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GSBN: Digest for 6/18/07

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-> Re: GSBN: Wind loads and racking
     by jeff@...


Date: 18 Jun 2007 10:34:39 -0500
From: jeff@...
Subject: Re: GSBN: Wind loads and racking


I haven't piped up because designing specific buildings over email can
be dangerous, but a couple things to point out to your engineer are:

1.  If a frame is used, there are actually two compression systems -
plaster AND the frame.  The level of redundancy in compression is
usually off the map.  In fact, in some cases, the plaster has more
capacity than the columns in the frame.  Tying the skins together
increases the compressive capacity of the wall, but how much you
actually need should be determined first before making the decision to
do so.

2.  Failure in lateral tests is concentrated around the perimeter of the
panels, such as between the bales and sill plates, by the failure of
connectors such as staples or simply failure of the mesh itself.  The
boundary conditions are very important under lateral loads.  Tying the
skins together also increases the lateral capacity, but in many cases is
not necessary.  Also, the lateral tests in Bruce's book did not
incorporate a frame (columns).  One test not shown in Bruce's book (Cal
Poly) did incorporate columns that were anchored to the foundation with
hold-downs and used ties through the wall.  The results of that test
were much different than other tests without that type of boundary
condition and ties.  Even though this was only one test, it is worth
noting differences both in wall construction and results.

I am not going to say in general that tying the skins together is not
necessary.  It may be necessary in your situation, but what is important
to understand are the nature of the loads controlling the design and
what type of failure modes you are designing for.  Here in Colorado, we
have high winds and snow, but no earthquakes.  Depending on the plaster
material and building configuration, a level of reinforcement is
determined and connections to boundary members such as sills and columns
are specified based on the tests summarized in Bruce's book.  Since most
buildings have a frame system of some sort, compression is usually not
an issue, therefore tying the skins together is overkill in most cases
for us.  We have specified tying the skins together on one project.
That project was a grocery store in a seismically active area.  All of
our other projects outside of seismic areas do not require that level of
reinforcement simply due to the magnitude of the loads.

Finally, as an engineer who gets to design many bale structures each
year I feel that my exposure to risk is reduced with bale buildings
primarily due to the relatively high level of redundancy inherent in
these structures.  It is difficult to imagine catastrophic failure in
our region.  Basic common sense and paying attention to details will
suffice in most cases.  I like designing them because they are heavier
and usually stronger than framed walls.

Good luck,


- --
Jeff Ruppert, P.E.

Odisea LLC
Engineering and Consulting

Front Range Office 		West Slope Office
1731 15th St. #105		P.O. Box 1505 (mailing)
Boulder, CO  80302		337 Main Ave. (office)
303.443.4335			Paonia, CO 81428
303.443.4355 f			970.948.5744
jeff@...		1.866.795.6699 f


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