One Side Open Building

[aggman]

I have a question that I feel ASCE-7 and IBC are vague about but is fairly common. I have a metal framed building with light gage metal sheeting, girts and purlins. The building is completely enclosed on three sides (no openings) and open completely on one side. 25' short x 58' long, x 65' tall with a monoslope roof. The open side is on one of the long walls and the roof slopes 3:12 along the short direction. (High roof 65', low roof 58.75')
By definition in ASCE 7-02 section 6.2 the building is classified as enclosed because each of the walls that see positive pressure are fully enclosed. What the code seems to be vague on is how to apply the wind pressures. The logical approach would be to assume that the wall opposite of the open wall sees both the positive and the negative (suction) wind pressures at the same time. That would mean that you apply Cp = (0.8 + 0.5) = 1.3 to the wall and then adding the GCpi = 0.18 to the wall also. This would be about the same as a free-standing wall defined in figure 6-20 using Cf = 1.2, except the internal pressure is added. I am wondering if this is the approach that others use or am I missing something.

Thanks for your input.

 

[miecz]

I think the intent of ASCE 7 is for this building to be designed as partially enclosed.

 

[aggman]

Well that is what another engineer thought also but if you go through the definition of enclosed, partially enclosed then it is enclosed. (Because the open wall does not see positive pressure.) The other engineers approach was to design it as partially enclosed and use the leeward wind pressure with the GCpi = 0.55 on the interior wall. I don't necessarly disagree with the approach, but to me ASCE 7 is very detailed about what is enclosed and partially enclosed and it would seem to me that it is enclosed. Thanks for your input.

 

[zcp]

aggman,

Reread your definition for partially enclosed.

Condition 1: The open side is a wall that would receive positive external pressure (you have to think as if it was solid with an opening in it.....the "opening" just happens to be the size of the wall). YES

Condition 2: The opening exceeds 4 sq. ft. and no other openings. YES.

You got a YES-YES, so it is partially enclosed.

ZCP

http://www.phoenix-engineer.com

 

[aggman]

I see what you are saying and that procedure makes sense. I guess I am just unsure how a wall that is not there at all is still considered a wall. I guess it has to do with the envelope of the structure.

 

[mrMikee]

This is an unusul problem in that it makes you think about what the windward, leeward, and internal pressures would be in a situation like this. In short, I would design the wall for both the windward and leeward pressures as if it was single stand alone wall. The significance of a partially enclosed building design is that the internal pressures will result in additional loads on walls. But in this case there is no leeward wall.

Regards,
-Mike