gas station canopy

huangyhg

gas station canopy
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.  
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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
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.
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
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.
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 re  
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.
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
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.

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.
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.