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RE: Renovation Help Wanted Again

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I'll take your advice about not changing anything.

--- On Wed, 11/10/10, Conrad Harrison <sch.tectonic(--nospam--at)> wrote:

From: Conrad Harrison <sch.tectonic(--nospam--at)>
Subject: RE: Renovation Help Wanted Again
To: seaint(--nospam--at)
Date: Wednesday, November 10, 2010, 7:17 PM

Being near the ocean doesn't necessarily mean high wind loads. At ultimate strength limit wind speeds large waves are formed which increases the surface roughness decreasing the terrain category multiplier. Thus here whilst the automatic reponse would be to design for TC1 (Exposure D), we are permitted to design for TC2 (Exposure C), for strength. For serviceability check the wind speeds are lower and have less surface roughness increasing terrain category multiplier, so for serviceability use TC1 (Exposure D). This is explained in the Appendix to AS1170,2 and also in John Holmes book wind loading of structures. I don;t have ASCE7-05 with me to check if same apporach can be adopted. Plus most of dicussion on list seems to infer wind loading design in USA is serviceability level design, whilst here it is ultimate strength. So the approach may not provide any benefit.
When assessing existing I generally tend to try and get the loads as low as possible, and resistance as high as possible and otherwise avoid making any changes to the existing. If it has been performing satisfactorily why modify it.


Conrad Harrison

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



South Australia