ASCE 7-10 - Definition for "Partially Enclosed"

[dbnerds]

I've searched high and low (here and all points of the Google globe) but still not satisfied.

I pose a simple scenario:
A building that is 25'x25'x25'tall.
It has one opening in one wall that is 5 s.f.

According to the definition it IS "partially enclosed".

Ao = 5sf
Ag = 25x25 = 625sf
Aoi = 0sf (no other openings besides the one)
Agi = (the non-opened walls & roof) = 4x 25'x25' = 2500sf

The satisfying conditions:
Ao > 1.1Aoi = TRUE, 5 > 1.1x0
Ao > minimum of{4sf or 0.01Ag=0.01x625=6.25} = TRUE, 5 > 4
Aoi/Agi < 0.2 = TRUE, 0/2500 < 0.2

I can't believe the code implies this scenario would be partially enclosed. This scenario stays true (i.e. defined to be Partially Enclosed) when you enlarge the building but keep one opening just barely over 4 s.f. -- which seems even more ridiculous.

Maybe my math is off and/or I'm interpreting the walls/openings incorrectly.

Would appreciate some help on this.

Thanks,

 

[JedClampett]

Sooner or later the code has to be printed up. So they have to fish or cut bait. So you're absolutely right. It doesn't seem logical to me either, that one opening 2'-3" by 2'-3" would increase the parameters by the proportions that going from enclosed to partially enclosed. But if there's a windstorm and it's pressurizing the building due to that one opening, there will be some affect.
Another way to put it is; would you prefer a sliding scale for partially enclosed effects? That code is complicated enough without adding that.

 

[dbnerds]

I'm a little embarrassed that I just realized there was a Reduction Factor for large volumes (section 26.11.1.1) that helps melt the 0.55 GCpi for partially enclosed. Seeing that a lot of our work is factories, this reduction factor will fit in nicely.

As for sliding scales...
I try to make as many excel sheets to do my work as possible, so long equations only bother me once (when programming) -- after that, I don't mind.

As for my example:
I think the equations should involve a variable based on the VOLUME of the space -- afterall we are talking about the pressurized of a space. The wall areas already in the equations are closely related, but not directly (like a volume variable would provide). I dunno.

I'm less frustrated since I"m able to use the reduction factor, which can bring the 0.55 down to 0.275 (in some cases) -- thats WAY less of a jump from an fully enclosed factor of 0.18.

 

[dbnerds]

While I'm venting.
lets look at the definition of OPEN too and this simple scenario.

- An new structure that is an "open" canopy (ie. no walls) except that it has one face backed up against an existing fully clad building.

Definition of Open Building says "..EACH wall be at least 80% open".
The "wall"/face of the canopy structure that is adjacent to the existing building is NOT 80% open, thus the building is NOT open -- but intuitively you "know" its open.

thoughts?

 

[dcarr82775]

Use your engineering judgement. The code isn't intended to be a cookbook and more often then not I have to make a call on how to apply the God forsaken provisions of the wind code (the worst of all in my opinion). It you think it is open then go with it. I can envision more uplift on to roof because pressure will build on the underside against that wall.

 

[slickdeals]

In that case you will use the wind pressures from an open building with more than 50% blockage. This has been discussed numerous times here. As dcarr says, use your engineering judgement.

 

[Splitrings]

I am glad to hear I am not the only one that has shaken my head at the ASCE 7 Wind Provisions. I guess what is most frustrating is the lack of supporting documentation for each case. I have been designing pole barns which one would think is an open building. As soon as you sheath just the gable end of the truss it becomes a partially enclosed building. I guess you need to use your engineering judgement and go with it.

 

[ebava]

dbnerds,
Where did you find the "Reduction Factor for large volumes (section 26.11.1.1)?" There isn't a Section 26 in the ASCE 7-05 that I could find.

I'm running into a similar argument about partially-enclosed or not with a pre-engineered metal garage.

Thanks

 

[Splitrings]

In ASCE 7-05 the reduction factor is in section 6.5.11.1.1

 

[ebava]

That makes more sense. Thank you very much!

 

[Archie264]

Don't forget to multiply the final result by your grandmother's shoe size and the ratio of sardines vs. herring caught in Norway. Or am I thinking of the ASCE 7-15 edition?