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GSBN:Wind loads and racking
- To: GSBN GSBN@...
- Subject: GSBN:Wind loads and racking
- From: Andrew Webb design@...
- Date: Fri, 01 Jun 2007 10:29:13 +1000
- Reply-to: "GSBN" GSBN@...
- Sender: "GSBN" GSBN@...
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
Also, have there been any tests done on the racking resistance of SB walls?
Any thoughts on this would be appreciated.
All the best,