Open building definition
Open building definition
(OP)
I am designing a freestanding canopy for a gas station in a hurricane region. It has 10 interior columns and a 50'x160' roof. It does not have walls. When looking at wind load, I'm wondering if this is an "open building" (ASCE 7 6.5.13) or "other structures" (ASCE 7 6.5.15). There is no requirement for uplift in "other structures".
If I must design as an "open building", will I need to design the columns for the downward acting pressure shown in figure 6-18A (ASCE 7)in the combination D+0.75Lr+0.75W?
If I must design as an "open building", will I need to design the columns for the downward acting pressure shown in figure 6-18A (ASCE 7)in the combination D+0.75Lr+0.75W?






RE: Open building definition
RE: Open building definition
Seriously, as Hokie says, there is uplift as with any canopy structure.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Open building definition
RE: Open building definition
I have done many canopies, but per NBCC 2005, which does not address wind load for canopy-type structures. I have used an internal pressure coefficient of +1/-1 (I have heard of others multiplying the external pressure by 2, should almost give the same magnitude of pressure.) I determine the wind load on the fascia as a "sign structure." Of course, this is per NBCC 2005, which does not really help you.
I'd exercise extreme caution if you have a single line of columns as opposed to columns that are doubled up along the length of the canopy. Also, most canopy failures occur at the base plates.
I've attached a journal on canopy failures.
Clansman
If a builder has built a house for a man and has not made his work sound, and the house which he has built has fallen down and so caused the death of the householder, that builder shall be put to death." Code of Hammurabi, c.2040 B.C.
RE: Open building definition
Is it customary to provide a deck only on the underside of framing members as shown in the pictures in your link? I don't think that is a good idea at all.
BA
RE: Open building definition
Because of the depth of the "skirting" that hides the roof structure, it also picks up a significant lateral load, so the columns usually have a high moment at the footing.
BAretired...yes, it is customary on gas station canopies to leave the top open, have a reflective underside on the flimsy decking, and hide the structure from bottom and side view.
RE: Open building definition
Done a few of these in the past. Bad design in high snow load areas though.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Open building definition
BA
RE: Open building definition
Any reasons for providing deck only on the underside??
Thanks.
RE: Open building definition
The reason is to save money. It is a bad idea in my opinion. It could get filled up with leaves, bird poop and all kinds of other things, not to mention snow in the winter. It is simply an unacceptable solution. The top should be enclosed with deck.
BA
RE: Open building definition
RE: Open building definition
The wind loads normal to the roof of an open structure include upward and downward forces. When looking at D+.75Lr+.75W for beam and column design, do you include the downward force of the wind with the dead and roof live loads? This can significantly affect the sizes of the members.
RE: Open building definition
BA
RE: Open building definition
When the weather channel shows failures the first thing to go seems to be the gas station capopies. The second are the pre-engineered buildings.
RE: Open building definition
Clansman
If a builder has built a house for a man and has not made his work sound, and the house which he has built has fallen down and so caused the death of the householder, that builder shall be put to death." Code of Hammurabi, c.2040 B.C.