Structural Engineering: 2007-07-08

Saturday, July 14, 2007

RE: Wood interior wall studs

I am not sure what provision you are referring to, but I believe the Cd factor applies in general to Fc. It does NOT apply to Fcperp.

Regards,

Scott

Adrian, MI

-----Original Message-----
From: Rich Lewis [mailto:seaint04@lewisengineering.com]
Sent: Saturday, July 14, 2007 8:48 PM
To: seaint@seaint.org
Subject: RE: Wood interior wall studs

Andrew,

You post has prompted quite a bit of good responses. I’m going to shoot from memory right now because I don’t have my NDS in this office. Regarding which Cd factor to use, I think you need to decide the actual time duration of the force and base your decision on the table given in the NDS. There is such a wide range of time durations and factors in the table. We know wood has a much higher strength for short load durations.

You made a statement below that prompted me to write this email. You stated “Applying 60% more to the allowable axial stress makes a huge difference.” I’m not sure if you are applying the NDS correctly. Once you have a slender element the Cd factor has very little influence on increasing the allowable axial load. I’m referring to ASD here. The Cd factor is only applied in the Cl & Cp factors. It is not multiplied by the resultant Fc value. It specifically states this in the NDS, but since I don’t have my copy here I can’t give you the reference. I have a spreadsheet I made for combined axial and bending. For a 9’-10” 2x4 stud I get an allowable axial stress of 397 psi for Cd=1.0 and 407 psi for Cd=1.6, using SP No. 2 wood. That is only a 2.5% increase in axial load. I just want to caution you since it does not appear anyone else questioned this statement.

Rich

From: Andy Heigley [mailto:aheigley@jgaeng.com]
Sent: Friday, July 13, 2007 2:39 PM
To: seaint@seaint.org
Subject: RE: Wood interior wall studs

Everyone:

Thanks for your responses…

Here are my responses to some of your questions back:

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

I am designing to ASD.

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.

Scott: I haven’t found the rated wall design reduction factors you’ve mentioned. Can you tell me the code section that is in?

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”…

Andrew Heigley, PE

You post has prompted quite a bit of good responses. I’m going to shoot from memory right now because I don’t have my NDS in this office. Regarding which Cd factor to use, I think you need to decide the actual time duration of the force and base your decision on the table given in the NDS. There is such a wide range of time durations and factors in the table. We know wood has a much higher strength for short load durations.

You made a statement below that prompted me to write this email. You stated “Applying 60% more to the allowable axial stress makes a huge difference.” I’m not sure if you are applying the NDS correctly. Once you have a slender element the Cd factor has very little influence on increasing the allowable axial load. I’m referring to ASD here. The Cd factor is only applied in the Cl & Cp factors. It is not multiplied by the resultant Fc value. It specifically states this in the NDS, but since I don’t have my copy here I can’t give you the reference. I have a spreadsheet I made for combined axial and bending. For a 9’-10” 2x4 stud I get an allowable axial stress of 397 psi for Cd=1.0 and 407 psi for Cd=1.6, using SP No. 2 wood. That is only a 2.5% increase in axial load. I just want to caution you since it does not appear anyone else questioned this statement.

Rich

From: Andy Heigley [mailto:aheigley@jgaeng.com]
Sent: Friday, July 13, 2007 2:39 PM
To: seaint@seaint.org
Subject: RE: Wood interior wall studs

Everyone:

Thanks for your responses…

Here are my responses to some of your questions back:

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

I am designing to ASD.

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.

Scott: I haven’t found the rated wall design reduction factors you’ve mentioned. Can you tell me the code section that is in?

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”…

Andrew Heigley, PE

Re: Enercalc, again

In a message dated 7/12/2007 8:08:18 AM Pacific Daylight Time, khemmatyar@gmail.com writes:

Dear Raj:

My personal and long term experience with ENERCALC and Michael Brooks, SE has been always VERY pleasant.

If you've noticed in the software literature, he recommends that users use email as the primary means of communication.

