gas station canopy 2

[deereman]

An architect is wanting me to design a drive thru that has only 2 posts, similar to the structures they install over gas pumps. Has anyone ever designed one of these? Are the columns designed as a cantilevered column to resist lateral loads? It seem this is a very unstable structure. I've noticed that alot of the new canopies have 4 columns and the ones that have 2 columns have alot bigger columns than the older ones.

 

[BAretired]

Hello deereman,

The columns are designed as cantilevers to resist lateral loads as well as unbalanced snow load on the roof. The foundation must be able to resist these eccentricities. Roof beams must be connected to the top of each column with a moment connection adequate to resist unbalanced wind uplift and snow load.

Structures like this are fun to design. Do not skimp on the column size and enjoy the experience!



Best regards,

BA

 

[ChipB]

Yes, BA is right. These are fun.

It has been my experience (thus far), wind uplift and overturning always controls the size of the foundation.

 

[swearingen]

There's still a bunch of those laying around next to gas stations all over southern Louisiana from Gustav...


If you "heard" it on the internet, it's guilty until proven innocent. - DCS

http://www.eng-tips.com/supportus.cfm

 

[civilperson]

Gas station canopy design specialist crank these cantilever designs out two per day for five hundred dollars each. Soil bearing values vary and make each one unique.

 

[rmw]

This type of canopy doesn't hold up well to being struck by the digging boom of a Ditch Witch trencher either. I can still remember the lurching that was going on complete with all the falling of the florescent light bulbs when I drove that truck with a DW trencher under it and the boom caught the canopy. I hit it a good lick and put quite a tweak in it, but it didn't fall.

I bet that wasn't factored into the original design.

rmw

 

[Ron]

I've done quite a few cantilevered canopy designs...yes, they are more fun than the others. Expect large columns, huge footings, and strong moment connections at the columns as noted by others.

 

[chicopee]

rmw brought out a good point, make sure that the canopy columns are well protected from traffic impacts. For overhead impacts well we can make the whole world "idiot" proof

 

[JLNJ]

Be conservative!

These things (along with pre-engineered buildings) are the first structures you see on the Weather Channel floating away during a windstorm. It says to me that we don't use the same factors of safety for these as we do for other structures. I don't know that ASCE 7 properly covers them.

 

[asixth]

I hear the word 'canopy', 'free roof' and 'awning' thrown around interchangeably (is that a word?). Can someone please inform me if there is a difference between these three forms of roof.

Otherwise, design as a cantilever and ensure that the foundation has capcity to resist overturning. You may be able to use outriggers to tie the columns together in the out-of-plane direction.

 

[hokie66]

asixth,

The use of these words varies somewhat with geographic location, but an awning is usually attached to a larger structure. In the OP, I think canopy is appropriate.

 

[KootK]

I did a repair on one of these in WI. A truck & camper with some crap tied to the top ran into the roof deck. It developed some P-delta action and was enough to tip the free standing canopy into the adjacent wood frame main building. That, in turn, seemed to be enough to cause problems with the door and window operation of the main building. Weird stuff. Part of the problem was probably that 80 of the building walls were glass.

 

[FDiego]

I'd like to contact Ron privately if possible to ask a few things about this thread. Would it be possible Ron?

 

[Bagman2524]

I have a patio canopy near a building, that is similar to a gas station type canopy, that I need to analyze for wind uplift. I don't have a copy of ASCE-7 handy. Can anyone tell me if ASCE-7 addresses calculating uplift forces?
Thanks in advance.

 

[Ron]

FDiego...sorry I didn't see your post until now. Yes, you may contact me through the Eng-Tips procedure.

 

[Lion06]

I was driving a few weeks ago during some relatively high winds (maybe 30-40 mph) and saw a gas station canopy with only columns where the roof of the canopy was moving A LOT. I mean on the order of at least 1.5' at the ends - this did look exaggerated as one end was 1.5' up and the other end was 1.5' down (it reminded me of someone shaking out a blanket with the way the "waves" were moving through the roof). I actually called the station and suggested he have someone look at it since it really didn't look safe. The guy seemed kind of pissed off and annoyed that I called and said that it's supposed to do that. Bear in mind, I didn't talk all high and mighty to the guy (I didn't even say I was a structural engineer). I just called as a concerned citizen.
Is that true? Are they designed to do that? I almost couldn't believe it. If it was moving that much in a 30 or 40 mph wind, what would it do in the 90 mph wind that it was designed for?

 

[JLNJ]

When you have a lot of motion you get a whole additional set of aerodynamic "wing" effects that I don't think ASCE really captures. It seems to me that 18" sway with "fluttering" could spell trouble at higher speeds.

 

[Ron]

StructuralEIT....no it should not do that. That indicates the designer did not limit the deflection of the cantilevered column to a tolerable value.

 

[hokie66]

Sounds like the gas station operator may have done his own design.

 

[haynewp]

"The guy seemed kind of pissed off and annoyed that I called and said that it's supposed to do that."

That's classic.