ASCE 7 - What is the definition of "area" 2

[dengebre]

ASCE 7 now states that a wind importance factor of 1.15 must be used for “buildings where more than 300 people congregate in one area”. Previous editions stated 1.15 for “buildings where more than 300 people congregate in one room”. What is the definition of an “area”? A lot, building, floor or room?!

The Commentary for ASCE 7 provides some clarification in that it states the above applies to buildings designed for public assembly. However, the same sentence also states for “structures that have large numbers of occupants”. It seems the use of the term “area” is somewhat vague.

I would appreciate hearing how others have addressed this ambiguity. Thank you.

 

[MiketheEngineer]

Does it really matter?? I always figured if you can get 300 people into a building (room, area, hallway, whatever) then use an I of 1.15 for the whole structure...

 

[CFSEng]

I would guess room was changed to area to be more general in nature.

Regardless, I agree with Mike, If the building has the possibility of having 300 people in it then I would use 1.15

 

[dengebre]

It does matter because the importance factor can significantly impact the glazing design. It can increase the cost of the glazing by hundreds of thousands of dollars, depending upon the size of the project. Sharp developers understand this and are quick challenge.

 

[archeng59]

If the building has an auditorium, meeting room or classroom where more 300 or more people gather, the entire building is an assembly as far as I'm concerned. I don't design part of the building for an assembly category and the other part as something else. The building is designed for the category having the largest importance factor and greatest load conditions.

 

[dengebre]

ARCHENG59: Agreed. The situation becomes less obvious for an office building. Example: an office building with an occupany of 310 persons per floor and 2170 person total for the building, has no audotoriums or other such assembly spaces. Is the "area" an entire floor (greater than 300 persons) or the largest room on that floor (less than 300 persons)? It may seem like splitting hairs but a 1.15 Importance Factor significantly increases the cost of the glazing, especially in hurricane wind zones.

 

[miecz]

The November 2006 issue of Structural Engineer Magazine has an article that clears this up. It tells how the 2006 International Building Code was reworded on this issue. Apparently, Occupancy Category III was only meant to apply to buildings whose primary occupancy is public assembly. You can find the article at gostructural.com. Browse Issues to November 2006.

 

[MiketheEngineer]

Glazing -- never done that and therefore never thought of it.

These forums are truly great - I learn something every day!!

 

[dengebre]

Conclusion (for future thread searchers): "covered structures whose primary occupancy is public assembly with an occupant load greater than 300" are considered Occupancy Category III buildings and therefore have an Importance Factor of 1.15. Office buildings, that do not include such assembly occupancy spaces, would not be included in this category.*

Thanks to all for the quick responses. Great forum.

*see ASCE 7 Table 1-1 for other criteria not discussed here.

 

[miecz]

dengebre-

Been thinking about your reply about sharp developers being ready to challenge. It will be a sad day when engineering decisions are made by investors. While it's good to understand ASCE7 requirements, they are minimum design requirements, and can always be overridden by the design professional with no reason beyond "gut feel".

 

[DonPhillips]

"It will be a sad day when engineering decisions are made by investors."

This happens all the time. The better you educate your client, the better decisions the investors will make.

Don Phillips

http://worthingtonengineering.com