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Load Duration for 5 PSF Interior Partition

Load Duration for 5 PSF Interior Partition

Load Duration for 5 PSF Interior Partition

(OP)
I'm designing an interior wood bearing wall to support 3 floors and a roof, as well as the standard horizontal load of 5 psf. The code does not specify exactly what this horizontal load is, and how it should be combined with other loads. Since this is a wood wall, the duration factor of the horizontal load also makes a significant difference in design. We've generally assumed that the horizontal load is to account for general internal pressure effects such as opening doors as well as any lateral loading from leaning on the wall.

If the interior wall load is treated as a transient load, and given a duration factor of 1.6 for a 10 minute duration, it would seem like it shouldn't apply in full combination with other live loads. But if it is combined at a 1.0 factor with floor live loads would the 1.6 duration factor still be correct for the stud design?

How have other people handled interior wood bearing walls with wall pressure?

RE: Load Duration for 5 PSF Interior Partition

I don't think I've ever seen the 5 psf interior wind pressure control a design so I typically ignore it for "normal" height walls.

The load combinations that include wind have a lower factor on the live load anyway. Couple that with the increased duration factor and it'll only control the design for a very, very tall wall.

RE: Load Duration for 5 PSF Interior Partition

The ASCE 7-10 specifies it as a notional load. In addition, the code gives you notional load combinations in 1.4.1.2 in ASCE 7-10.

a. D ± 0.7N
b. D + 0.75(0.7N) + 0.75L + 0.75(Lr or S or R)
c. 0.6D + 0.7N

RE: Load Duration for 5 PSF Interior Partition

I've always considered it a live load. For IBC 2009 it's specified in 1607.13. 1607 is the live loads portion of chapter 16.

RE: Load Duration for 5 PSF Interior Partition

Unless something very odd is happening, I normally use it to design the wall itself and the connections on the wall, and then just make sure there's a reasonable load path. I don't try to model it into the overall structural load.

The couple of times I've built something inside of something else, when it would govern lateral load, the lateral load on the system has looked so small that I've bumped it up anyway.

I don't use timber much, though, so don't have huge insight onto the duration factor to use off the top of my head.

RE: Load Duration for 5 PSF Interior Partition

The IBC actually has it in the Live Load section (1607.14 in IBC 2012).
We treat it as a wind load just because the only way a lateral 5 psf load could be applied to a wall seems to mainly be from differential wind pressures occurring within a space on either side of a wall.
I suppose it may also be due to people leaning on it, shelving, impacts, etc.

Jerehmy - can you identify where ASCE 7-10 calls it out as a notional load?

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RE: Load Duration for 5 PSF Interior Partition

The only time I use it is for interior metal stud wall and ceiling diaphragm design. I treat it as a wind load.

RE: Load Duration for 5 PSF Interior Partition

like JAE, we've looked at is as wind load

RE: Load Duration for 5 PSF Interior Partition

Jae-

In section 1.4 it states "... The effects of the structure and its components due to the forces stipulated in this section shall be taken as the notional load, N, and combined with effects of other loads in accordance with the load combinations of Section 1.4.1..."

Section 1.4.5 is the section that stipulates the 5 pounds per square foot pressure on wall for design of wall anchorage forces. As far as I know, this is the only location in the ASCE where the 5 psf wall load is mentioned. I understand it's for anchorage, but shouldn't the wall be able to resist these forces also?

I'm curious what older versions of ASCE have. I'll have to check tomorrow.

RE: Load Duration for 5 PSF Interior Partition

Jerehmy -
I see that - yes, it appears to only be talking about wall anchorage and ONLY when the wall provides "vertical load bearing or lateral shear resistance for a portion of the structure".
So this really doesn't deal with non-load bearing or non-shear walls like the IBC does in section 1607.14.

I beyer,
Per the IBC, then, it appears as a live load so your duration of load factor would appear to technically be 1.0 for wood.
However, per a recent thread I started, we were questioning the use of Cd = 1.0 for such "transitory" loads...suggesting instead the use of 1.10 or 1.15 as a sort of rationalization that some loads aren't as constant as more typical floor live loads.



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RE: Load Duration for 5 PSF Interior Partition

for what it's worth, the simpson connectors for interior walls to truss chords do not appear to allow short term duration increase. I may rethink my practice on this one.

RE: Load Duration for 5 PSF Interior Partition

Nominal wind load from doors opening and closing on all interior walls, regardless of the wall type. I never did use the 1.15 factor as it would not make that much difference in the result.

Mike McCann, PE, SE (WA)


RE: Load Duration for 5 PSF Interior Partition

does the phrase "climbing the walls" have relevance here?

RE: Load Duration for 5 PSF Interior Partition

Only in prisons...

