Windloads for a building in a building

[Patukott]

Hello!

I have a building inside a building and am calculating the horizontal loads for global stability. Does anyone have any idea if and how large should the wind loads be? Right now I am going by the internal pressure coefficients in the eurocode. Technically they should cancel each other out for global stability as they pull the inner building in opposite directions. But I'm assuming there might be doors open on both sides of the outer building causing a draft inside. Although then it might not be appropriate to use the internal coefficients anymore.

 

[SteelPE]

That is an odd scenario. You could always design the inner building for the full wind as if the outer building wasn't there. Probably very conservative.

I worked on a project in the US 20 years ago with a similar situation. In this instance, I don't think we really checked the building for "wind" but rather seismic. In this instance, the inner building was heavily fortified and had a precast "roof" so it was quite heavy causing some decent loads the building needed to resist. In our jurisdiction seismic loads equals approx. 6% of the weight of the structure.

Come to think of it, I have designed a few independent cleanrooms using the same criteria..... although those structures were much lighter.

Does the Eurocode have some sort of minimum lateral load for internal partitions? The IBC requires a minimum load of 5psf for internal partitions over 6' in height.

 

[milkshakelake]

How open is the outer structure? Is it generally a normal enclosed building or is it something open like a parking garage?

 

[Lomarandil]

Yeah, I'd certainly set two lower limits of 5psf wind or 2% DL. Whether a higher load is appropriate depends a lot on the enclosure (and scale?) of the larger building

 

[milkshakelake]

Agreed with Lo. For a building within a standard building (nothing fancy or unusually open), we just use 5 psf wind load or basic integrity lateral loading, which might be 2% or something else in your code. I wouldn't cancel out the 5 psf on both sides like OP suggested because that's probably based on a building outside, where wind has free space to flow. I don't think that fully-cancelling-out condition ever happens in real life.

 

[HTURKAK]

....Right now I am going by the internal pressure coefficients in the eurocode...

You have two options ;

- Use the coefficients as per clause (7.2.9 Internal pressure , assuming interior walls ) considering the size and geometry of openings ,
- Conservatively assume the building is at outside .

 

[JAE]

Note that the 5 psf wind that Lomarandil and milkshakelake suggest is a service level force (i.e. there's no load factors on them).
ASCE 7 now lists that as 10 psf I believe as a factored load.

 

[Patukott]

Thank you for your replies!
I am taking 2% of the DL and LL as a horizontal load, the wind load would be on top of that.
The outer building itself is closed, it is an old industrial building that is being renovated and inside it are going to be built multiple two story high "boxes".
The idea of a wind load canceling itself out in global stability comes from this diagram in EN 1991-1-4. If the internal pressure is always either positive or negative on all internal surfaces, then for a box inside a building you would have opposite forces on either side of the box.

 

[isidor_]

I made a topic about this a few years ago, I got just about the same responses as you and I don't think there is any clear guidance in eurocode other than what have been suggested.

Lateral load structure within building - Structural engineering general discussion

Hi, (Eurocode applies where i work) Say i have a large building (large industrial building) and within it a smaller structure shall be built. How is the lateral load calculated for a structure within a building? There is ofcourse the unintended inclination that will affect the new smaller...

www.eng-tips.com

I designed my interior structure for the horizontal load corresponding to the interior wind pressure (0,3 or 0,2)*q_p. NOTE I used them on both sides of the interior structure and in the same direction so that they do not cancel each other out.

 

[human909]

For structures enclosed by other structures I generally don't explicitly design for wind loads at all. After all the structure is essentially not exposed to the wind so why design for it!**

For the structures I'm involved in it wouldn't at all be a dominant lateral load. **Of course if you are designing a very light wight air tight structure then internal pressures could become dominant.

My lateral system would be designed around seismic loads or in the case of dominant live loads a reasonable percentage of them. I keep deflections low and everybody is happy.

 

[Patukott]

I made a topic about this a few years ago, I got just about the same responses as you and I don't think there is any clear guidance in eurocode other than what have been suggested.

Lateral load structure within building - Structural engineering general discussion

Hi, (Eurocode applies where i work) Say i have a large building (large industrial building) and within it a smaller structure shall be built. How is the lateral load calculated for a structure within a building? There is ofcourse the unintended inclination that will affect the new smaller...

www.eng-tips.com

I designed my interior structure for the horizontal load corresponding to the interior wind pressure (0,3 or 0,2)*q_p. NOTE I used them on both sides of the interior structure and in the same direction so that they do not cancel each other out.

Yeah, I don't see any better guidance, although I wonder if there is anything about it in other codes.
Considering the Eurocode also gives this schematic then using both positive and internal pressure at the same time should be conservative for a wall/box inside a building that isn't fully splitting the space. I don't think it is correct to use only 0.3 or 0.2 on both sides as one is for pushing and the other suction. In this case you would have both, so one side would get 0.2 and the other 0.3

 

[EZBuilding]

Note that the 5 psf wind that Lomarandil and milkshakelake suggest is a service level force (i.e. there's no load factors on them).
ASCE 7 now lists that as 10 psf I believe as a factored load.

Jae do you have a reference in ASCE 7 for that? I still see that as a live load in 4.3.4

 

[jjl317]

I am pretty sure its actually in the IBC (in 2012) 1607.14 "Interior Walls and Partitions"

 

[JAE]

There's a "partition live load" that deals with the vertical dead weight of interior partitions. That was based on the ASCE 7 committee using a metal stud wall sheathed on both sides with gypsum board sheathing and spaced at 10 ft. o.c. getting you to 15 psf or so.

The lateral partition loading is indeed in the IBC as jj1317 states.

 

[phamENG]

The lateral partition loading is indeed in the IBC as jj1317 states.

It's also in ASCE 7-22 Chapter 4 (Live Loads)

 

[JAE]

Thanks pham. It wasn't included in my older 7-10 version and I don't have access today to the more current versions.