems.

> At least in theory, it is the skins only that determine an SB wall's bearing
> capacity, because the plaster skins, not the bales, carry the load (as the
> stiffest element of the wall assembly).

Not so in practice mate.  What happens is that the render creeps
downwards around 7mm over 2.7m high.  We conducted creep tests at the
UNSW and we only did the test using cement renders however lime and
earth would do the same.  So in effect the render has moved away from
the load bearing top plate and the bales are really doing the work.  I
doubt that you could get two string bales to perform like the jumbos
in fact I know you cannot.  What I mean is that a jumbo bale wall at
900 mm wide with a 1 metre top plate will support a much bigger load
than a standard bale however maybe these jumbo bales need a test or
two?
>
> I do think in the case of jumbo bales, it's also worth considering their
> unplastered bearing capacity.  This is a great quality of all SB walls,
> regardless of bale size.  That they have reserve bearing capacity that would
> very likely avoid wall failure if the plaster (or other load bearing system)
> is compromised or fails.  But jumbo bales have such a wide footprint, it's
> especially worth looking at them unplastered.

Agreed.

> Assuming normal bale density, I would say walls of unplastered jumbo bales
> laid flat can support 400 lb/ft.  They could support this either
> pre-compressed or not.  The only question is how much the walls will
> vertically compress under load.  I arrive at this number by using an
> allowable load of 100 lb/sq.ft., taken from the low end of a 70-287
> lb/sq.ft. range in various unplastered bale load tests (that range includes
> a safety factor of 4 relative to ultimate load).

Yes but in practice the density of jumbo bales is greater than
standard two string bales not sure of three stringers as we do not
have them here.  I would also suggest that they also weigh more per
cubic metre than two stringers.

We are also using 8'x3'x2' bales load bearing on edge to give a wall
2.9m high and 700mm finished.  This is a hybrid method we are using
see:

http://glassford.com.au/main/?page_id=1267

I see a great future for jumbo bales of all sizes especially the
8'x3'x2'8" variety.  This size is becoming more of the standard around
here for the local cockies as they can get three bales wide on a semi
trailer which is within the law; size wise.  John Deere have brought
out a new baler for this size of bale.  New Holland also have one as
does International Harvester I believe.  Most common of the jumbos has
been 8'x4'x4'.

Apologies for the cross from imperial to metric I am sure that you are
all ambidextrous!.

Kind regards
John Glassford
Huff 'n' Puff Constructions
http://www.glassford.com.au
61 2 6927 6027
In Australia (02) 6927 6027

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