Fwd: RE: [Cob] How wide should a cob wall be in earthquake zones?

[Ian Marcuse]

I was involved in the siesmic testing here in Vancouver. Though we 
are still waiting for the engineers report, one obvious finding was 
the extent of shear failure, but as you say, only at about 2 g-force 
(over 9 richter at the epicenter). Considering the massive force our 
model received, it held up very well. As a consequence of this test, 
City engineers here in Vancouver (a high siesmic zone) have asked for 
vertical reinforcement of some sort,  sticks, even just rope. I would 
say that bamboo would work well. A recent garden shed on City 
property, though under 100 sq. ft and not requiring a permit, was 
required to have this vertical reinforcement.

Ian Marcuse




>
>
>
>I can see having 2 ft or more thickness of wall but I dont know about the
>rebar reinforcment in the walls. From all I've read about cob is that it is
>very different in structure from Adobe or Super adobe. The nice thing about
>cob is it has no mortar between any brick. Its just one big homogeous wall
>held together by clay sand and straw. I believe in California they did a
>shake table test on a scale model of a cob house and it held up almost to a
>9 pointer before structuraly falling apart. I believe one book I was reading
>said the straw acts as the binder in these wall and create a lot of lateral
>shake stabilaty in the walls. I beleive Ianato and a few others have done
>some research on it but still waiting to get their book through the library.
>
>I will not be making my wall any taller than 8 ft. The buildings will be
>single story and no larger than 200 square ft. I plan on making about three
>structures one a living/kitchen/dining area one a bath house and one a
>bedroom conected by breezways. building will be no more than 6 ft apart. I'm
>going for curving walls and a very organic look.
>
>I'm thinking of buying a cement mixer then puting up a small shed to protect
>it and other tools from the elements before I begin the project. Any
>sugestions on which type to purchase? I would like to do most of the cob
>mixing in the cement mixer along with mixing clay plasters later in the
>project. Eventually I woiuld like to surround the whole structure in a cob
>wall to make a nice cozy courtyard with the rear sides of the building being
>connected to the courtyard wall. Think of an african Kraal and you may be
>able to picture about what I want to do.
>
>Question though, can a concrete footing be poured in phases or does it need
>to be poured all at once? I would like to do this myself but could hire a
>cement truck if necesary to come to the property.
>
>I'm prety much on my own building the structure. Any sugestions on how to
>get help in building it?
>
>I am also thinking of erectin the roof structure first and building the
>walls up to it. I'm looking at this as a long term project and hope that
>having the permanent roof on the buildings will alow me to work through the
>winter. Does not get to cold here so not to woried about it.
>
>Thanks again!
>
>David T
>-----Original Message-----
>From: coblist-bounces at deatech.com [mailto:coblist-bounces at deatech.com]On
>Behalf Of john fordice
>Sent: Friday, June 16, 2006 12:43 PM
>To: Whidbey Island Soap Co.; coblist at deatech.com
>Subject: Re: [Cob] How wide should a cob wall be in earthquake zones?
>
>
>David & All,
>Here are some SEISMIC STABILIZATION STANDARDS.  I've developed these based
>on some shaketable tested methods for adobe construction & they are very
>easy to include in Cob.
>
>Feel free to extend the dialog if you wish.
>
>john fordice - cob architect / builder
>
>...............
>WALL HEIGHT / WIDTH / LENGTH & OPENINGS   - when designing walls & placing
>window and door openings in the cob follow these criteria:
>cob wall height to thickness ratio of 7 : 1
>  taper 7:1 thickness to 12" wide at top - reduces upper weight of the wall
>buttress or thicken all open ends of cob walls to at least 2x the wall
>thickness
>maximum opening : wall length ratio of 1 : 3
>3' feet minimum from a corner to openings
>2' minimum wall between openings
>4' maximum opening width
>  wall shorter than 3' in length should not carry any structural  loads from
>above
>no concentrated beam loads into cob walls - distribute all loads
>
>EARTHQUAKE DESIGN - cob can be built to survive earthquakes - some basic
>earthquake design principals are:
>a continuous reinforced concrete perimeter footing - 12" deep x 18" wide
>minimum - minimum of 2 #4 horizontal rebar - - wider  with 3 #4 for walls
>over 8' tall
>a  mortared stone or Urbanite base wall - 16" minimum height above finished
>exterior ground - match cob wall thickness
>3/8" SMOOTH rebar vertical ties at 24" spacing in full height wall sections
>- embed in footing & hooked to a #4 cross bar in footing - full height of
>wall - attach to bond beam atop wall - thread top 6"
>cob wall height to thickness ratio of 7 : 1 - taper walls to 12" wide at top
>to reduce upper weight of the wall
>double 2x4  bond beam embedded in top of wall - vertical tie rod at  lapped
>corners  - stud 3 sides in wall w/ 16d nails at 3"-4" spacing.
>rafters at 24" spacing max - nail well to bond beam ( angle clips preferable
>) - solid block rafters at bond beam
>plywood or 1" roof sheathing - well nailed to create solid roof diaphragm
>assure continuity of connection between ALL structural components -
>VERY IMPORTANT !!!
>
>
>on 6/16/06 10:46 AM, Whidbey Island Soap Co. at Soap at whidbey.com wrote:
>
>>  Hi everyone!
>>
>>  I am going to be building a small home here in Washington State and would
>>  like to know how wide I should build the walls of a cob house in an
>>  earthquake zone. Also is there anytype of reinforcing I should be looking
>>  into? Someone here mentioned building the walls two and a half feet thick
>at
>>  the base and tapering them to the top for load bearing walls. How about if
>I
>>  support the roof with post and beam construction?
>>
>>  Thanks again!
>>
>>  David T.
>>
>>
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