Wind Load on Sign Letters At Roof Edge

[Boiler106]

Letters are roughly 8 ft tall and at the edge of a 70 ft tall building, in plane with the wall, using IBC 2015 and ASCE 7-10.

Letters are also about 12" wide and rectangular. I have the surface area of each individual letter.

My thoughts are to use parapet wind loading as it does not seem to fit 'solid attached signs'.

Can anyone tell me im wrong with reasoning and point to a reference? Im certainly willing to entertain references to ASCE 7-16

 

[phamENG]

Are these letters sitting on top of the wall, or up against the wall just below the top? I'm guessing the former based on your desire to use parapet loading. If so, it seems reasonable to me.

 

[Boiler106]

they are sitting in plane with the wall but above the free edge of the wall, similar to a parapet.

(edited typo from 'plan' to 'plane')

 

[phamENG]

You might run both calculations and see how the resulting loads compare. But the parapet loading does seem appropriate to me.

 

[dhengr]

Boiler106:
But then, you must have some minimal angle iron A-frame, truss framing system for the 8’ high letters to sit on and to absorb the wind lateral loads from each letter. Parapet loads, corner region cladding loads, some likely vortex shedding all seem to possibly be in play. Be pretty conservative with your letter loads, there is exposure from every possible direction, and with really funny shape factors. Those things bounce and rattle around up there individually and then back to their angle iron frame. Give or take a little lat. load, this shouldn’t change your truss framing too much. The front legs and the rear kickers probably sit in pitch pockets or small column stubs through the roof system. Are the letter bodies about 12” square sheet metal, 3 sided cans, with internal lighting and a plastic face, or some such? You usually can’t just cantilever them off their bottoms. The cans will have a half dozen tabs, studs (for wall mounting), maybe a couple angles full letter height on their back face, or the like, which get attached to your truss frame, which has a front truss frame plane for this attachment.