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RE: Enclosure Determination

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See below.

Regards, Harold Sprague


From: RichardC(--nospam--at)
To: seaint(--nospam--at)
Date: Mon, 29 Mar 2010 18:36:48 -0400
Subject: Enclosure Determination

I seem to find a lot of variation from one engineer to another in the answer to this type of question – so wanted to pull from a large audience.


Lets say that you have two enclosed buildings and an architectural roof/cover spanning between to the two.  Two opposite sides are completely open, while the other two opposite sides are closed .

Lets say that the roof system is attached to both structures. 

Is it :

1. Enclosed; because it is attached to enclosed structures (or b/c it doesn’t fully meet either open or partially enclosed)

2. Open; because the only direction that receives direct wind loading will flow thru the structure

3. Partially Enclosed because the side walls don’t meet the classification of Open (or do the side walls not count because they do not receive ‘external’ pressure, as defined for Ao?)

I would opt for open so that the uplift is properly charachterized for the reasons you state. 


Now, consider that the system is self supporting, separated and unconnected by some minor amount from the other two structures – does the answer change?

1. Yes; state what the new category is

2. No

The answer should not change.  The structure does not know the difference.  The only thing worth evaluation is the trib area of the components. 


What if the buildings that the systems attach to are high-rise buildings, while the system is only at a low elevation – which mean roof height should the system’s wind pressure be based on?

1. The tallest building’s height

2. The pressure applied at the height of the system in question.  (seems obvious, but I’ve had goes with others on this one more than once…)

Use the tallest building.  This has been fairly well studied, and I have seen a few wind tunnel studies on this.  Use the taller building to predicate the wind pressure unless you are 30 feet or more from the building.  The stagnation pressures at the lower elevations are the same as the upper.  When wind tunnel studies are conducted the pressure contours make this fairly obvious.  The 30 feet is just based on the studies that I have observed in the past. 


I know these subjects are mostly a matter of engineering judgment, but I’m very curious on how much of a consensus may exist here.


You may email me privately if you wish, but the more responses, the better the end result.  Once I receive enough, I’ll send out how many answers were received for each case.


Thanks you in advance for your input.


Richard Calvert


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