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Re: CBC 2007 Wind Load

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Title: Re: CBC 2007 Wind Load
I believe the code does not really differentiate between roof live load and roof snow load in that load combination (it has been a while since I specifically looked at it)...and considering that my normal “stomping” grounds is in snow country, snow load will govern just about ALWAYS over roof live load in my neck of the woods...and there can easily be snow/ice on the roof with high winds.

Beyond that, who ever said that EVERYTHING in the code is always 100% logical?  <grin>

Regards,

Scott
Adrian, MI


On 12/19/07 2:07 AM, "Gerard Madden, SE" <gmse4603(--nospam--at)gmail.com> wrote:

Who/what is on the roof causing live load during a wind event I ask?

-gm

On Dec 18, 2007 10:03 PM, Scott Maxwell <smaxwell(--nospam--at)umich.edu> wrote:
Conrad hit the nail on the head, I believe.  Depending on the building profile, there can be a downward wind force on roof members.  If this happens, then a D+L+Lr+W can be a controlling case for members carrying vertical loads (columns, footings, roof members, transfer members).

Regards,

Scott
Adrian, MI



On 12/18/07 8:25 PM, "Conrad Harrison" <sch.tectonic(--nospam--at)bigpond.com> wrote:

Not my code. But if roof live load is a gravity load, then in combination with wind down draft it may be a cautious combination to consider. But most of the time roof wind loads are uplift forces, so in combination with fictitious allowance for live loading that would be unconservative.
 
I've never done so to Australian code AS1170. But just checking it does have a combination, but involves a partial load factor of 1.2 for gravity loads. This infers a situation of wind down draft, or such situation that wind uplift in combination with the high estimate of gravity loads causes instability. Is there a partial loading pattern which would cause instability?
 
Turn the page, and partial load factor for live loading is zero for roof, unless used for floor like activities.

Regards
Conrad Harrison
B.Tech (mfg & mech), MIIE, gradTIEAust
mailto:sch.tectonic(--nospam--at)bigpond.com
Adelaide

South Australia


From: Gerard Madden, SE [mailto:gmse4603(--nospam--at)gmail.com] <mailto:gmse4603(--nospam--at)gmail.com%5D>  
Sent: Wednesday, 19 December 2007 11:18
To: seaint(--nospam--at)seaint.org
Subject: CBC 2007 Wind Load

The load combinations in ASCE 07 have combinations that combine Dead, Wind, and ROOF live load in the same combo.

While I can certainly see it being appropriate for floor live load to be combined with wind but not Roof Live and Wind simultaneously (even when reduced a little for each).

Possibly on primary frames/overall building (still hard to fathom in my opinion), but not for components and cladding (i.e. roof rafters).

Am I missing something?