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GSBN: Digest for 6/9/07

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-> Re: GSBN: Wind loads and racking
     by Andrew Webb design@...


Date: 9 Jun 2007 21:29:41 -0500
From: Andrew Webb design@...
Subject: Re: GSBN: Wind loads and racking

Hi all,

Derek suggested I elaborate on this for the interest of the group.  This
engineer said "I do not need tensile ties through the bales but small
compressive ties just like the brick ties hold the bricks to a timber
frame."  My understanding of this analogy is that he wants something to
make the two leaves of render support each other as though the bales
were just an air space.  The thousands of straw stalks per square metre
that tie the the two sides of render together appear not to be enough
(for him).  His aim is to have a system that will pass the closest
scrutiny of the most conservative building certifier.  In that respect,
I guess he sees that he can calculate the strength of 9 pieces of 8
gauge wire (per square metre at 450 c/c), whereas he can't calculate the
strength of 100,000 to 200,000 pieces of straw.

This rationale appears to be totally flawed and I will re-read the
various reports and studies that many of you on this list have done
(once I'm past a major deadline for a different project).

Why am I pursuing this with this engineer?  Firstly, I have only just
started and if we reach an impasse I will go elsewhere.  But, I am
aiming to find a local engineer that I can work with on SB projects.
There are experienced engineers in Brisbane and in other states but
that's a long way away to go, particularly as I prefer face-to-face
design meetings and hate driving.  Also, building certifiers can be
reluctant to sign-off on inspections for SB buildings.  Inspections can
alternatively be done by an engineer so in that respect it is good to
have someone nearby, to keep costs down for clients and avoid the
engineer having to drive excessively.  This latter point makes this
engineer's aim a moot point as far as I can see, BTW.

Another aim of mine is to maintain the client's choice for compression
systems as much as possible.  There are several professionals from other
states who run training courses, many of them on this list, and they use
a variety of compression systems - John's all-thread @ 1800 c/c, Chris
and Colin's all-thread @ 900c/c, Frank's gripples and hi-tensile wire,
Iain's gripples and fencing wire, Brian's polyester strapping, etc.
(please forgive the simplification, it's just to illustrate the point).
They all have merit and all have potential problems.  I think the most
important thing for an owner-builder is to be confident in the technique
they will use to build their house and therefore it is important to be
able to use the system they have trained in.  If this latitude proves
not to be possible due to regional factors, then so be it, but at this
point there is no conclusive evidence against it.  (in fact every one of
these systems has been used here, as well as at least one house with no
compression whatsoever - one of the oldest ones circa 1996-8).

I am looking at all of the possibilities critically so that I can be
confident in the advice and detailing I provide my clients (which I was
until this engineer put his two cents in).

Back to the main point, I would be interested in more thoughts on this
through-tie issue.

All the best,

Andrew Webb wrote:
> In a strange but true development, the engineer in question has said
> that he doesn't want the through ties for tensile strength but for
> compressive strength, like brick ties

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