Carport Wind Loads
Carport Wind Loads
(OP)
I am currently designing a carport for a client. The required wind loads are IBC2009 utilizing ASCE7-05. The dimensions of the carport LxWxH = 180'x24'x10'. The carport is open on three of the four sides with the back 180' wall of the carport a solid wall (area is to be used for storage).
A question has come up with regards to wind loads and if the roof pressures should be calculated as if the structure were an overhang. Since the building is partially enclosed and the structure is in a relatively high wind zone (115mph exp C) we are ending up with some pretty high numbers. However, this approach seems pretty conservative.
How would others treat the design of the roof with regards to wind? Would you conservatively consider the roof to be an overhang, or would you approach the problem a different way?
A question has come up with regards to wind loads and if the roof pressures should be calculated as if the structure were an overhang. Since the building is partially enclosed and the structure is in a relatively high wind zone (115mph exp C) we are ending up with some pretty high numbers. However, this approach seems pretty conservative.
How would others treat the design of the roof with regards to wind? Would you conservatively consider the roof to be an overhang, or would you approach the problem a different way?






RE: Carport Wind Loads
To be most conservative, assume wall is breached, so that wind must be considered for open roof in both directions.
"Overhang" does not seem appropriate for open building with relatively large plan dimensions, especially compared to low height.
John F Mann, PE
www.structural101.com
RE: Carport Wind Loads
RE: Carport Wind Loads
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Carport Wind Loads
More recent edition (ASCE 7-10) has similar provisions........though wind design is now provided in several chapters towards back of code.
See 27.4.3 and Figure 27.4.7.
Interestingly, your condition does not satisfy code requirements (ASCE 7-05 & ASCE 7-10) for "Open" building or "Partially Enclosed" building and therefore would have to be considered "Enclosed" building as the default (per code); see Definitions. This is where "engineering judgment" must be used!
John F Mann, PE
www.structural101.com
RE: Carport Wind Loads
Ao=1800 ft2
Ag=1800 ft2
Aoi=320 ft2
Agi= 5720ft2
Ao/Ag=1.0 (however each wall is not 80% open as one is 100% closed)
Ao/Aoi = 5.625>1.1
Aoi/Agi = 0.056<0.2
Hence the building is partially enclosed in this direction. Is this not correct?
RE: Carport Wind Loads
Then, for wind parallel to long wall......Ao is full area of (missing) endwall. Although this may sound silly......consider one endwall consisting only of a very narrow solid strip (vertically, but perhaps horizontally also), such that open area is 98% (or 92% or similar).
I submit these code provisions are not intended for such condition......see definition for "Building Or Other Structure, Regular Shaped".......then refer to conditions for use of code provisions (6.4.1.1 & 6.4.1.2 in ASCE 7-05).
Essentially, your structure as configured is not really a "building" as defined by wind-load provisions.......such that you must use engineering judgment .........as suggested in previous posts.
Agi must include area of the 3 open (missing) walls as well as area of roof.......which results in much greater value.
Similarly.....Aoi must include area of "openings" in each wall (not including wall subject to positive wind pressure) and roof
Since the 80% open condition is not satisfied for long wall, the "building" does not satisfy requirements to be considered Open (even if it were considered to be a "building", which it does not).
Especially for wind direction parallel to long wall..... it looks like provisions as noted in previous posts should be used.
John F Mann, PE
www.structural101.com