[Cob] structural engineer in Corvallis

[hms.mommy at juno.com]

On Mon, 06 Nov 2006 19:33:33 -0700 "Sarah Booth" <auntsariah at hotmail.com>
writes:
Any 
> of the more technical information along these lines that has been 
> generated 
> by other people working through similar situations would help us 
> greatly in 
> this struggle and be supremely appreciated!  

Sarah,
This is from John Fordice, who is working on code issues.  I believe this
is an adaptation of adobe codes for cob.  I'm sorry I don't have a better
reference for you; John is on this list, and is quite busy, but perhaps
he will have an opportunity to comment on the source of these criteria.

Cob Structural Criteria
 
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 to reduce 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’ 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 rebar in footing & hook to a #4 cross bar in footing. 
The rebar should go the full height of the wall and attach to bond beam
atop the wall; thread top 6”.
cob wall height to thickness ratio of  7 : 1 with walls tapered 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 !!!