Cob: FW: Steel Frame?

[John Fordice]

Kristina and all,
I assume cob as infill to a steel frame building would work.
Until it was mentioned in this discussion,  I've not heard of anyone
building with cob in this manner.

I'll pose the question to you:
WHY ?
What possess you to want to do this ?

Is economy  the issue ?
Cob as a mass wall material is a lot of work & I wonder that adding
steel  to it will just increase the cost where it really isn't needed.

Is it to build under an existing shelter ?  This does make a bit of
sense, but tarps on poles are cheaper and unless you're building in
hurricane conditions should work just fine.

It seems to me that introducing a steel frame into a cob structure
pretty much negates the prime values of cob.

Some of the Prime Values of cob

Cob is simple.
It allows freedom of form..
Cob can be built using local  materials
It is VERY sustainable. 
It is low technology.
Making and building with cob consumes very little energy.

How well does steel meet these Prime Values ?
Steel in it's simplest and most economical form is the antithesis of cob.

Steel is recyclable (sustainable ? ), but only at a high environmental cost.
Steel promotes rectilinear form./  
To achieve freedom of form with steel is difficult.
Steel in NOT local and involves distant resources and transportation in
its manufacture and availability.
Steel is technology intensive.
Steel consumes lots of energy.

The value of steel is in it's strength, durability and ability to span
long distances.  With steel you need relatively less material than other
ways of building.   But if you really don't need the structural capacity
of steel, why build with it ?

Properly designed cob walls can be built as load bearing and no
additional structure is needed to support both the walls seismically and
the roof.
In fact, cob and other earthen materials actually perform better when
they are load bearing.
To build with cob as infill in a structural frame of some other material
is to actually create a less safe structure.

If you really need to build a steel building with cob as infill, have at it.
Just be aware that you are not using cob to it's full potential.
Be sure that you tie any long straight sections of cob wall into the
steel frame.  
In seismic areas straight cob walls without out-of-plane buttressing and
connection of the wall top to the roof diaphragm will be structurally compromised.

I wonder if anyone has studied the ductility of cob versus steel.  My
guess is that steel is much more flexible (ductile) than cob.  If this
is in fact the case, any steel frame acting as the structure both
in-plane and out-of-plane will need to be braced sufficiently to react
to seismic loads the same as the cob.  If not, there will most assuredly
be failure points at any cob to steel interface.

This is an area rich for discussion and research, but be careful.  

john fordice

Kristina Buss wrote:
> 
> On Sat, 9 Mar 2002, Kristina Buss wrote:
> 
>  Anybody know if it is possible to do cob over a steel frame with the roof
> already up? I know it is ok with post and beam but steel would be less
> expensive, use recycled material, and have less waste. Anybody tried it?
> 
> Kristina
>  kristinabuss at yahoo.com