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[Cob] earthquake test video

Mark Piepkorn duckchow at
Tue Apr 1 18:23:31 CDT 2008


>The following blog entry came from the blog: LIVE
>The entry is titled: Earthen Architecture in Earthquakes
>Down To Earth Building Bee in Vancouver, BC, 
>Canada had a shake test on a half-scale model of 
>a cob structure done at the UBC Earthquake 
>Engineering Research Facility. It happened a 
>while ago, but they just posted video.
>The model was of a circular structure with a 
>shed roof, described as "about 6 ft diameter and 
>5 ft high"... not representative of houses in 
>the developed world, but a start for more 
>research. There was a small window on the rear, 
>which is easy to miss in the video. 
>(Fenestrations normally weaken a structure, so 
>they're important to include.) There also 
>doesn't appear to be a stemwall ­ highly 
>recommended for cob buildings, and another likely point of seismic catastrophe.
>A larger or other-shaped structure would have 
>performed differently ­ which is not to say that 
>cob wouldn't outperform many other building 
>methods. But a person needs to know how the same 
>structure, built from other materials, performs 
>before any comparisons can be made. In the 
>video, Carlos Ventura, director of the research 
>facility, said that the impacts generated in the 
>first part of the test "usually will destroy a 
>structure that's not properly done." Which means 
>that a structure ­ of any sort, presumably ­ 
>that is "properly done" would also have 
>survived. He goes on to describe it as a "satisfactory performance."
>None of which is meant to denigrate the research 
>and findings. Just showing (beyond anecdote) 
>that cob can perform at least as well as proven 
>materials and methods under seismic conditions 
>is an excellent victory. When we in the 
>developed world hear about loss of life in 
>earthquakes due to collapsing houses in places 
>where earth building is common, we tend to think 
>that earth building plus earthquakes 
>automatically equals death. But there's more 
>than one way to build with earth, just like 
>there's more than one way to build with anything else.
>This excerpt from the proceedings of The 1855 
>Wairarapa Earthquake Symposium in New Zealand 
>isn't surprising: "Within the highest intensity 
>areas, many brick, cob, and stone buildings were 
>seriously damaged, some collapsing during the 
>earthquake and many requiring demolition after. 
>However, there were a few brick buildings that 
>suffered little damage. Some wooden structures 
>were also seriously damaged and several 
>collapsed. Most wooden buildings, however, 
>seemed to have remained standing although many 
>were damaged by falling chimneys."
>In the Vancouver test, the first point of 
>failure appeared to be typical: diagonal cracks 
>radiating from the corners of the door. I 
>suspect the window at the rear of the structure 
>had similar behavior. At the end of the final 
>test (culminating in a massive 9.0 Richter), the 
>building was breaking apart into large pieces, 
>mostly diagonally ­ as would be expected under 
>these forces on this kind of shape. But there 
>was also horizontal failure between lifts, 
>suggesting that cob building may not always be 
>quite as monolithic as generally suggested ­ 
>though clearly far more so than typical unreinforced, unstabilized adobe:
>Compare the preceding to this reinforced adobe shake test:
>Also see this video from the Getty Seismic Adobe Project:
>and the article When the Earth Moves: The Getty Seismic Adobe Project.
>Another video, from GVTV, in addition to 
>offering a couple technical misstatements for 
>the sharp-eared, shows some of the Vancouver testing.
>A couple interesting further reads are the 
>articles Making the Building Code Work for Cob 
>by architect John Fordice, and Some Thoughts on 
>"Adobe Codes" by seismic engineer Fred Webster.
>I'd be very interested to see strawbale get the 
>shakes. There have been a few crunch tests done, 
>but nothing like this yet, to my knowledge.