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Wind Loads on Open Structures

Wind Loads on Open Structures

Wind Loads on Open Structures

(OP)
If my structure does not meet the design criteria for an open structure or that of a partially enclosed structure am I therefore by definition an enclosed structure?  I am designing a simple gable canopy with a 14" eave. The sides of the canopy are open with the exception of the top 3 feet which are cladded.  By definition less than 80% of the wall area is open (78.5%) so by a strict reading of the code I must consider this structure to be enclosed.  ASCE7-05 defines an enclosed structure as one that does not comply with the definition of open or partially enclosed is to be considered enclosed.  It seems pretty open to me!

RE: Wind Loads on Open Structures

I would still consider your structure to be open.  The cladding could be considered a supplement to the roof...similar to a parapet, but reversed and not truly a wall section.

RE: Wind Loads on Open Structures

Engineering Judgement should be used here.  It is obviously not an 'enclosed' building.

I would run wind loads using 'Free Roofs/Canopies' and check versus 'enclosed'.  From there, you can decide what makes most sense.

Remember, Code Provisions are 'recommended minimums'

RE: Wind Loads on Open Structures

I agree.  Open.

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

RE: Wind Loads on Open Structures

I have always treated similar structures as OPEN (canopies over toll plazas, porte cocheres, gas station canopies). I believe this is how the wind will react on the roof. You also have lateral load on your gable, which I am not sure if ASCE specifically details this situation now. I believe in the past because this situation was not covered, I conservatively took the worse case of a parapet, sign, or enclosed building wall pressure...  

RE: Wind Loads on Open Structures

If you look at the very bottom of section 6.5.13.2 (Open Buildings)in ASCE 7-05, it states that fascia's on roofs with a slope of 5 degrees of less shall be considered as inverted parapets. I am guessing your roof slope is greater than this.

If I understand this standard, if the building is considered "open" by definition, then there are no loads applied to vertical sides, loads are only applied to the roof. These load cases are shown in figs 6-18 & 6-19

I am hoping this post generates more responses as I am not fully comfortable with this standard as it applies to these types of structures that seem to be open type structures.

It seems to me that if the building is classified as "enclosed" then the loads from fig 6-10 (if the structure is low rise) have to be applied over the full wall area regardless of whether it is 79% open or 0% open.

RE: Wind Loads on Open Structures

(OP)
"SplitRings" post is getting to the heart of the matter.  Thanks. I think the real problem lies in the fact that the code does not address these issues using a complete logic path.  It has based this section on limited physical modeling studies and not filled in the blanks for us until such time additional studies can be made to correct the data.  While taking the conservative approach is a pratical answer the code has left pratical behind long ago.  These types of code omisions leave the practicing engineer in a poor postion with regards to his client and some slick laywer out there.  It is good to think of the code as a guide to be used by responsible engineers but the law looks at the code as binding legal requirement and gray areas as profit centers.  The engineers that write the code need to remember this.

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