Cob: Earthquake.

[BOB LUITWEILER]

I wish we had some more definitive answers to earthquake "proofing" cob
buildings.  I certainly don't but would like to throw a few idea into the stew of
speculation.

1. Please, everyone on this list, learn to be a researcher when you travel to a
region that has "primitive" buildings and earthquakes.  For example when you go to
the Near East visit eastern Turkey.  Perhaps with a student as interpreter, talk
to many people who have been through an earthquake about their buildings and their
experiences.  Ask which buildings came down, which ones did not, what their
foundations were and their shape. Do they build tapered walls?  Were there any
curved walls?  What kind of roofs did the buildings have?

2. Make careful notes.  Take pictures.  Bring this information  back to our
coblist.

3. I have a few bits of information.  In Managua, Nicaragua their central city had
a serious earthquake.  The buildings were adobe, not cob.  One of the most
devastating effects was not the just the buildings falling on people but the dust
was so thick people suffocated. Now it is illegal to build with adobe there.

4. I attended a village wedding in Turkey.  Part of the ceremony was a folk dance
on the roof of one of the houses with at least twenty people.  The roof was flat
and massive.  First there are timbers, then smaller sticks then clay and cob on
top.  I doubt anyone would survive under that roof in an earthquake.

5. In Syria some roofs were dome shaped.  I think they were coated with gypsum. I
was not tuned into studying mud based buildings then or would have asked more
questions.

6,  At present I am trying to get information on how to make thick straw panels
held together with gypsum. If they were made without crushing the straw they would
be quite light, being less dense they people under them might survive.  Hollow
straw would be good roof insulation. The gypsum would be much cheaper and more
environmentally friendly than Portland cement.  It would also make the panels more
fire resistant and rot resistant.  How strong they would be is another question
and they would not  be water proof.  A good waterproof cover would be needed so
they did not soften from water soaking into them.   The trusses holding them up
could be cast out of flattened straw which has quite good tensile strength.  I'll
give anyone asking details on this who is ready to try making a couple.  I am,
unfortunately, in a situation where I can not do this kind of experiment.

There are a number of companies making straw panels and straw boards but they use
industrial processes.  They make high claims for their end products as good
replacement for many things where wood has been used in the past from wall
partitions to stair treads to counter tops and furniture elements.  We are just
beginning to develop the potentials of fibrous materials so much of which has been
burned in the past.  In sustainable environmental communities almost no organic
materials will ever be burned.  Much will go into mulch and much into building
materials more sophisticated than straw bales.

Bob Luitweiler.
 
 

vtrac wrote:

> >  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