Mike McCann, PE, SE (WA)


RE: Load Duration for 5 PSF Interior Partition

(OP)
I've never had a problem with treating the 5 spf as live load before, but I've got a stud that sees 4622 lbs (Dl+LL) compression and 54 lb-ft moment. It's also a 2x4 wall. It's slightly overstressed with both loads combined and a duration factor of 1.0.

RE: Load Duration for 5 PSF Interior Partition

Mike, only in prisons... about 40 years back I did some renovation work to Headingly Gaol, outside Winnipeg.

The entrance barrier was a huge steel barred wall with 1" dia bars at about 6" centres and horizontal steel straps every couple of feet... the bars passed through the straps and were welded... in addition, the bars had four lines of weld their length to prevent the straps from being forced down. The wall was approx 15' to 20' high (never measured).

The substantial wall was secured to the concrete slab above with three 1/2" dia lag bolts (don't know how long they were) in lead shields... just scratched my head and shook out the sawdust.

Dik

RE: Load Duration for 5 PSF Interior Partition

L. Beyer,

Did you apply any accidental eccentricity to that stud for the axial load? Breyer cites a reference that thinks 1" or 0.1d minimum should be used. I would definitely use minimum eccentricity for a column, but I'm not sure for a stud wall (probably).

My point being is having a slightly overstressed stud is a sightly different situation depending if you considered accidental eccentricity or not. I mean, 54 ft-lbs is not a big moment at all. A normal sized person can push with 50 pounds at mid wall easily causing 100ft-lbs moment in a stud.

RE: Load Duration for 5 PSF Interior Partition

I don't usually include for e values. Wall construction is normally symmetric about the middle and the added force to the wall due to the restrained height is small. A hundred pound wall with 1" eccentricity has an added load on an 8' wall of 100*1/96 = 1 pound... generally trivial. That the reason the minimal attachment in my anecdote above worked...

Dik

RE: Load Duration for 5 PSF Interior Partition

I would tend to not use a dynamic increase factor. Though difficult to imagine for the whole building, it's not difficult to imagine something putting out of plane load on a portion of wall or single stud for an extended period of time. Thinking like my garage where I have all sorts of stuff leaning up against the walls and hanging off the walls. I'm sure it's not anywhere near 5 psf of direct out of plan load, but it's something. NDS says two months for load duration factor of 1.15. That seems a bit optimistic for a lot of the crap hanging of the walls in my garage. Hell, the ten year duration given for a factor of 1.0 might be optimistic for some of it...

RE: Load Duration for 5 PSF Interior Partition

Dik...

Years ago I worked on the design of the prison in Monroe, wa. The walls were precast concrete, and all the connections had to be hidden. The connections were not as flimsy as you describe, but when you have all the time in the world, things do happen.

Mike McCann, PE, SE (WA)


RE: Load Duration for 5 PSF Interior Partition

I seem to recall one of Ron's comments... meaner than a junk yard dog that chews concrete... or something of that ilk.

Dik

RE: Load Duration for 5 PSF Interior Partition

L Beyer:
you may want to double check your stud capacity assuming you've got about a 9'4" stud height and 2x4 SPF#2 your allowable load would only be about 1,677 lbs considering the 5 psf as a live load and 2.0 duration factor.

We used to look at this as a internal wind pressure with Cd of 1.6 and have recently started considering it as a live load we found some commentary that is is there to capture incidental loads. I could see an argument that the wording of the 5 psf load in IBC makes it sound like in the absence of any other load it needs to carry 5 psf laterally not necessarily in tandem with the design loads, the clause seems to really be in place for non-load bearing partitions so someone leaning or bumping into them doesn't cause them to fall over.

http://files.engineering.com/getfile.aspx?folder=7...

RE: Load Duration for 5 PSF Interior Partition

We have the 2006 IBC commentary which states the following for Section 1607.13:

"The minimum lateral live load is intended to provide sufficient strength and durability of the wall framing and of the finished construction to provide a minimum level of resistance to nominal impacts that commonly occur in the use of a facility, such as impacts from moving furniture or equipment, as well as to resist HVAC pressurization."


Maybe this will help your decision on Cd.

RE: Load Duration for 5 PSF Interior Partition

(OP)
Celt83 - we're definitely using double studs for the bottom 2 floors - there's just no way to get the capacity we need in a 2x4 wall without. It was more of a question of have we considered the loads appropriately and do we need to drop the stud spacing as well.

RE: Load Duration for 5 PSF Interior Partition

Jerehmy:
We've used that commentary to rationalize Cd of 2.0 and treating it as full DL+LL and full lateral LL rather than using the 0.75 factor for two transient loads in the past.

L Beyer:
Gotcha we've had a few walls here that pushed to LSL's especially in the 5 story wood jobs that are getting more common, unless we can get buy in on 2x6 interior walls early.

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