Wind Loads on Interior Walls 2

[PocketCalc]

If you were designing an interior freestanding architectural wall (separate from the overall building design), anchored to the building slab, would you design it for any specific wind loads for an IBC-based design? It's obvious that it would need to be designed for a minimum of 5 psf per IBC 2021 Section 1607.16 (if the wall exceeds 6 feet in height). However, the requirement reads that interior walls "shall have adequate strength and stiffness to resist the loads to which they are subjected but not less than a horizontal load of 5 psf". This is clearly a live load, in the Live Loads section of the code, and not a wind load, and it states that they may be other loads to which the wall is subjected. I've heard in the past that this can account for any incidental interior "wind". The commentary seems to support that the 5 psf is to account for loads due to changes in air pressure from air conditioning, small impacts, etc., but does not specifically mention wind.

It seems obvious on the face of it that a typical wall internal to a building would not need to be designed for full exterior wind loads as they are not exposed to significant winds. However, there are sections of the code that imply otherwise: In 1609.1, "Buildings, structures and parts thereof shall be designed to withstand the minimum wind loads prescribed herein. Decreases in wind loads shall not be made for the effect of shielding by other structures." There is no exception provided for interior walls. That at least leaves open the possibility of arguing that decreases can be made for the effect of shielding by the same structure, which I guess you could potentially argue since freestanding does not seem to be clearly defined in the code? ASCE 7-22 reads slightly differently, though; Chapter 29 covers wind loads on Building Appurtenances and Other Structures, which includes solid freestanding walls, and would seem to also include solid freestanding walls interior to a structure. In 29.1.4, "There shall be no reductions in velocity pressure caused by apparent shielding afforded by buildings and other structures or terrain features." This would seem to imply that a solid freestanding wall designed to be placed within a fully enclosed building would need to be designed for a full wind load as if the building weren't there. Can you argue that an interior wall doesn't need to be designed for wind, so there's nothing to reduce? It seems not: In 26.1.1, "Buildings and other structures, including the main wind force resisting system (MWFRS) and all components and cladding (C&C) thereof, shall be designed and constructed to resist the wind loads determined in accordance with Chapters 26 through 31." This seems to apply to ALL structures, and provides no exceptions for interior structures or structural components.

Now, it seems apparent to me that these sections generally relate to shielding of exterior structures from adjacent structures, but it would be nice to have some support to that point of view. I've pored over the IBC and ASCE 7, both codes and commentaries, and I can't find anything solid to support the view that interior walls need not be designed for a full wind load. The only real hint that I can find is that it seems fairly unnecessary to create a 5 psf minimum load on interior walls if all interior walls are supposed to be designed for minimum wind loads anyway. It certainly does not seem common practice to design interior walls for full wind loads, but I thought I would get some other opinions.

 

[jerseyshore]

I think you're looking too far into this IMO. If the wind is going to hit it, you design it for wind. If it's inside, you throw on 5 psf. If you have a partially open or open structure then you design those accordingly.

 

[GC_Hopi]

Yes generally interior does not get designed for the full wind load. ASCE 7-10 (28.4.4) and IBC 2012 (1609.6.3) had listed minimum wind pressures at 16 psf for walls. I would probably design for some incidental loading just to go beyond the code minimum (also known as idiot proof the design). Examples would be put railing load on the wall or the OSHA tie off load. What material is the wall?

 

[JAE]

I agree with above -- the interior walls only use the 5 psf (service) load and doesn't apply to exterior walls subjected to environmental wind loads.

But keep in mind that the code is a "minimum" standard. You, as the engineer, can use your wits and engineering judgement and decide if there's a valid reason for perhaps higher loads on your architectural wall...say a nearby series of overhead doors or something.

Always a good idea to keep your designs in a free, logical context and not just blindly rely on a code.

 

[PocketCalc]

Well, the problem is, it seems obvious to me, in that my colleagues and I design similar structures commonly without putting full wind loads on things. However, a particular code reviewer has brought up the question and I'm trying my best to come up with a response other than "You obviously don't design interior walls for full wind loads." I figured it would be fairly easy to find support for that point of view in the codes, but it's proving surprisingly difficult.

The wall is basically an aluminum box, with aluminum channels and tubes as internal supports. I am completely confident that 5 psf is adequate for the anything reasonable that will apply to this wall, and designing for a full wind load will make anchorage to the existing building slab untenable without having to cut out the existing slab and pour new foundations.

 

[driftLimiter]

This idea that the shielding clause of ASCE means all interior surfaces are subject to exterior wind pressure is missing the spirit of the wind chapters. There are very clear definitions of internal and external pressures, and enclosure classifications. This is where I believe the answer lies. If you have an internal pressure and the space is unpartitioned then the pressure acts on all surfaces of the wall and cancels. If the space is partitioned and there is an unbalanced pressure then you have some net wind load.

The Definitions and commentary on enclosure in ASCE 7-16 provides a more detailed point of view and discussion on unbalanced internal pressures.

 

[Aesur]

This reminds me of that video where a dad is asking his kids to write steps to make a sandwich and he follows it literally, they quickly find it's tough to write instructions to provide a 100% clear and precise method for building the sandwich and eating it. Code reviewers are starting to lose the ability to think outside what the code says, sadly our society is headed that way in general.

I would point out that other structures implies a separate building, and this wall is inside of and part of this building, therefore it doesn't see exterior wind loading. If they tried to argue back, I would elevate to the building official. If they still insisted, I would tell the client they are forcing me to design your interior walls as exterior for wind loading, they aren't willing to listen and let the owner argue it, they usually have the lawyers and funds to fix building departments.

 

[phamENG]

However, a particular code reviewer has brought up the question

What question, exactly? What is their precise comment/question?

In these cases, I usually try to turn it back on the reviewer. If their comment isn't clear, I push them for clarification. I let them spend the time making their case, and then poke enough holes in it to deflate it and move on. If they refused, I'd escalate to their supervisor complaining that their reviewer isn't providing clear comments, but haven't had to do that yet.

If you try to make your case against a vague comment, you may end up chasing your tail for 3 days when all you needed to do was to point them to a definition they misread.

 

[JStephen]

Some other thoughts:
-Generally, you don't apply wind loads to just one surface at a time, so if they apply wind loads to interior walls, they would logically be applied to all interior walls at the same time. So overall wind loading on the building would be 3-4 times higher, depending on the number of interior walls.
-All the wind loading diagrams in the codes always show wind acting on exterior surfaces only, which should be a pretty clear indication of the intent.
-If I remember right, ICBO does offer code interpretations. Not for the general public, but for building officials. So if it's not clear enough in the codes, the reviewer might wish to run it through that avenue. I would think a simple question would be quick to answer, but that may not be the case.

 

[GC_Hopi]

I agree with phamENG about asking for clarification. Sometimes it feels like the bureaucracy makes it difficult contact the reviewers. I had one review where reviewer went out of their way, if you could call it that, to put a statement to please call if any comments are unclear and put their direct number. I called the number and had a pleasant chat. The guy told what responses he wanted, I made some minor revisions on the drawings, and that was it. He said he was the only structural in his office so I think he was happy just to discuss structural items.

 

[ARPASEVAN]

For an architectural free standing wall, I also look into seismic loads if the finish is heavy such as stone on both sides shown below.

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