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

[Ian Marcuse]

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
>
>
>_______________________________________________
>Coblist mailing list
>Coblist at deatech.com
>http://www.deatech.com/mailman/listinfo/coblist