[GSBN] Compression

Rikki Nitzkin rikkinitzkin at gmail.com
Fri Jun 5 13:50:53 CDT 2015

Hi André, 

this is good news that the French Network will be testing Load-bearing walls. Most of the tests done until now have been in the US (I believe) and done on larger bales than the European ones.

I have no suggestions on the technical part about how much pressure needs to be applied and how to measure it, however (just in case) I would remind you that if you wish to do so- and for all load-bearing test- it would be important to know the density of the bales before compressing them.

sincerely, Rikki

> El 3/6/2015, a las 0:00, Derek Stearns Roff <derek at unm.edu <mailto:derek at unm.edu>> escribió:
> Best wishes, André, in meeting the still-undecided requirements that you will face for this testing.  I think you will be able to apply the needed amount of compression force with various kinds of straps.  If you need more force, you can add more straps, decreasing the spacing between them.  However, I am skeptical that you can get a reliable reading of the total compression force on the tested SB wall section via a strap tensioning device like the one that you linked.  
> As we know, a bale stack is subject to compaction (decreasing space between the bales), and each bale can be compressed (decreasing the spaces within each bale).  I’m sure that most of us have seen very tight straps (that are compressing a strawbale wall) become much looser over the course of a few hours.  Initially, each new strap that is tightened decreases the tension on the previously-tightened straps.  I don’t think you can derive an accurate measurement of the compression force on the whole (tested) wall section via tension applied to each strap, unless you can determine the tension on each strap simultaneously (or in quick succession), after all straps have been tensioned.  There are methods for testing the tension on a strap by measuring the force needed to cause a given deflection in the strap over a small length of the strap (for example, 100mm).  You might be able to adapt something of this sort.  
> Threaded rods have been used by the Steens and others to apply compression.  Since you may need to transport, set up, and take down the compression testing system multiple times, it might be simpler to do something similar with lengths of chain and eye-bolts, rather than long threaded rods.  Making multiple tension adjustments to your compression testing setup is probably easier with a threaded rod/bolt and nut system, than with straps.  
> A possible shortcoming of a testing protocol which applies compression to a strawbale wall via straps or similar tensioning devices, is that amount of compression constantly changes over short time periods, as the walls compact and the bales compress.  This contrasts with loading weight onto a wall, as would happen in a house with the addition of the roof and possible snow loads.  The pressure on the wall due to a geven amount of weight will not change with compression and compaction, so in this regard, compressing with straps doesn’t fully simulate the normal loading of the walls in a house.  If someone wants to challenge your testing, this could be an argument against a test method using straps.  Hopefully, your planned testing with twice the load expected in the final house will take care of concerns about the compression loads changing somewhat during your field tests.  
> Releasing the tension from the straps on a compressed wall can be dangerous.  Similarly, placing a large amount of weight on a wall (or pressure from jacks or a tractor bucket) creates a risky situation.  Your chosen compression method should include a safe way to address the large amount of potential energy stored in the compressed wall.  
> Keep us posted,
> Derek
> Derek Roff
> derek at unm.edu <mailto:derek at unm.edu>
>> On Jun 2, 2015, at 7:36 AM, André de Bouter <contact at lamaisonenpaille.com <mailto:contact at lamaisonenpaille.com>> wrote:
>> Hello Balers and Balesters,
>> The French SB Network is invited to participate in a testing program on loadbearing SB. We'd like to show that compressed unplastered SB walls can carry a decent load. Of course we know that this has been proven before, but hey, this is France, we have to prove that the same laws of physics and logic apply here as well, so that the French can accept it is true (you never know, eh? ;-).
>> The basic idea is that if we can show that such a wall is précompressed at, say, twice(?) the load it will carry in the future, it should be a safe bet that it will hold the future loads. I cannot yet explaine the details of what and how we want to test as they are not yet defined. We'd like to test unplasterd small, middle sized and big bale walls in order to mesure the ratio of reduced height relative to dry density of the bales and the applied compression.
>> a few plastered walls might be tested too.
>> I'm looking for is a cheap, secure and rapid way to compress the SB walls 'a whole lot', that can, preferably, be reproduced on building sites. And if possible in a way that one can predifine the compression load. 
>> I found this pneumatic strapping device :
>> http://www.central-strapping.de/francais/arrimage/pneumatique/pneumocord.html <http://www.central-strapping.de/francais/arrimage/pneumatique/pneumocord.html>
>> but it 'only' goes to 7500N (750kg - 1650 lbs)
>> I found straps that go 1170 kg - 2574 lbs
>> Comming acros this device I figured that compressing loadbearing walls would finaly become a controled piece of dense cake. But I wonder if this machine (for a 'mere' 2000€) has what it takes to compress enough.
>> We could also use mesuring devices under the straps, (maybe cheaper) but probably finiky.
>> Have any of you have found the 'perfect', controlled, compression method yet?
>> Any suggestions on how much you would press the walls and how big a safety margin engineers, building officials and builders insurance (our biggest hurdle in France) would consider ok?
>> Our starting point is to convince that a SB wall can carry 500kg (1100 lbs) per meter of wall (about 3 feet). Does a compression of 700kg - 1550 lbs 'impress'? or should the margin be much higher?
>> Cheers,
>> André - squeezit - de Bouter
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