Partition live load 1

[haynewp]

Should the 20psf parition load be included when calculating live load reductions? If not, why would codes define it as a live load? I am working off of IBC 2000.


When things are steep, remember to stay level-headed.
-Horace

 

[dik]

Partitions with the NBC of Canada are considered as DL and they have the requirement that 20 psf be considered for partitions other than permanent partitions. I normally don't consider them except as an added real load and stipulate on the drawings that "PARTITIONS SHOWN ARE FIXED PERMANENT PARTITIONS. NO ALTERATION, RELOCATION OR REMOVAL OF THESE SHALL BE MADE WITHOUT PRIOR APPROVAL OF THE ENGINEER"

So far no problems... Dik

 

[archeng59]

I don't include the 20 psf in the live load reduction calcs.

 

[dik]

Neither do I... by code, it is considered as a DL
Dik

 

[haynewp]

So then you would also use the dead load factor for design instead of the live load (LRFD) factor.

When things are steep, remember to stay level-headed.
-Horace

 

[haynewp]

In other words, you are still getting a break when you use factored design where I think I am supposed to be using full partition load and factoring it as a live load since it is listed under the live loads section.

When things are steep, remember to stay level-headed.
-Horace

 

[dik]

Sure... why not. Realizing that this is for fixed partitions. With CMU partitions you pick a heavier DL <G>. By code definition (in Canada), the partition load is dead load... (I agree, it makes about as much sense as 20 psf... ) In many instances, the area displaced by the wall system somewhat accommodates part of the weight of the partition. Not using my abacus, a 4-1/2 wall displaces about 18 lbs of a regular office space loading... which is about 1/3 of the weight of the wall.. It takes a lot of partitions to make up 20 psf... and even more if you consider the displaced area of floor loading. Using a reduced partition load only applies to fixed partitions and you stipulate that those shown are fixed as my earlier note; many office floors do not have a partition layout...

One of the firms I used to work with used to design offices for LL=65 psf and no partition load... the 65 psf closely mimicing the 20 psf partition.

Dik

 

[samdamon]

Haynewp-

For an office use, even though the code seems to say that the partition load is included within the live load when using > 80 psf LL, I treat it as a dead load and non-reducible. This is probably conservative but on balance I will have little control over what partitions are put in over the useful life of the building.

Believe that the statistical unlikelihood of actually ever getting a full live load on the floor is what drives the code to allow partitions to be included when designing with a higher live load. This is a nice idea in theory, but I think it is confusing in everyday practice. (The old BOCA had the this same issue as the current IBC does now).

For example, if partitions are moveable this means that corridor locations can change. Code minimum office live loads for corridors (100 psf first floor, 80 psf upper floors) are higher than for just office space (50 psf). I therefore usually end up designing the entire floor area that is going to carry moveable partitions for the corridor load. Doing anything else will restrict how that portion of the building can be used, imho.

So for example, for a non-composite steel framed first floor office, for gravity design I will use 80 psf as the reducible live load, but also add 20 psf to whatever the other dead loads are. I consider this as using the equivalent of a 100 psf IBC office live load. If you have composite beams then the 20 psf is a superimposed dead load after the concrete is in.

I still design using ASD most of the time, so haven't done this with LRFD load factors. But if I was, would probably use the lower DL factor for the 20 psf partition load.

The other question this raises is how do you treat the 20 psf moveable partition load when calculating mass for seismic loads? Have to admit I usually don't include it, which perhaps is inconsistent. Most of the buildings I work on are three stories max in low seismic risk areas, so there probably would not be a significant difference in the lateral shear if it was included. But for a much taller structure in a higher seismic zone the difference in lateral load could be huge. Any one out there who does tall buildings out west care to comment further?

The best practice might be to always include the 20 psf partition load as part of the seismic mass, but I know of nothing in the literature that justifies keeping it in or out.

Good question.

 

[OldPaperMaker]

In the 2003 IBC, Section 1617.5.1, indicates that the effective seismic weight shall include the total dead load and other loads listed below: #2 states that "Where an allowance for partition load is included in the floor design, the actual partition weight or a minimum weight of 10 psf of floor area, whichever is greater."

 

[samdamon]

oldpapermaker-

That provision is also in IBC 2000, which governs here. Thanks for pointing it out.

 

[haynewp]

sam:

I think the easiest thing to do is design the whole floor for the 80psf live load and make it reducible as you were mentioning. But I don't think I am going to go more conservative and add the 20psf to the dead load.

The reason for my decision on the 80psf reducible is that when I model the 50 + 20 in RAM, I have a hard time defining the 50psf office load as being reducible while making the 20psf live load partition irreducible.
If I enter the partition load in just as a dead load with 50 live, I have to make sure camber is not figured in for the partitions and I don't think I am meeting code if using LRFD by factoring the partition load as a dead load instead of as a live load (IBC 1607.5 seems to make partitions to be treated minimally the same as a 20psf Live Load, or the other option is to just use 80 psf "specified" live load (I am figuring this to be reducible).

IBC section 1607.9 references table 1607.1 for reducible live loads but does not mention 1607.5, therefore I think the 20psf partition load is not up for reduction. I will just use 80psf live load reducible for now on for the gravity only design plus whatever dead load there is excluding partitions.



When things are steep, remember to stay level-headed.
-Horace

 

[WillisV]

I'll give my shot at trying to clear things up - all references are to IBC 2006 but the ideas are the same for 00-03.

