[GSBN] Steel mesh in clay plaster + earthquake safe fire shelters

[RT]

On Sun, 25 Aug 2013 18:52:24 -0400, <GSBN-request at sustainablesources.com>  
wrote:
> Date: Sun, 25 Aug 2013 17:30:55 -0400
> From: oasis at oasisdesign.netre: Steel mesh in clay plaster + earthquake  
> safe fireshelters


> it only takes a few hundred pounds of wire to reinforce a 100,000 lb cob  
> building.

> What is properly sized reinforcement?

> Still being worked out, but 1/8" wire mesh on 6" centers is abetter fit  
> to  cob than say, 3/8" rebar on 18" centers.

> (wire mesh) has a high likelhood of a) enabling the thing to get a  
> permit and be built

Y'all;

It would seem that the third sentence (quoted above) negates the validity  
of the first sentence.

I know nothing about designing/building with cob simply because its  
thermal performance makes it unsuitable for use for energy-efficient  
buildings in my climate (~8700 HDD/yr) so I've not looked at it in depth.

However, I do know that in the design of reinforced concrete structures,  
6" x 6" x 6 gauge welded wire mesh would be utilised only as secondary  
reinforcement to control temperature and shrinkage cracking.

I also know that for reinforced concrete, the ratio of the cross sectional  
areas of reinforcment : concrete matters -- too much reinforcement can  
result in sudden destructive failure of the concrete -- too little  
reinforcement is essentially no reinforcement and can result in  
catastrophic failure of the structure.

"A few hundred pounds" of wire mesh to reinforce 50 tons of cob whose  
thickness is presumably a foot or more sounds like a case of the latter --  
essentially a case of trying to use T&S reinforcement as primary  
reinforcement.

Quite frankly, I suspect that straw or other fibre in the mix is probably  
more effective at the task of T&S than either 6x6 or chicken wire mesh and  
that a bamboo grid (whose spacing/placement/detailing has been properly  
designed) would be more appropriate for the primary reinforcement.

I also suspect that in most jurisdictions when seeking plans approval,  
approaching the Chief Building Officer with alternative reinforcement  
strategies that were developed by the U.S. Army Corps of Engineers would  
be looked upon more favourably than a scheme with no engineering  
documentation and mostly anecdotal support.

=== * ===
Rob Tom					AOD257
Kanata, Ontario, Canada

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