I believe based on the low cost of the software, simplicity of use, comprehensive multiple applications of ENERCALC, it will continue to be the one of the top software tools for simple tasks, used in the majority of Structural firms that I know Western United States.

I'd recommend that you send them another email, but use a non-Yahoo account! It does happen to all of us that some emails, end up in our junk mail box and yours seem to be one

I agree 100%

Antonio S. Luisoni

Consulting SE

Get a sneak peak of the all-new AOL.com.

Re: Wood interior wall studs

> From: "Jason Christensen" <jason.christensen@wcaeng.com>

> We usually call out mid-height blocking to be installed as the wall is
> erected, since it is usually the y-axis controlling, the blocking will
> drop your Le/d so the x-axis would control.

Two studs or a row of studs blocked together only enforce that they will
buckle in unison at the critical axial load if it is uniformly applied to
all studs. The bracing shear has to be resisted at the blocking elevation to
get a truly braced behaviour.

Regards
Paul
--
Paul Ransom, P.Eng.
ad026@hwcn.org

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Re: hss post weld on caps

I don't know if this is the answer, but you might try the Julius Bloom
catalogue.
Gary

Christopher Banbury wrote:
>
> I am looking for a supplier of steel weld-on caps for outdoor hss
> stair and railing posts.
>
> I recall seeing such caps on various projects but I'm not sure if they
> are shop fabricated or if they are a manufactured accessory.
>
> The caps I'm thinking of are a nearly flat pyramid with a small
> overhang that covers the end of the tube to keep out water and provide
> an architectural finish.
>
> Wagner has something similar but I think they are press-on not weld-on.
>
> Thanks all.
>
> Christopher Banbury, PE
>
> President
>
> Ark Engineering, Inc.
>
> PO Box 10129, Brooksville, FL 34603
>
> 22 North Broad ST, Brooksville, FL 34601
>
> Phone: (352) 754-2424
>
> Fax: (352) 754-2412
>
> www.arkengineering.net <http://www.arkengineering.net>
>
> <http://usa.autodesk.com/adsk/servlet/mform?id=9131297&siteID=123112&CMP=ILC-GN9219645015>
>

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Friday, July 13, 2007

Re: Spectral Acceleration using 2006 IBC

Be carful in how you use the USGS web site. If you
get to the right location it explicitly states that
the values are for the 2006 IBC. I initially used one
of the other options and got different accelerations.
If you are using the USGS website correctly you never
even have to think about whether it is 10% or 2%.

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Re: Spectral Acceleration using 2006 IBC

Larry-

The seismic design accelerations under the IBC 2006 are based on a "Maximum Considered Earthquake" with a mean recurrence interval of 2,500 years (2% in 50 years). The code then has you reduce the load to 2/3 of that value for the design basis loads which approximates a 500 year mean recurrence interval (10% in 50 years). In California near major faults, however, you need to be careful because the 500 year events can approach the deterministically limited motion on a given fault. But I guess we don't have to worry about that until 1-1-08 when the IBC2006, as amended, becomes the California Building Code.
Regards,
Bill Cain, SE
Berkeley CA

-----Original Message-----
From: Larry Hauer <lrhauer@hotmail.com>
To: seaint@seaint.org
Sent: Fri, 13 Jul 2007 3:03 pm
Subject: Spectral Acceleration using 2006 IBC

To get the long and short spectral accelerations for designing earthquake forces I have gone to the USGS website with the required latitude and longitude. However, the website lists 2 values for each, a 10%PE in 50 yrs. and a 2%PE in 50 years. Which of these sets of values am I to use when designing to the 2006 IBC?

Thanks in Advance,

Larry Hauer S.E.

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Re: Wood interior wall studs

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

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. Make sure you visit our web * site at: http://www.seaint.org ******* ****** ****** ****** ******* ****** ****** ********    ******* ****** ******* ******** ******* ******* ******* *** *   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. Make sure you visit our web  *   site at: http://www.seaint.org  ******* ****** ****** ****** ******* ****** ****** ********

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RE: Spectral Acceleration using 2006 IBC

That is correct. Larry's original question was with regard to the values
from the USGS website. The mapped spectral accelerations are typically
values at MCE which need to be adjusted for the site-soil conditions:
S_ms = Fa Ss
S_m1 = Fv S1
Therefore, design spectral response is 2/3 of those values.

