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@poa02.usace.army.mil>
To: seaint@seaint.org
Sent: Fri, 13 Jul 2007 1:24 pm
Subject: RE: Wood interior wall studs
-----Original Message-----
From: Haan, Scott M POA <Scott.M.Haan@poa02.usace.army.mil>
To: seaint@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@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: <!--[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]--> ******* ****** ******* ******** ******* ******* ******* *** * Read list FAQ at: http://www.seaint.org/list_FAQ.asp * * This email was sent to you via Structural Engineers * Association of Southern California (SEAOSC) server. To * subscribe (no fee) or UnSubscribe, please go to: * * http://www.seaint.org/sealist1.asp * * Questions to seaint-ad@seaint.org. Remember, any email you * send to the list is public domain and may be re-posted * without your permission. 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