Non-building structures similar to buildings 4

[BAGW]

Hi,

As per ASCE, Industrial buildings qualify as non-building structures similar to buildings. Can Hangars qualify as non-building structures similar to building? Does ASCE specifically call out structures that fall under this category?

Thanks

 

[JAE]

I guess I see industrial buildings as....buildings.
Hangers are simply "buildings" as well. I think if you look in ASCE 7 under the non-building similar to building tables you get a feel for what they are talking about.


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[BAGW]

Aircraft Hangars can be classified as nonbuilding structures similar to buildings. Per ASCE, Buildings whose purpose is to enclose machinery/equipment, and whose occupant are engaged in maintenance of that equipment shall be permitted to be classified as nonbuilding structures.

 

[JStephen]

The "similar" is kind of deceptive, I think. I seem to remember seeing an example of a pipe rack that was considered "similar to buildings", meaning, in a structural sense, it's similar to a building, unlike, say, a tank, although not similar in appearance or function. I would assume a normal hangar was a building.

 

[IRstuff]

Seems to me that much rests on what this "hangar" actually does. The hangars I've been in consist of both aircraft spaces and office/lab spaces. There are some specialized hangars that contain only the plane and its support equipment, ala B2, which, to me, aren't even necessarily semi-permanent structures. I'm not sure how you could justify calling a 10-story structure a non-building.

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[BAGW]

@ IRstuff, Its a aircraft hangar housing just the plane.

I came across some explanation in structural engineer magazine, which states if the aircraft hangar is just used for maintenance of aircraft, it can be treated as a nonbuilding structure. See the attached link

http://www.structuremag.org/?p=11265

 

[MotorCity]

I have a hard time convincing myself that a hangar is not a building structure. For instance, say you classify it as a non-building because it is only used for aircraft maintenance. What if down the road, the building changes hands and is now used as a building to manufacture widgets. That means it now becomes a building? The decision to classify it as a building should be based on how similar its gravity and lateral systems are to a conventional building, not only what the building is used for.

 

[moltenmetal]

To an engineer who isn't a structural, the key here seems to be occupancy.

If the hangar encloses an aircraft and is only used to shelter crews maintaining the aircraft, then it's a nonbuilding structure.

Put a washroom/break room/supervisor's office in there for the mechanics and it's a building.

Same with a chemical plant: build a structural steel framework to support some pipe and vessels, and it's a non-building structure. Put a roof and cladding walls on it to keep out the wind and snow, it's still a nonbuilding structure. Put a lab, control room or other occupancy on it, it's now a building.

The trouble is, it seems there are people out there who think that anything with a roof and walls is a building, requiring all the protections intended for structures which are continuously rather than intermittently occupied. That drives up cost and complexity which often means that things that SHOULD be enclosed, are NOT enclosed merely to satisfy these rules. That isn't actually making things safer for workers one bit.

 

[BAGW]

Also, I had attended a seminar where they classified an Industrial building as a nonbuilding structure. The building was solely used for manufacturing purposes. I did not understand this until I found the paper I have posted in my previous post.

Any building used for limited occupancy can be classified as nonbuilding structure. So building manufacturing widgets can also be treated as nonbuilding structure.

 

[SwinnyGG]

What if down the road, the building changes hands and is now used as a building to manufacture widgets. That means it now becomes a building? The decision to classify it as a building should be based on how similar its gravity and lateral systems are to a conventional building, not only what the building is used for.

This scenario is no different than any other occupancy change a structure could be subject to- and it has the same effect with regard to code updates and and enforcement.

 

[MotorCity]

I understand that the occupancy plays into the classification as a building or non-building. The point I was trying to make is that it also depends on how the structure responds to seismic loads. The building's response during a seismic event does not depend on its occupancy, but rather the nature of its gravity and lateral systems. Look at a water tower. It has no occupancy, but it is a vital water supply structure. I would argue that its importance is at least that of an occupied building. Its response will be quite different than a typical building.

 

[JAE]

Well, there's non-building and non-building-similar-to-buildings. The commentary in ASCE 7 for chapter 15 discusses some things to watch out for in defining these two.

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[haynewp]

The hangars we deal with often have a lower admin area attached or immediately adjacent with an isolation joint, so collapse of the hangar could affect the admin portion of the building. We require it all to be designed as a building.

 

[Bagman2524]

IBC has two different classifications for hangers.
Occupancy U (Utility & Misc.): Aircraft hangers (for 1 or 2 family residence)
Occupancy S-1 (Storage - Group 1): Aircraft Repair Hangers

The fact that a building or structure could somewhere down the road be changed to a different occupancy use has no effect on the design of the building. If it does have a occupancy change then the proper procedures need to be followed for doing so, which would likely result in a reanalysis of the structure.

 

[JLNJ]

Maintenance and monitoring mean "nobody normally works in there" in my book. Most "industrial" buildings have people who work in them. It seems like a reasonable distinction.

That said, we should err on the side of life safety and not try to squeeze every dollar out of someone's initial construction cost.

 

[ATSE]

The statement: "The fact that a building or structure could somewhere down the road be changed to a different occupancy use has no effect on the design of the building" is technically true, but a little unrealistic and an otherwise pedantic argument. It is akin to designing a cantilever balcony for the minimum code load - the cost to add a 30% margin above the code minimum to flexural strength and waterproofing is pennies on the dollar, where failure is catastrophic.
I would be interested to know exactly how much budget is saved in materials by this non-building classification. If you know, please post that. Or is the motivation to expand the building heights per ASCE 7-10 Table 12.2-1?
A few examples of code minimum designs are below. Hopefully they were unoccupied.

 

[SwinnyGG]

The fact that a building or structure could somewhere down the road be changed to a different occupancy use has no effect on the design of the building" is technically true, but a little unrealistic and an otherwise pedantic argument

If this logic is taken to its end, every building would be built with the strongest, most robust, most durable techniques and materials available, for the most strenuous and dangerous occupancies, and the highest possible live loads. The side effect of this would be that no one would be able to afford to build anything.

You either respect the code, or you don't- you can't have it both ways just because there's a part of the code you don't like.

Ultimately, at some point in the process, the code must be interpreted by a human to determine whats appropriate and what isn't. This is why we are all able to pay our mortgages.

 

[ATSE]

jg,
I appreciated your perspective, but respectfully disagree. Most of the engineering we do considers (balances) reliability, total cost, and constructability. If a modification in design will cost 2% extra to the construction budget, but give 30% extra reliability for extreme events, this is a good bargain.
My point is not to specify stainless steel where mild steel is adequate. However, when an engineer attempts to interpret the code in a manner that is in dispute, or not generally accepted by his peers, and he believes this approach will save construction dollars, then it is reasonable to ask: Just how much savings are you achieving, how much extra future risk are you incurring, and also assigning to the life of the project. If you can't answer this with a decent confidence level, it is prudent to take the more accepted and slightly more conservative approach to the code.
This is particularly true of PEMBs.