-----Original Message-----
From: Andy Heigley [mailto:aheigley@jgaeng.com]
Sent: Friday, July 13, 2007 12:46 PM
To: seaint@seaint.org
Subject: RE: Wood interior wall studs
Actually the 5 psf is due to HVAC.
Here's and excerpt from the IBC Handbook:
"According to BOCA/NBC, the requirements of this section, reproduced
from the 1999 BOCA/NBC section 1606.9, are intended to provide sufficient
strength and durability of the wall framing and wall finish, so that a
minimum level of resistance would be available to nominal impact loads that
commonly occur in the use of a facility and to HVAC pressurization."
Andrew Heigley, PE
-----Original Message-----
From: Haan, Scott M POA [mailto:Scott.M.Haan@poa02.usace.army.mil]
Sent: Friday, July 13, 2007 4:25 PM
To: seaint@seaint.org
Subject: RE: Wood interior wall studs
I think the 5 psf is intended for people slam dancing on the walls - not for
pressure from HVAC. The IBC has the 5 psf in the Live Load section. The 97
UBC says the 5 psf is "L" and does not need to be applied with wind or
seismic.
I would use the 1.15 Cr and 1.0 for Cd for the 5 psf.
-----Original Message-----
From: Joseph R. Grill [mailto:jrgrill@cableone.net]
Sent: Friday, July 13, 2007 12:16 PM
To: seaint@seaint.org
Subject: Re: Wood interior wall studs
There is also repetitive member increases in bending. 15% usually, but the
code allows 50% if a wind load.
Joe Grill
----- Original Message -----
From: Jordan Truesdell, PE <mailto:seaint1@truesdellengineering.com>
To: seaint@seaint.org
Sent: Friday, July 13, 2007 1:07 PM
Subject: Re: Wood interior wall studs
I do a lot of wood, and here's my take:
The 5psf should be at a Cd of 1.6. Why? Unless I have an
intentionally pressurized room (which is not the case here), there is no
possible way that common construction techniques can _maintain_ that kind of
pressure differential over an extended period of time, and if you have a
constant load (say, a commercial kitchen with doors that seal
tight...right...) making the pressure differential then the HVAC engineer
should already be providing makeup air in that area. The building code can
call it a "live" load all it wants, but the actual duration of load will
never reach 10 years in the 50 year design life of the building.
Roof live load should be given a Cd of 1.25; snow is 1.15.
I don't recommend a loadbearing wall of 10' in height be made of
2x4s. Why? Because the walls will not be sheathed before the floor joists are
set into place. The code limits the L/d ratio to 75 for construction, and a
10' 2x4 has an L/d of 80. The contractor cannot build the wall unless he
plans on bracing every stud without violating the code.
And, for the record, I agree with Don that 2x4s 10 feet long look a
lot like spaghetti. And as a bearing wall they give me the willies. My answer
to such a request is normally to do it as designed, or provide another PE to
seal off on the change with full calculations, and provide me with a full
release of liability should anything happen. I've never been taken up on the
offer.
Jordan
Andy Heigley wrote:
Everyone:
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Thanks for your responses...
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Here are my responses to some of your questions back:
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* I would design for LL and LLr if the wall were
supporting both the floor and roof loads.
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* I am designing to ASD.
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* I guess I'm a little leary of using the Cd of 1.6
for
this reason. The duration factor is applied to both bending and axial
capacities. Applying 60% more to the allowable axial stress makes a huge
difference. And if you have a 4 story building, for example, you are going
to be approaching the capacity of the stud just due to DL and LL... you then
add a "little bit" of short term horizontal loading to the stud and increase
the capacities by 60% seems non-conservative.
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* Scott: I haven't found the rated wall design
reduction factors you've mentioned. Can you tell me the code section that is
in?
<!--[if !supportEmptyParas]--> <!--[endif]-->
* 10'-0" high 2x4's... exactly why I initially called
for 2x6 stud walls, but the GC is flipping out about it... I get the old,
"I've been doing this for 30 years, and never had to do this before"...
<!--[if !supportEmptyParas]--> <!--[endif]-->
<!--[if !supportEmptyParas]--> <!--[endif]-->
Andrew Heigley, PE
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