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Re: Wood interior wall studs

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Let's put the 5 psf in perspective: it is only 0.035 psi or about 1" w.c., not unusual for an HVAC system. It likely would not occur, however, without the sheathing yet attached as there would be little to resist the pressure.
Regards,
Bill Cain, SE
Berkeley CA


-----Original Message-----
From: Haan, Scott M POA <Scott.M.Haan(--nospam--at)poa02.usace.army.mil>
To: seaint(--nospam--at)seaint.org
Sent: Fri, 13 Jul 2007 1:24 pm
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(--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:

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

        Thanks for your responses...

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

        Here are my responses to some of your questions back:

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

        *   I would design for LL and LLr if the wall were
supporting both the floor and roof loads. 

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

        *   I am designing to ASD. 

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

        *   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. 

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

        *   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

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

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

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

        

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