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RE: Wood interior wall studs

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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(--nospam--at)cableone.net] 
Sent: Friday, July 13, 2007 12:16 PM
To: seaint(--nospam--at)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(--nospam--at)truesdellengineering.com>

	To: seaint(--nospam--at)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? 

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		*	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"... 

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		<!--[if !supportEmptyParas]--> <!--[endif]-->

		Andrew Heigley, PE

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		<!--[if !supportEmptyParas]--> <!--[endif]-->

		

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