[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

GSBN:Re: Wind loads and racking

I am confident that this engineer has put a lot of thought into this and
his concerns are justified.

I appreciate the politeness of your summation above, but I think the rest
of your message brings this into question.  While he may have put a lot of
thought into it, other parts of your message, and the worldwide SB
experience, suggest that his concerns are probably not properly calibrated
with the risks and benefits.  Most importantly, I concur with you, that his
proposed "solution" is expensive, inconvenient, likely to be ineffective
and to injure the workers.

I think a simpler, cheaper and much more effective solution is the welded
wire mesh, firmly attached to top and bottom plates, as used in
California's earthquake zones.  This method has the advantage of actual
testing.  I think you can find test information at the Ecological Building
Network site <<a  target="_blank" href="http://www.ecobuildnetwork.org/";>http://www.ecobuildnetwork.org/</a>>.  Thanks to Bruce King,
CASBA, and all others who supported that testing.  Bruce's new book, Design
of Straw Bale Buildings, also covers this and many other important SB
questions and techniques.  I think you've had some good tests done in
Australia, too.  If no one else has come up with the solution that your
engineer insists on, that is a pretty good hint that other options are
worth exploring (as you are doing).

Maybe some of the California seismic builders and authorities will chime in
here.  Best wishes,


Derek Roff
Language Learning Center
Ortega Hall 129, MSC03-2100
University of New Mexico
Albuquerque, NM 87131-0001
505/277-7368, fax 505/277-3885
Internet: derek@...

--On Friday, June 1, 2007 10:29 AM +1000 Andrew Webb
design@... wrote:

I am working with an structural engineer who has designed several SB
buildings and is insisting on an unusual detail that I have not seen
before.  Because of the potential cyclonic conditions here (sub-tropical
but cyclones can occur), he wants to ensure the two sides of render are
tied together to reliably ensure the wall acts as a sandwich panel to
resist lateral loads.  He proposes to put a grid of 8 gauge wires at 450
centres through the bales with the ends bent or looped to key into the
render, essentially like brick ties.  In so doing he assumes no lateral
resistance whatsoever from the bales, regardless of compression system
or pinning.  This detail also requires that the top and bottom plates
are fixed to the post and beam and floor structure, so that in itself is
not enough lateral restrain.

My concern is primarily practicality because:
1) it would be difficult to render, especially by hand, with these wires
sticking out.  Frequent puncture wounds
2) it would be hard to keep the wires from pushing in and out and moving
around while rendering and therefore to ensure they get embedded
properly in the render.
3) local cracking and ineffectiveness of the system
4) time consuming

One slight modification to improve 1 and 2 above would be to insert the
wires and bend them down after the brown coat is on, on both sides, and
before it dries.  3 would not be a big concern with cement render
(because it would adhere well to the steel), but I don't want to be
limited to that.

The extreme wind loading here is not that common in most of the SB
world; nor even in other parts of Australia where more SB buildings are
built.  I want to maintain flexibility of compression systems and
renders, basically clients' choice based on who they have trained with
(I'm an architect, not builder).  And, as I said, the engineer's concern
is regardless of compression system.

I am confident that this engineer has put a lot of thought into this and
his concerns are justified.  I also appreciate that he is trying to
achieve it as inexpensively as possible.  However, if we can reliably do
without the wires, with proof or come up with a better detail, I'd
prefer that.

Also, have there been any tests done on the racking resistance of SB

Any thoughts on this would be appreciated.

All the best,