1. The requirements for a partition live load are for "office buildings and in other buildings where partitions are subject to change..." from 1607.5.

Therefore if it is known (such as say a condo) where all the partitions are (specifically located on the architectural drawings) then it is reasonable to treat the partition load as a known dead load - for typical construction the actual weight is generally in the range of 4-8psf but we generally use 10-15psf.

For offices etc. where the use can change then the 15psf (20psf in 00 and 03) should be a live load and the total live load would be 50+15 (50+20 in 00-03) or per 1607.5 a minimum of 81psf.

2. Which brings us to the second part - is the partition of the live load reducible? This is an interesting question so I got a code opinion from ICC. The summary: Yes it is.

"...Note that Section 1607.2 gives direction on live loads for uses not listed in Table 1607.1. Also note that Section 1607.3 requires design live loads to be the maximum expected by the intended use BUT NOT LESS THAN the minimum live load listed in the table. If Section 1607.9 is construed to mean ONLY the tabulated minimum uniform lives loads can be reduced, then a use that is not listed would not be eligible for a live load reduction. Similarly, where the actual design live load exceeds the minimum tabulated live load in accordance with Section 1607.3, a live load reduction would not be permitted. Such a narrow application of live load reductions would seem to be contrary to the rationale behind allowing live load reductions in the first place.

Section 1607.5 requires provision for partition weight under certain circumstances. This is accomplished by an additional uniform live load allowance, except where the design live load exceeds 80 psf. Accepting that Section 1607.9 should not limit reductions only to the minimum tabulated live loads for the reasons described above, it seems reasonable to permit reductions for the portion of the uniform floor live load which represents a partition allowance subject to the usual limitations in Section 1607.9.1 or 1607.9.2"

 

[haynewp]

OK, so their opinion is that 1607.9 applies universally to all live loads within the stipulations of that section (unless there is some specific case where using reductions would be completely irrational).

And therefore, 70 psf reducible could be used for a standard office building with no further regard for moveable partitions.


When things are steep, remember to stay level-headed.
-Horace

 

[WillisV]

Yes.

 

[miecz]

WillisV

Thanks for clearing that up. By repeatedly referring to Table 1607.1, Article 1607.9 seems to imply that only those loads are reducable.

 

[samdamon]

Sorry gents, I am confused now. Regarding the original question which prompted this thread, what might be the reasoning for the ICC to use a 20 psf "live load allowance" or a LL > 80 psf, (both reducible with Eq 16-1, they are claiming), for accounting for partition loads in gravity design, while using a different criteria (10 psf min or greater, not "reducible") for calculating the contribution of the same moveable partitions to seismic mass? Shouldn't the partition area loads used for gravity and seismic design be the same? Its that way for all the other dead loads we use.

The separate later question of what live loads are reducible per the IBC is also not cleared up. WillisV reports that the IBC opined that LL other than those listed in Table 1607.1 CAN be reduced. Or did I misunderstand the post? But Sect 1607.9 is clearly written to apply only to live loads in Table 1607.1, and even then there are caveats when using 100 psf LL or higher in certain cases. So if you are using a load outside of Table 1607.1 it doesn't seem clear if and how to reduce.

 

[WillisV]

1. The original question was can the 20psf partition live load be reduced and the answer is yes it can.

2. I believe the intent is that the 20psf (again reduced to 15 psf in IBC 2006) partition live load is used for gravity design for buildings in which the location of the partition walls is NOT known and this allowance is therefore meant to be able to cover the local conditions at the partition walls WHEREVER they occur realizing that in many places on the floor plate the true load will be 0psf and others it might be approaching 15-20psf.

The 10psf to be used for mass calculations realizes that the total mass of the walls is much much less than 20psf times the whole floor plate as this load was meant to cover the design of local conditions. This 10psf of "moveable mass" is meant to include the partition walls as well as furnature, file cabinets, etc. etc.

3. Yes from the ICC response live loads other than those listed in the table can be reduced however their statement was pointed to live loads for USES other than those listed in the table and it is not specifically written if and how to reduce but left up to the code official in the rather ambiguous statement of 1607.2: "For occupancies or uses not designated in Table 1607.1, the live load shall be determined in accordance with a method approved by the building official."

 

[dougantholz]

For gravity designs where you have the 20 psf partition load in your live load it is recible along side live load. For a good explination of actual loadings look at the commentary in ASCE 7. For instance we design office for an occupant live load minimum of 50 psf. Studies have shown that the average weight of office eqiupment plus occupants to be around 11 psf.

 

[samdamon]

For any interested there was a thread several years ago on this same set of topics at the Seaint server.

http://www.euken.com/group/seaoc/mailarchive/2003c/msg00965.html

If you follow the thread replies it is interesting to note that at that time an ICC official is quoted as saying that partition live load is not reducible (Albeit off the record). Regards

 

[JAE]

I've also heard that the 20 psf "partition" live load is a live load to account NOT so much for the partitions themselves, but rather to account for the fact that your 100 psf exit corridor locations will change with the relocation of the partitions and this would account for the higher LL capacity there.

I always couldn't figure out why they used 20 psf for partitions when I would calculate their weight at about 7 to 12 psf but the 100 psf corridor consideration made some sense.

I'd also second WillisV's explanations above.