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RE: Open Builiding with mesh tarp roof - Ref. Air Permeable Cladd ing ASCE 7-05 6.4.3 and 6.5.2.2

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Thanks Conrad you perspective. The building has a simple gable roof with a slope of approximately 3v:12h.
 
Suresh Acharya, S.E.


From: Conrad Harrison [mailto:sch.tectonic(--nospam--at)bigpond.com]
Sent: Monday, May 12, 2008 11:54 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Open Builiding with mesh tarp roof - Ref. Air Permeable Cladding ASCE 7-05 6.4.3 and 6.5.2.2

If you use AS1170.2 there is reduction factor k[p] for permeable claddings also the Northern Territory (NT) planning department issued a notice with low pressure coefficients for structures covered with shade cloth. However, they require the shade cloth to be removed in strong winds. Most off-the-shelf canvas structures also require the structure is taken down in strong winds. There is a large difference between using the NT pressure coefficients and the results of using k[p]: I don't believe there is any experimental basis for either just some industry "pressure" to have something available.

 

AS1170.2 does provide internal pressure coefficients for various surfaces being semi-permeable. But other factors may come into consideration, for whilst an open trellis like wall may allow air to flow through, the drag loads on the individual slats may become significant. (Don't recollect seeing drag loads in ASCE7-05)

 

Also if it is residential owners go changing without approval. So simple pergola, no covering: gets shade cloth added, then much later gets steel roof cladding, and later still they enclose and turn into an extra room. Their problem until council tells them to apply for development approval or demolish: then it becomes my problem.

 

It is better to ignore the permeability, except in situations where it may increase internal pressure coefficients for a partially enclosed building: but ASCE7-05 doesn't provide much scope there.

 

Also what shape is a pliable fabric structure, with the wind blowing into it? The pressures being normal to the surface of a complex curved surface, formed by the action of the wind and stretch of the fabric. Have you considered the warp and weft of the fabric?

 

If looking at cable-nets and tension-membranes this may be useful:

 

http://www.arcaro.org/tension/

 

Regards

Conrad Harrison

B.Tech (mfg & mech), MIIE, gradTIEAust

mailto:sch.tectonic(--nospam--at)bigpond.com

Adelaide

South Australia


From: Acharya, Suresh [mailto:Suresh.Acharya(--nospam--at)ci.concord.ca.us]
Sent: Tuesday, 13 May 2008 05:04
To: 'seaint(--nospam--at)seaint.org'
Subject: Open Builiding with mesh tarp roof - Ref. Air Permeable Cladding ASCE 7-05 6.4.3 and 6.5.2.2

 

Any guidance for an open building with mesh tarp roof? ASCE 7-05 sections  6.4.3 and 6.5.2.2 apparently disallows reduction in wind pressures on air permeable cladding unless documented otherwise. And, these sections pertain to "cladding". I would assume, by extension,  MWFRS will also see no reduction due to holes.

 

 

 

Suresh Acharya, S.E.