[Cob] earthquake test # 2

[Ian Marcuse]

Re: Siesmic Test # 2

As some of you may recall, we tested a scale model cob building on a 
siesmic shake table a few weeks ago at the University of British 
Columbia. The building received a massive pounding, but did not 
simulate an earthquake as it was supposed to, due to problems with 
the hydraulics. Despite the massive pounding, the building received 
only minor damage.

Today, with the hydraulics repaired, we successfully conducted our 
tests. The model, which was about 6 ft diameter and 5 ft high, easily 
handled a 7.4 richter quake with only minor cracks. And this was 
after the previous pounding that certainly compromised the structure 
for todays testing. This quake simulated a particular quake in 
California that was particularily destructive to buildings. Finally, 
the building was given a 2 g force shake, something closer to a 9 
richter and at the epicenter. As was expected the building was shaken 
apart. This would be a very rare quake and no building would easily 
survive this level of quake.

Amazingly, despite such a violent shake, the building remained 
standing, though large chunks of cob had fallen away from the 
building. Anyone inside would have survived as the roof remained in 
place and no large cob fell inward. There was considerable rocking of 
the building from side to side which points to the importance of 
tying/keying in the building to the foundation well, although I 
expect that the failure would then be the mortar in the stone 
foundation. Another interesting observation was the amount of 
shearing, probably at horizontal layers that were not tied together 
so well. Embedding bamboo dowels or something like this throughout 
the walls would greatly reduce this type of failure. I am not an 
engineer so we will have to await their report. The engineers however 
were very impressed by cob's performance and now have some good data 
and video footage to explore ways to increase cob's strength for 
those of us in earthquake zones.

At some point soon, we will try to get the video of the siesmic test 
up on the internet.

Ian Marcuse
Down To Earth Building Bee
www.stanleyparkcob.ca
www.alternatives.com/cob-building