David A. Topete, SE

-----Original Message-----
From: John Atilano [mailto:jatilano@laneengineers.com]
Sent: Friday, July 13, 2007 3:41 PM
To: seaint@seaint.org
Subject: RE: Spectral Acceleration using 2006 IBC

I thought we were to use the 2%POE in 50 years since it is the max
considered earthquake. The design is then 2/3 of the MCE which is the
reason for the equations Sds=2/3*Sms and Sd1=2/3*Sm1

John Atilano, P.E.

-----Original Message-----
From: David Topete [mailto:dtopete@gfdseng.com]
Sent: Friday, July 13, 2007 3:10 PM
To: seaint@seaint.org
Subject: RE: Spectral Acceleration using 2006 IBC

I believe the 10%POE in 50 years ( = 475 yr return period) is your
design
earthquake. The 2% in 50 is the Max considered earthquake.
The design is 2/3 of MCE.

David A. Topete, SE
-----Original Message-----
From: Larry Hauer [mailto:lrhauer@hotmail.com]
Sent: Friday, July 13, 2007 3:03 PM
To: seaint@seaint.org
Subject: Spectral Acceleration using 2006 IBC

Thanks in Advance,

Larry Hauer S.E.

_________________________________________________________________
http://imagine-windowslive.com/hotmail/?locale=en-us&ocid=TXT_TAGHM_migr
atio
n_HM_mini_2G_0507

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RE: Spectral Acceleration using 2006 IBC

I thought we were to use the 2%POE in 50 years since it is the max
considered earthquake. The design is then 2/3 of the MCE which is the
reason for the equations Sds=2/3*Sms and Sd1=2/3*Sm1

John Atilano, P.E.

-----Original Message-----
From: David Topete [mailto:dtopete@gfdseng.com]
Sent: Friday, July 13, 2007 3:10 PM
To: seaint@seaint.org
Subject: RE: Spectral Acceleration using 2006 IBC

I believe the 10%POE in 50 years ( = 475 yr return period) is your
design
earthquake. The 2% in 50 is the Max considered earthquake.
The design is 2/3 of MCE.

David A. Topete, SE
-----Original Message-----
From: Larry Hauer [mailto:lrhauer@hotmail.com]
Sent: Friday, July 13, 2007 3:03 PM
To: seaint@seaint.org
Subject: Spectral Acceleration using 2006 IBC

Thanks in Advance,

Larry Hauer S.E.

_________________________________________________________________
http://imagine-windowslive.com/hotmail/?locale=en-us&ocid=TXT_TAGHM_migr
atio
n_HM_mini_2G_0507

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Wall deflection

For interior walls the code limits deflection to L/120 and L/240. Is there a requirement for L/180 anywhere?

Mark E. Deardorff, SE
R & S Tavares Associates, Inc
9815 Carroll Canyon Road
Suite 206
San Diego, CA 92131
Phone: 858-444-3344
Phone: 209-863-8928
Cell: 209-765-5592
mark@rstavares.com
www.rstavares.com

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RE: Wood interior wall studs

We usually call out mid-height blocking to be installed as the wall is erected, since it is usually the y-axis controlling, the blocking will drop your Le/d so the x-axis would control.

Jason

-----Original Message-----
From: Donald Bruckman [mailto:bruckmandesign@verizon.net]
Sent: Friday, July 13, 2007 4:10 PM
To: seaint@seaint.org
Subject: RE: Wood interior wall studs

Sure is. Thanks for that….

So I guess that mean a note needs to be added to the drawings that shoring would be required? But once I get into that, what do I do with all the legal stuff from the AIA and their admonitions about not getting involved with “means and methods” of construction. Next thing the GC will ask for a shoring detail. Who wants into THAT can of slippery slope?

