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

[laythss at yahoo.com]

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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