[Cob] Difference between cob and rammed earth (reinforcing)

[Peter Ellis]

   While the general public isn't particularly looking for curved wall
   houses, that's not necessarily a sign that they do not want them, but
   rather that they are not available.  Make houses available that are
   environmentally friendly, energy efficient, aesthetically pleasing and
   that don't look like a collection of boxes stuck together and one
   might find that the general public is actually quite interested - if
   the price is comparable to a "conventional" house.

   And a note about rammed earth - it doesn't have to use portland
   cement, lime works in rammed earth and some soils are apparently
   capable of forming stable rammed walls without the addition of either
   lime or cement.  It's also the case that there are rammed earth
   structures still standing that are hundreds of years old.

   I think rammed earth works better in larger structures than does cob,
   and that much of the division between the two methods of construction
   is really a matter of aesthetic.  Cob lends itself to a very personal
   involvement in, literally, sculpting the structure, while rammed earth
   is more structured, less free form, and in a sense more "mechanical".

   Peter
   >From: laythss at yahoo.com
   >To: coblist at deatech.com
   >Subject: Re: [Cob] Difference between cob and rammed earth
   (reinforcing)
   >Date: Sat, 11 Dec 2004 00:37:40 -0800
   >
   >Ian,
   >   WHat I am trying to do in my thesis, is to see the eligibility of
   >cob (among other earth buildings) to be used in the mainstream
   >residential housing.  My only problem (for the general public) is
   >the test that was made in BC was for a round structure.  A round
   >structure is known to be stronger than a rectangular structure.
   >This is all good for the exception that a round (curved wall)
   >structure is not so much a main-stream structure.  and yes using
   >rebar might not be the smartest thing, yet with my limited
   >engineering background I think it is still better than building with
   >wood or concrete, since they impact the environment far more than
   >cob or cements/earth rammed earth structures even if they are
   >rebarrred.
   >Ocean in regards to rammed earth, the cement/rammed earth uses
   >between 5%-15% cement in it, isn't this better than a 100% cement
   >structure environmentally. I know it is not the best, but wouldn't
   >be a good start?
   >
   >Layth
   >On Dec 10, 2004, at 10:01 PM, Ian Marcuse wrote:
   >
   >>The structure was about 5ft tall 6 ft diameter. The walls (8
   >>inches), roof, doors, everything was scaled down in proportion and
   >>the test was of course calibrated (or whatever the word is) for
   >>this size structure and to make the data relevant to a larger
   >>building. The roof was loaded also to represent an actual building.
   >>We did not build a foundation though which would have given us much
   >>different results I am sure and would be a very important test to
   >>conduct at some time. We are hoping the engineers are preparing a
   >>report though I have not heard anything yet. At a 7.2 quake, we had
   >>minor cracking, and yes the word from the experts is that we are
   >>due for a 8 plus quake in the Vancouver area, which could result in
   >>major damage to cob. A 9 plus, probably most building will come
   >>down, but the interesting thing about our test was, had someone
   >>been inside they would have survived. Some cob chunks fell away
   >>from the building because of the curved nature of the building.
   >>They did not fall in. Also enough of the walls remained to hold the
   >>roof up. The shake of a 9 plus quake is violent. It was amazing and
   >>I doubt many stick or brick building would have held up at all. Cob
   >>may not totally collapse, but it would likely be damaged beyond
   >>repair. The engineers, including city engineers were very impressed
   >>by cob's performance in a quake. I think we have gotten over that
   >>hurdle with city officials here in Vancouver. We hope to make the
   >>report available to others when complete.
   >>
   >>Ian Marcuse
   >>
   >>
   >>>I think reinforcing with bamboo is a great idea.  I keep reading
   >>>that a cob
   >>>house will withstand a 7.x earthquake at least as well as a
   >>>wood-frame
   >>>house.  But we in the Pacific Northwest are overdue for an 8.x, or
   >>>maybe
   >>>even a 9, earthquake.  If we get one in my lifetime, and all the
   >>>wood-frame
   >>>structures in my town collapse, I'd like for my cob house (so far
   >>>still a
   >>>sparkle in my eye) to be still standing.  After all...it might
   >>>have to serve
   >>>as the local hospital for awhile!
   >>>
   >>>I do have a lingering curiousness about your earthquake tests.  Of
   >>>necessity, you used a small structure...was it 5 feet tall?  Any
   >>>small
   >>>"thing" will be stronger than a larger "thing".  So a 5' structure
   >>>will
   >>>withstand a 7.2 earthquake much better than a 10' structure.  I
   >>>assume--and
   >>>please correct me if I'm wrong--you compensated by building the
   >>>walls
   >>>narrower than you would a real cob house.  Did you have to do
   >>>anything else
   >>>in order to make your results reflect how a real house would
   >>>behave?
   >>>
   >>>Thanks,
   >>>Bonnie in OR
   >>>
   >>>-----Original Message-----
   >>>From: coblist-bounces at deatech.com
   >>>[mailto:coblist-bounces at deatech.com]On
   >>>Behalf Of Ian Marcuse
   >>>
   >>>
   >>>Reinforcing cob in earthquake zones is probably a good idea.
   >>>Bamboo
   >>>would work fine I think, embedded vertically would help to prevent
   >>>shear failure. In our recent earthquake tests at UBC this year,
   >>>the
   >>>need for this type of reinforcment was quite clear. Mind you at a
   >>>7.2
   >>>richter quake the cob held up briliantly without reinforcement,
   >>>apart
   >>>from straw. At a >9 richter, the building seriously failed, but
   >>>without roof collapse. A 9 quake is however extremely rare. If you
   >>>have bamboo, I doubt that it would hurt. Does anybody have other
   >>>thoughts on this?
   >>>
   >>>We hope to post a video of the quake test on the web soon
   >>>
   >>>Ian Marcuse
   >>>
   >>>
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   >>
   >>
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