Interesting quandary.

I think I’d have to stand firm and just veto the 2x4x10 altogether. Bad detail anyway.

From: Jason Christensen [mailto:jason.christensen@wcaeng.com]
Sent: Friday, July 13, 2007 2:48 PM
To: seaint@seaint.org
Subject: RE: Wood interior wall studs

For solid sawn columns, Le/d shall not exceed 75, comes from NDS section 3.7.1.4, I am looking at the 2005 edition.

Jason

-----Original Message-----
From: Donald Bruckman [mailto:bruckmandesign@verizon.net]
Sent: Friday, July 13, 2007 2:25 PM
To: seaint@seaint.org
Subject: RE: Wood interior wall studs

The code limits l/d during construction? Whoa….where is that found?

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.

***** ****** ******* ****** ****** ********

RE: Wood interior wall studs

Sure is. Thanks for that….

Interesting quandary.

I think I’d have to stand firm and just veto the 2x4x10 altogether. Bad detail anyway.

From: Jason Christensen [mailto:jason.christensen@wcaeng.com]
Sent: Friday, July 13, 2007 2:48 PM
To: seaint@seaint.org
Subject: RE: Wood interior wall studs

For solid sawn columns, Le/d shall not exceed 75, comes from NDS section 3.7.1.4, I am looking at the 2005 edition.

Jason

-----Original Message-----
From: Donald Bruckman [mailto:bruckmandesign@verizon.net]
Sent: Friday, July 13, 2007 2:25 PM
To: seaint@seaint.org
Subject: RE: Wood interior wall studs

The code limits l/d during construction? Whoa….where is that found?

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.

***** ****** ******* ****** ****** ********

RE: Spectral Acceleration using 2006 IBC

I believe the 10%POE in 50 years ( = 475 yr return period) is your design
earthquake. The 2% in 50 is the Max considered earthquake.
The design is 2/3 of MCE.

David A. Topete, SE
-----Original Message-----
From: Larry Hauer [mailto:lrhauer@hotmail.com]
Sent: Friday, July 13, 2007 3:03 PM
To: seaint@seaint.org
Subject: Spectral Acceleration using 2006 IBC

Thanks in Advance,

Larry Hauer S.E.

_________________________________________________________________
http://imagine-windowslive.com/hotmail/?locale=en-us&ocid=TXT_TAGHM_migratio
n_HM_mini_2G_0507

******* ****** ****** ****** ******* ****** ****** ********

Spectral Acceleration using 2006 IBC

Thanks in Advance,

Larry Hauer S.E.

_________________________________________________________________
http://imagine-windowslive.com/hotmail/?locale=en-us&ocid=TXT_TAGHM_migration_HM_mini_2G_0507

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RE: Two-way flat plate hairline cracks radiating from columns

1951. The plans say to use deformed bars.

-----Original Message-----
From: Stuart, Matthew [mailto:mstuart@schoordepalma.com]
Sent: Friday, July 13, 2007 1:43 PM
To: seaint@seaint.org
Subject: RE: Two-way flat plate hairline cracks radiating from columns

Sounds like an old SMI slab. Are there concentric smooth round bars also?
How old is the structure?

Matthew Stuart

________________________________

From: Haan, Scott M POA [mailto:Scott.M.Haan@poa02.usace.army.mil]
Sent: Fri 7/13/2007 4:46 PM
To: seaint@seaint.org
Subject: Two-way flat plate hairline cracks radiating from columns

I had to go look at an old building where they are removing asbestos floor
tiles. They had sand blasted the floor on one level.

On each level there were cracks in the top of the floor slabs radiating
outward a few feet from columns. The building was constructed with only top
steel over the columns and with five dog leg shear rebars over the columns
each way. The slab was 12" thick.

Most of the cracks were hair line on the levels without sand blasting, none
were more than 1/16". On the sandblasted level the cracks were more
pronounced because the edges got rounded. There was no cracking visible from
the bottom of the slabs. The inspectors were alarmed by these sandblasted
cracks.

