Reinforcing for architectural concrete sign

[vmirat]

We're designing a sign for a client that is 8' wide x 6' high above grade x 8" thick solid concrete, cast-in-place. This hunk of concrete will have metal lettering and symbols attached to it. It will sit on a footer at 36" below grade (so the total height of the sign will be 9 feet from footer to top). The only live loads will be wind (90 mph).

Is there any reason to reinforce this thing, other than extending rebar up from the footer to tie it together? The concrete by itself is strong enough to resist the wind load.

 

[youngstructural]

Traffic impact, seismic...

If you can truly handle the loads with the concrete well inside the elastic range, I suppose there isn't a reason to reinforce... But I don't think I would ever do it. I really don't think that's what the mass concrete provisions of the concrete codes is intended for.

I've designed a few such signs, and at least one of them was later hit by a car. I would hate to think what might have happened had I not reinforced it.

Also, is it cast in place? What about lifting stresses?

Cheers,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[dougantholz]

I would put some crack control reinforcement - say #3's at 12 EW. There isn't really any load on the thing of consequence. You do not need it to survive a car impact so that isn't a real load. You only want to do one layer becuase you don't want rust staining, but you still need to control some of the cracks.

 

[youngstructural]

I doubt cracking will be of concern with the shape and thickness you're talking about... I stand ready to be corrected, however if your section is not restrained, you should have a very good shape for uniform shrinkage and I would doubt you would even get near 150 microstrains, however I would do the specific calcs if I were you...

And depending on where you are, which code you're applying, and whether the sign is within 5m of a roadway, car impact IS a real load.

The automatic assumption that a poster is in the US is not appropriate, nor is any code all-inclusive of an engineer's duty of care...

Regards,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...