ASCE 7-05 Sec 6.2 Wind Loads :Enclosure classification
ASCE 7-05 Sec 6.2 Wind Loads :Enclosure classification
(OP)
I have some dilemma on ASCE 7-05 Sec 6.2. Definition of Building enclosure classification.
According to ASCE 7-05 Sec 6.2.,
Building OPEN: a building building having each wall atlest 80% open.
Building PARTIALLY ENCLOSED: a building which complies with both
1-total area of opening in the wall receiving positive external pressure exceeds total area of opening in the remaining building envelope by more than 10% ( area of windward opening shall be 10% more than total area of opening in the remaining sides including roof)
2-total area of opening in the wall recieving possitive external pressure exceeds the lesser of 4ft2 or 1% of area of that wall (minimum area of windward opening shall be lesser of 4ft2 or 1% of area of windward wall )
Building ENCLOSED: a builing that does not comply with the requirements of open or partially enclosed building.
Consider a one-story, 10ft tall box-shaped building having 10ftx10ft footprint. no opening in the roof. Assume each side of the building has 70% opening in walls. How would you classify this building? I have a feeling that it should be classified as "PARTIALLY ENCLOSED". But, according to ASCE 7-05 Sec 6.2 it appears to fall in "ENCLOSED" catergory.
I requested a code opinion from ICC staff and I am waiting on their response.What do you folks think?
According to ASCE 7-05 Sec 6.2.,
Building OPEN: a building building having each wall atlest 80% open.
Building PARTIALLY ENCLOSED: a building which complies with both
1-total area of opening in the wall receiving positive external pressure exceeds total area of opening in the remaining building envelope by more than 10% ( area of windward opening shall be 10% more than total area of opening in the remaining sides including roof)
2-total area of opening in the wall recieving possitive external pressure exceeds the lesser of 4ft2 or 1% of area of that wall (minimum area of windward opening shall be lesser of 4ft2 or 1% of area of windward wall )
Building ENCLOSED: a builing that does not comply with the requirements of open or partially enclosed building.
Consider a one-story, 10ft tall box-shaped building having 10ftx10ft footprint. no opening in the roof. Assume each side of the building has 70% opening in walls. How would you classify this building? I have a feeling that it should be classified as "PARTIALLY ENCLOSED". But, according to ASCE 7-05 Sec 6.2 it appears to fall in "ENCLOSED" catergory.
I requested a code opinion from ICC staff and I am waiting on their response.What do you folks think?






RE: ASCE 7-05 Sec 6.2 Wind Loads :Enclosure classification
If the openings are subjected to negative pressure, then the structure is partially enclosed.
The code now considers that the openings subjected to negative pressure "do not count". So the equation in ASCE 7 is almost always satisfied to "partially enclosed".
RE: ASCE 7-05 Sec 6.2 Wind Loads :Enclosure classification
RE: ASCE 7-05 Sec 6.2 Wind Loads :Enclosure classification
Ron and ajh1, thanks for keeping this discussion going.
I don't expect an opening to be subject to whether negative or possitive pressure. In simple terms, For North-to-South wind, windward (north) walls will be subject to positive pressure and leeward (south)walls to negetive pressure.
I was just trying to understand the rationale behind the definition of BUILDING ENCLOSURE. ASCE 7-05 and its Commentary do not elaborate on this.
If anyone cares to classify 'a simple box-shaped building' mentioned in the begining of the thread and discuss their reasoning it's greatly appreciated.
RE: ASCE 7-05 Sec 6.2 Wind Loads :Enclosure classification
RE: ASCE 7-05 Sec 6.2 Wind Loads :Enclosure classification
1. A (pos) = 70%*(10x10) = 70 sf
A (rem) = 3*70%*(10x10) = 210 sf
A (pos) = 70 sf > 10%*A(rem) = 10%*(210) = 21 sf
2. A(1%) = 1%*(10x10) = 1 sf < 4 sf
A (pos) = 70 sf > 1 sf
----> Partially Enclosed
The language of provosion (1) is not well writen, I guess.
RE: ASCE 7-05 Sec 6.2 Wind Loads :Enclosure classification
thanks for your insight. I am glad you have many calls/email correspondence with ASCE about same question. I will wait and see what ICC staff will have to say on this. but, i couldn't find much about the "other" enclosure classificaiton after reading thru the commentary.
kslee1000:
i guess on the 1st part of your calcs,
A(pos)=70 sf < A(rem)=1.1*210 sf =231 sf that will make it non-compliant to Partially enclosed classificaiton. (According to ASCE 7-05 sec 6.2 Ao>1.1Aoi )
so, this building is ENCLOSED!?! eventhough 70% of the entire building(excluding the roof) is open. really strange, right?
RE: ASCE 7-05 Sec 6.2 Wind Loads :Enclosure classification
That's the reason I "guess" the provison wasn't languaged right. If as stated, the intention does not make sense to me. How often we have the case that opening on one wall more that all others combined + 10% over? Jail house, maybe :)
But a guess is a guess, wait to see the clarification.
RE: ASCE 7-05 Sec 6.2 Wind Loads :Enclosure classification
There is a body of thought, and it has been incorporated in some codes, that if an opening has negative pressure and the remainder of the openings have positive pressure but no impact resistance, the area of the negative pressure openings is assumed to be zero....in this consideration, the equation will point to "partially enclosed"
RE: ASCE 7-05 Sec 6.2 Wind Loads :Enclosure classification
Do you know where it is written (which code)? Just curious.
RE: ASCE 7-05 Sec 6.2 Wind Loads :Enclosure classification
RE: ASCE 7-05 Sec 6.2 Wind Loads :Enclosure classification
The originator of this thread may want to look into it. There must be a explanation on why it deviates from other sources, such as ASCE 7-05.
RE: ASCE 7-05 Sec 6.2 Wind Loads :Enclosure classification
To my knowledge, the IBC (2006) does not contain the same consideration. It is relatively silent on opening protection for windborne debris.
The consideration makes some sense in that windborne debris would only affect the opening when something blows into it (as in positive pressure); whereas debris would be blowing away from the opening for negative pressure considerations.
RE: ASCE 7-05 Sec 6.2 Wind Loads :Enclosure classification
If you have 70% openings on all sides (non-compliance with partially enclosed), that just means the CGpi coefficient is +/-0.18 to be used when determing wall pressures. So exterior and 'interior' walls with exterior exposure would still be designed for wind using the +/-0.18 GCpi.
I would imagine there could be some exceptions for this possibly based on geometry, but that is where engineering judgement comes into play.
RE: ASCE 7-05 Sec 6.2 Wind Loads :Enclosure classification
Consider an aircraft hanger with the big doors open.
regards,
chichuck
RE: ASCE 7-05 Sec 6.2 Wind Loads :Enclosure classification
As I have described earlier, I found the definition of "partially enclosed and enclosed" to be ambigious and incomplete.
RE: ASCE 7-05 Sec 6.2 Wind Loads :Enclosure classification