It appeared to me the cracking was from bending over the columns but that the
reinforcement was limiting the size of the cracks. It is not what I would
expect from a punching shear failure from looking at text books, but I was
thinking about how one of my college professors told me thin ice behaves when
you fall through and this looks like the picture he drew - cracks going every
direction from where your standing.

Any thoughts?

RE: Wood interior wall studs

For solid sawn columns, Le/d shall not exceed 75, comes from NDS section 3.7.1.4, I am looking at the 2005 edition.

Jason

-----Original Message-----
From: Donald Bruckman [mailto:bruckmandesign@verizon.net]
Sent: Friday, July 13, 2007 2:25 PM
To: seaint@seaint.org
Subject: RE: Wood interior wall studs

The code limits l/d during construction? Whoa….where is that found?

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.

***** ****** ******* ****** ****** ********

RE: Two-way flat plate hairline cracks radiating from columns

Sounds like an old SMI slab. Are there concentric smooth round bars also? How old is the structure?

Matthew Stuart

________________________________

From: Haan, Scott M POA [mailto:Scott.M.Haan@poa02.usace.army.mil]
Sent: Fri 7/13/2007 4:46 PM
To: seaint@seaint.org
Subject: Two-way flat plate hairline cracks radiating from columns

I had to go look at an old building where they are removing asbestos floor
tiles. They had sand blasted the floor on one level.

Any thoughts?

RE: Wood interior wall studs

Andy -
I think you are giving the load duration factor too much credit. For normal
height walls (8' to 12'), a Cd of 1.6 only increases F'c by 5% to 20% over
that of Cd=1.0. The increase in the allowable stress is a function of le/d,
so it is less for taller walls.

I like the discussion you've started though, I usually use Cd of 1.3 with
the 5 psf lateral load and use the same load combinations you listed in your
original email.

Josh Comfort, P.E.
Golden, Graper & Burton, Inc.
1500 W. Fourth Ave., Suite 509
Spokane, WA 99204
(509)624-3224 (509)624-3225 Fax

-----Original Message-----
From: Andy Heigley [mailto:aheigley@jgaeng.com]
Sent: Friday, July 13, 2007 2:14 PM
To: seaint@seaint.org
Subject: RE: Wood interior wall studs

True.

But talking about impact loading, that has a duration factor of Cd = 2.0.

I like this discussion, and how it applies to the 2x4 studs. Let's face it,
if it is 2x6 studs it doesn't really matter unless you're dealing with the
same slenderness ratios.

By the way, not that it helps much but my stud height is just less than 10'
at 9'-10".

I understand the reasoning for the 5 psf lateral loading. It makes sense to
have a provision for impact and internal pressure loads. It would be
wonderful if we could come to a consensus on how it is applied in wood
design and the application of the duration factor.

Let's say you have a 4-story building... it is primarily supporting axial
load. Let's say you are at 0.99 interaction ratio for axial loads only.
You then apply a minor out of plane bending load. If you then increase your
allowable stresses by 60% then your interaction is going to drop lower
significantly, when generally combined bending and axial result in worse
interaction ratio.

I'm starting to think that what might be more reasonable is if you use the
load Combination of DL + .75L + .75(out of plane live loading), with a Cd of
1.0. Or Design for 100% (DL + LL + out of plane) and a Cd of 1.6

What are people's thoughts on this?

And slam dancing = nominal impact loads.

-----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:

Thanks for your responses...

Here are my responses to some of your questions back:

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

* I am designing to ASD.

* 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.

* Scott: I haven't found the rated wall design
reduction factors you've mentioned. Can you tell me the code section that
is
in?

* 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"...

Andrew Heigley, PE

******* ****** ******* ******** ******* ******* ******* *** * Read
list FAQ at: http://www.seaint.org/list_FAQ.asp * * This email was sent to
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********

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RE: Wood interior wall studs

The formula for Cd for this situation is that if you are working for the
owner Cd=1.0 and if you are working for the contractor Cd=2.0.

