[Cob] Curved bond beams

[john fordice]

Mitch,
As cob builders, our understanding of cob's ability to withstand  
seismic forces is  conjecture based on supposition.
In other words, we don't really know.  In the absence of tested proof  
that cob can withstand earthquake forces, i choose to include  
additional seismic stability components in the cob buildings I design  
& construct.  Based on some shake table testing of methods for adding  
seismic stability to adobe structures,  I wrote the following about  
seismic strengthening of cob:
.........................
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

  VERY IMPORTANT !!!  -  assure continuity of connection between ALL  
structural components.
..............................
happy mexico cobbing
john fordice  -  cob research institute



On Sep 25, 2008, at 12:44 PM, Mitch Ventura wrote:

> Just bought 5 hectares of land in Mexico and hope to build my cob  
> home near the end of 2010, which gives me plenty of lead time for  
> the planning. (Due to prior experience, I am a firm believer in  
> "measure twice, cut once".)
>
> My preference is to use solid wooden beams for the bond beam (live  
> in a seismic area), but I also want to make a house that is curved;  
> obviously straight wooden beams do not line-up well on bends.
>
> How would one best make a bond beam on the top of a curved wall  
> without having to resort to reinforced cement (or is that the only  
> viable and proven option)?
>
> Saludos from Iraq.
>
> Mitch Ventura
>
>
>
>        
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