Load Duration for 5 PSF Interior Partition 4

[L_Bey]

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?

 

[JAE]

We've always treated it as a wind load.

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[DETstru]

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.

 

[Jerehmy]

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

 

[MrHershey]

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.

 

[TLHS]

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.

 

[JAE]

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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[XR250]

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

 

[Triangled]

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

 

[Jerehmy]

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.

 

[JAE]

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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[Triangled]

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.

 

[msquared48]

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)

 

[Triangled]

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

 

[msquared48]

Only in prisons...

Mike McCann, PE, SE (WA)

 

[L_Bey]

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.

 

[dik]

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

 

[Jerehmy]

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.

 

[dik]

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

 

[MrHershey]

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...