-----Original Message-----
From: Andy Heigley [mailto:aheigley@jgaeng.com]
Sent: Friday, July 13, 2007 1:14 PM
To: seaint@seaint.org
Subject: RE: Wood interior wall studs

True.

But talking about impact loading, that has a duration factor of Cd = 2.0.

I like this discussion, and how it applies to the 2x4 studs. Let's face it,
if it is 2x6 studs it doesn't really matter unless you're dealing with the
same slenderness ratios.

By the way, not that it helps much but my stud height is just less than 10'
at 9'-10".

I understand the reasoning for the 5 psf lateral loading. It makes sense to
have a provision for impact and internal pressure loads. It would be
wonderful if we could come to a consensus on how it is applied in wood design
and the application of the duration factor.

What are people's thoughts on this?

And slam dancing = nominal impact loads.

-----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:

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 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:

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:

Thanks for your responses...

Here are my responses to some of your questions back:

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

* I am designing to ASD.

* 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.

* Scott: I haven't found the rated wall design
reduction factors you've mentioned. Can you tell me the code section that is
in?

* 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"...

Andrew Heigley, PE

******* ****** ****** ****** ******* ****** ****** ********

Re: Wood interior wall studs

Donald says it may be for cabinets and hanging loads. That may be construed
as long term. That would be a .9 factor. We've run the entire range now.

Sorry folks, but I've been through this discussion before.

Joe

----- Original Message -----
From: "Andy Heigley" <aheigley@jgaeng.com>
To: <seaint@seaint.org>
Sent: Friday, July 13, 2007 2:14 PM
Subject: RE: Wood interior wall studs

> True.
>
> But talking about impact loading, that has a duration factor of Cd = 2.0.
>
> I like this discussion, and how it applies to the 2x4 studs. Let's face
> it,
> if it is 2x6 studs it doesn't really matter unless you're dealing with the
> same slenderness ratios.
>
> By the way, not that it helps much but my stud height is just less than
> 10'
> at 9'-10".
>
> I understand the reasoning for the 5 psf lateral loading. It makes sense
> to
> have a provision for impact and internal pressure loads. It would be
> wonderful if we could come to a consensus on how it is applied in wood
> design and the application of the duration factor.
>
> Let's say you have a 4-story building... it is primarily supporting axial
> load. Let's say you are at 0.99 interaction ratio for axial loads only.
> You then apply a minor out of plane bending load. If you then increase
> your
> allowable stresses by 60% then your interaction is going to drop lower
> significantly, when generally combined bending and axial result in worse
> interaction ratio.
>
> I'm starting to think that what might be more reasonable is if you use the
> load Combination of DL + .75L + .75(out of plane live loading), with a Cd
> of
> 1.0. Or Design for 100% (DL + LL + out of plane) and a Cd of 1.6
>
> What are people's thoughts on this?
>
> And slam dancing = nominal impact loads.
>
> -----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:
>
>  
>
> Thanks for your responses...
>
>  
>
> Here are my responses to some of your questions back:
>
>  
>
> * I would design for LL and LLr if the wall were
> supporting both the floor and roof loads.
>
>  
>
> * I am designing to ASD.
>
>  
>
> * 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.
>
>  
>
> * Scott: I haven't found the rated wall design
> reduction factors you've mentioned. Can you tell me the code section that
> is
> in?
>
>  
>
> * 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"...
>
>  
>
>  
>
> Andrew Heigley, PE
>
>  
>
>  
>
>  
>
>
>
> ******* ****** ******* ******** ******* ******* ******* *** * 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. Make sure you visit our web * site
> at:
> http://www.seaint.org ******* ****** ****** ****** ******* ****** ******
> ********
>
>
> ******* ****** ******* ******** ******* ******* ******* ***
> * 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
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> * Questions to seaint-ad@seaint.org. Remember, any email you
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> * without your permission. Make sure you visit our web
> * site at: http://www.seaint.org
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>
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> * This email was sent to you via Structural Engineers
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