[Cob] re Next Step (Janet Standeford)

[howard at earthandstraw.com]

It will be hard to beat a cob house on a rubble trench.  Every joint between bags is a weak point in an earthquake.  Rammed earth too will shift on the lift lines, not cob. 


Howard Switzer, Architect
668 Hurricane Creek Road
Linden, TN 37096
931-589-6513
www.earthandstraw.com
  ----- Original Message ----- 
  From: Kathy Dunster 
  To: coblist at deatech.com 
  Sent: Wednesday, January 13, 2010 4:03 PM
  Subject: [Cob] re Next Step (Janet Standeford)


  He was looking at low-cost housing alternatives for survivors of the 2006
  tsunami in Sri Lanka, obviously seismic stability is important in that
  region.

  Direct link to the full 182 page Daigle thesis is

  http://www.earthbagbuilding.com/pdf/Daigle_Bryce_C_200809_MScEng.pdf


  "It was determined that the compressive strength of *unplastered* earthbag
  housing specimens meets or exceeds the vertical compressive strength of
  conventional stud-frame housing technology using a variety of fill
  materials, with the greatest strength being observed for soilfilled bags."

  Note "unplastered" as he concludes more work needs to be done on plastered
  earth bag buildings as in a good shake the plaster would probably fall off,
  but would not compromise the integrity of the building's structure.

  He also concluded that

  1. "Stack height affects the strength and stiffness of earthbag specimens,
  with taller stacks (i.e. 6 or 9 bags) exhibiting lower strength and
  stiffness values, as well as different load-deformation behaviour than
  shorter stacks (i.e. 3 bags)."

  2. The testing procedures outlined in ASTM E 447 are inadequate for testing
  earthbag specimens due to their reliance on 3-unit stacks which may
  overestimate compressive strength.

  3. Soil-filled bags measuring 457 x 762 mm require loads in excess of 840
  kN to reach bag failure (defined as a loss of fill leading to reduced
  compressive load-bearing capacity). This is also true for soil-filled bags
  measuring 508 mm x 914 mm.


  -------------------------------------------------------
  Kathy Dunster
  Denman Island, B.C. Canada
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