[GSBN] PAKSBAB Straw Bale House Shake Table Tests - March 27, 2009 - A Great Success!
mfhammer at pacbell.net
Sat Apr 4 16:44:21 CDT 2009
I¹ll add a few things to Darcey¹s initial report about the PAKSBAB shake
The tests in the range of 1.50 to 2.00 times the Northridge earthquake were
quite dramatic. There was significant movement of the building (relative to
the table) and increasing damage to the plaster (new cracks, crack
enlargement, delamination of plaster in places) as the forces were increased
with each test. But the building as a whole did very well, and even at
twice the Northridge quake, did not ³fail² in the sense that there was no
structural failure. It¹s difficult to predict at what force it would have
suffered a collapse or failure of one or more structural elements.
I¹m not sure how it was decided to stop at twice the Northridge quake, but I
do think it was an appropriate stopping point. If for no other reason, it
allows repair of the building (by replacing damaged plaster) and retesting
it to see how it will fare after being repaired. This is very valuable
information, and there is a tentative plan to do so.
The last test did make many people nervous that another step might topple a
wall. This included the University professors who oversee the lab and its
testing. On a visceral level I was in that camp, but I suspect that was due
to the system¹s ability to move as much as it did (laterally and uplift),
but then come back to it¹s original place (more or less centered on the
foundation). So it looked like it might begin to fail, but then it rescued
The wall system includes nylon fishing net reinforcement that wraps under
the foundation and is embedded in the soil cement that encapsulates the
gravel bag foundation, continues and is embedded in the clay plaster on the
bales, and is attached to the lumber top plates. In the last few tests the
nylon net stretched and deformed in a few places at the foundation, but it
generally seemed to allow only so much drift and then pulled the wall system
back to a stable position. There was little or no failure at the connection
of the net to the top plate, nor at the connection of the light corrugated
steel roof to the top plates. The opposing bamboo pins, engaging the
foundation and the top plates, seemed to perform well in resisting the
out-of-plane forces in a flexible manner.
Because there was no evidence of failure of the nylon net or bamboo, I
believe the building could withstand significantly greater forces and still
remain safe (that is, not collapse). But the threshold we stopped at is
already a fairly high one, and we¹re very happy with the building¹s
The ground acceleration numbers Darcey gave (see below) are the best measure
I currently know for comparing the shake table movement and forces to
historical earthquakes. I need to better understand earthquake metrics
(especially the logarithmic Richter scale and how it relates to ground
acceleration, total energy, etc) and all the other factors involved before I
say more on this subject. I¹m sure Darcey will have a good summary about
this in the future.
I don¹t want to start an exhaustive dialogue about the tests at this time.
Darcey is certainly the primary person to present findings from the test and
I know she is preparing to leave for Pakistan, so she has little time now to
properly do so. But I wanted to add my initial observations that I thought
some might be interested in.
I also want to acknowledge Darcey¹s diligent and tireless effort (with help
from many others) in shepherding and being the driving force behind this
very successful testing project.
On 4/2/09 12:21 AM, "Darcey Donovan" <ecoengineering at gmail.com> wrote:
> Dear GSBN friends,
> I'm pleased to report that our straw bale house performed exceptionally well
> during the shake table tests at the University of Nevada, Reno, last Friday.
> The input motion was the Canoga Park Topanga Canyon record of the 1994
> Northridge, California earthquake, Mw 6.7. The house was subjected to
> increasing levels of seismic shaking, beginning at 25% of the recorded ground
> acceleration and increasing at 25% increments until failure. The house
> survived 0.82g (0.82 times the acceleration of gravity), twice the
> acceleration of the Canoga Park record. The Geological Survey of Pakistan
> estimates the 2005 Kashmir earthquake, Mw 7.6, to have had peak ground
> accelerations in the range of 0.3 to 0.6g.
> I am extremely grateful to EERI, NEES and UNR for their generous support, and
> to all the hardworking volunteers who dedicated countless hours to this
> To view the abstract and download a handout please go to
> http://nees.unr.edu/projects/straw_bale_house.html. See
> <http://www.kolotv.com/home/headlines/42035847.html> for publicity we¹ve
> received regarding the test. For more information about PAKSBAB please visit
> www.paksbab.org <http://www.paksbab.org/> .
> More videos and test report to come
> Kind regards,
> Darcey Donovan, P.E., C.E.O.
> Pakistan Straw Bale and Appropriate Building (PAKSBAB)
> P.O. Box 1083
> Truckee, CA 96160 USA
> (530) 902-5516 cell
> (530) 582-4965 fax
> 0344-9455664 PAK
> ecoengineering at gmail.com <mailto:ecoengr at sbcglobal.net>
> www.paksbab.org <http://www.paksbab.org/>
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