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RE: Renovation Help Wanted Again
- To: seaint(--nospam--at)seaint.org
- Subject: RE: Renovation Help Wanted Again
- From: IRV FRUCHTMAN <ifaeng(--nospam--at)yahoo.com>
- Date: Thu, 11 Nov 2010 17:27:46 -0800 (PST)
I'll take your advice about not changing anything.
--- On Wed, 11/10/10, Conrad Harrison <sch.tectonic(--nospam--at)bigpond.com> wrote:
From: Conrad Harrison <sch.tectonic(--nospam--at)bigpond.com>
Subject: RE: Renovation Help Wanted Again
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.