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I am reaching out to see if anyone can provide additional commentary, backstory, supporting information, studies, etc. regarding this statement in the commentary of ASCE 7-16 (the last sentence of Section C26.13), "Because of the great amount of air leakage that often occurs at large hangar doors, designers of hangars should consider using the internal pressure coefficients in Table 26.13-1 for partially enclosed buildings." It is interesting that this statement exists only in the commentary as it has a significant impact on the design of large aircraft hangars. Based on our findings and a review of the literature, we believe that this statement should exist in the body of the code rather than be limited to the commentary. Note that this statement appears as far back as ASCE 7-98 in the commentary.

It is our understanding that air leakage around the hangar door leaves at the design wind event will occur, as mentioned in the commentary, and based on our evaluation of several large hangars and various hangar door manufacturer's details. Leakage around the flexible weather seals of each door leaf on horizontal sliding hangar doors for Group I or Group II size hangars (hangar door heights of 28ft+ and hangar bay areas greater than 20,000sf) will readily exceed the maximum 4sf total opening requirement (or 1% of total wall area) for enclosed structures; thus, triggering a partially enclosed condition. This with the hangar doors fully closed. If, as called for in the commentary, air leakage at the hangar door seals is considered, the opening area calculations will most often result in a hangar with hangar doors fully closed to be correctly classified as partially enclosed.

For example: Using a 28ft door height, 140ft wide door opening, 6 door panels, and assuming a 1" gap around each door leaf = 39.66 sf. ASCE 7 does not offer guidance on the amount of gap to consider, but a 1" gap appears reasonable at the full design wind event when reviewing various hangar door manufacturer's details and taking into consideration building and hangar door movement, i.e., building racking, roof uplift, deflection of door system. A gap as small as 1/4" will trigger the partially enclosed classification. The Department of Defense acknowledges that there will be significant door leakage for large hangars based on the language in UFC 3-301-01 (October 2023). The UFC requires the hangar designer to classify the hangar as partially enclosed and to assume a 2" gap around each door leaf for calculating opening area around the hangar door leaves.

#WindandWindLoads

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Jori Lemmon, SE, M.ASCE

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Thank you for the question and observation. As you note the commentary is too rooted in history to determine why it was placced in commentary, rather than provisions.  Regardless, I have forwraded your observation to the ASCE 7 Wind Committee for consideration of a possible move into the provisions.

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Ronald Hamburger, SE
Consulting Principal
Simpson Gumpertz & Heger
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Original Message:
Sent: 12-11-2023 03:54 PM
From: Jori Lemmon
Subject: Hangar Door Air Leakage

I am reaching out to see if anyone can provide additional commentary, backstory, supporting information, studies, etc. regarding this statement in the commentary of ASCE 7-16 (the last sentence of Section C26.13), "Because of the great amount of air leakage that often occurs at large hangar doors, designers of hangars should consider using the internal pressure coefficients in Table 26.13-1 for partially enclosed buildings." It is interesting that this statement exists only in the commentary as it has a significant impact on the design of large aircraft hangars. Based on our findings and a review of the literature, we believe that this statement should exist in the body of the code rather than be limited to the commentary. Note that this statement appears as far back as ASCE 7-98 in the commentary.

It is our understanding that air leakage around the hangar door leaves at the design wind event will occur, as mentioned in the commentary, and based on our evaluation of several large hangars and various hangar door manufacturer's details. Leakage around the flexible weather seals of each door leaf on horizontal sliding hangar doors for Group I or Group II size hangars (hangar door heights of 28ft+ and hangar bay areas greater than 20,000sf) will readily exceed the maximum 4sf total opening requirement (or 1% of total wall area) for enclosed structures; thus, triggering a partially enclosed condition. This with the hangar doors fully closed. If, as called for in the commentary, air leakage at the hangar door seals is considered, the opening area calculations will most often result in a hangar with hangar doors fully closed to be correctly classified as partially enclosed.

For example: Using a 28ft door height, 140ft wide door opening, 6 door panels, and assuming a 1" gap around each door leaf = 39.66 sf. ASCE 7 does not offer guidance on the amount of gap to consider, but a 1" gap appears reasonable at the full design wind event when reviewing various hangar door manufacturer's details and taking into consideration building and hangar door movement, i.e., building racking, roof uplift, deflection of door system. A gap as small as 1/4" will trigger the partially enclosed classification. The Department of Defense acknowledges that there will be significant door leakage for large hangars based on the language in UFC 3-301-01 (October 2023). The UFC requires the hangar designer to classify the hangar as partially enclosed and to assume a 2" gap around each door leaf for calculating opening area around the hangar door leaves.

#WindandWindLoads

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Jori Lemmon, SE, M.ASCE

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