Cob: Earthquake.

[vtrac]

>  How do cob buildings do in Earthquakes. I have seen pictures of old
>buildings that have withstood many Earthquakes, but I have also seen brick
>buildings that have withstood earthquakes. Is it possibly the way a structure
>is built: curved walls, etc., or is it the materials that should be used
>within an earthquake area.  I am interested if anyone has any insight on this
>subject, whether it is technical, experience or observation. My name is
>Layth. I am going to be writing my master's thesis on cob. But I need a lot
>more info to figure where I should start. I appreciate your help.
>
>Layth.

Hi Layth,

I have heard a couple of differing opinions. One, that the monolithic mass
will not break apart as easily as would a building with lots of parts. On
the other hand some would say that a cob structure doesn't have enough
flexibility to withstand the movement of a heavy earthquake. There really
is no complete panacea to prevent earthquake damage in this case, but I
tend to side with cob as stronger in an earthquake. A curved wall is many
times stronger than a straight wall of the same material. In my cob
structure I have even added interior buttrusse on a longer wall that serves
as interior walls/room divider/shelf. A good friend of mine, Rasaq, from
Afganistan who has built "clay" homes there for a living told me that in
the earthquake zones in his country they build round homes for this reason.
I would think they have the experience. Secondly, walls are tappered so
that wall load is better carried by a wider base and the center of gravity
is more spread out. (I'm not a physicist).  Thirdly, a common cob building
technique is that the foundation sits on a rubble trench footing which
could act like ballbearings in the case of horizontal movement. I have
heard that the Pyramids were built on rubble trench footings and architects
recently have introduced rubble trenches for earthquakes. Finally, the high
amount of straw in cob will give it a high degree of tensile strength. I
know from experience taking down walls that this straw adds considerable
strength. We have also heard of many earth buildings in countries such as
Turkey  that collapse in earthquakes killing thousands. I suspect that
these are built with little funds and therefore the walls a very thin.
Probably they are also straight. It is also on record that in countries hit
by deadly earthquakes the better built earth structures such as churches
remain standing while everything else collapses. My gut feeling is that a
curvillinear structure would not completely collapse, but rather crack. I
would be more worried about the roof collapsing. Just a few thoughts.

Ian
Down to Earth Building Bee