Open Area in Enclosure Classification

[tmgczb]

When we determine enclosure classification of building，shall area of openings include that of doors and windows？
In some cases, windows are open in windy days. And, in some extreme climate, when windows are damaged by big wind, windows will become real openings. I am not sure if what I am considering is correct or not.

 

[DaveAtkins]

Ah, yes, I think we have all considered this at one time or another. A colleague of mine once joked that we should instruct the building owner to close all windows when a storm is approaching

But seriously, pre-engineered metal building manufacturers do NOT consider doors and windows to be openings when they design their buildings. And that is the approach I have adopted.

I am interested in what others have to say!

DaveAtkins

 

[SandwichEngine]

My take is that normal doors and windows do not count as openings. The code asks for permanent openings, not openings of any kind.

When a storm comes, you're supposed to close your car windows. If you don't and something gets ruined, you don't get to go back to the car designer. Same with a building. You're supposed to close your doors and windows when a storm comes.

The only exceptions I've run across are for large hangar doors on airplane hangars and indoor practice facilities. I've seen some of those buildings called out to consider the worst case impact of either enclosed with the hangar door full loading onto the building or partially enclosed without the hangar door loads for when the door is left open. That's a very specific application though. In most cases, the building owner is responsible for closing openings when leaving them open would adversely impact the building.

 

[haynewp]

Here is the commentary from ASCE 7-16. It includes "doors and operable windows" with other things.

Openings are specifically defined in this version of the standard as apertures or holes in the building envelope which allow air to flow through the building envelope, and which are designed as “open” during design winds. Examples include doors, operable windows, air intake exhausts for air conditioning and/or ventilation systems, gaps around doors, deliberate gaps in cladding, and flexible and operable louvers.

The Guide to ASCE 7 Wind Provisions says this:

The phrase designed as “open” during design winds implies that the openings are either open during a wind event like louvers or vents or can be left open.

There used to be something in the Florida Code that if the windows in debris impact regions are not designed for the impact then they have to be considered as openings. I think both ASCE 7 and the FBC now require openings to be protected in debris impact areas except for a couple of exceptions. This may be more about the protection of occupants against flying glass now and not about designing as enclosed. You could have a glazed door that needs impact resistance but then also could be left open according to the ASCE commentary.

The FBC even has a table now for designing garage doors for wind load with the building qualified as enclosed.
1609.6Garage doors and rolling doors. Pressures from Table 1609.6(1) for wind loading actions on garage doors and rolling doors for buildings designed as enclosed shall be permitted.

I always design as if the doors and windows are shut unless it is under the UFC requirements below. It's not the most conservative possibility assuming all shut, but that is also what most engineers that I know also do. I do know of others that design as if the doors are open, especially in garage or warehouse type buildings. I kind of wish ASCE 7 would have spent more effort clearing this up rather than adding the new partially open consideration. But it seems to be still left up to us to decide if they will close doors and windows during a hurricane. At least for non-UFC projects.

For hangars: The DoD has the provisions for hangar doors being open to a certain wind speed. There is also the air leakage provision around the doors that can be included in the large volume reduction factor for the partially enclosed case they also require for hangars. ASCE 7 commentary says to "consider" partially enclosed for hangars, but the UFC makes it a mandatory consideration. The UFC also requires the overhead doors in fire stations to be assumed as openings with the doors having failed.