Steel cover plate design 1

[WJA]

I have been asked to provide a steel cover plate, which is for decorative purposes only. This is outdoors, exposed to wind. It will be supported by 2 steel angles approx 2 feet apart, so a span of 2 feet. How do I go about determining the thickness of this plate? Do I simply design it to be strong enough to not yield under the wind load, or is there a deflection limit to consider as well? I imagine it could vibrate/oscillate in the wind if it's too flimsy?

Thanks!

 

[SlideRuleEra]

I would consider the plate to a very wide simple beam with a 2' span.
Use a simplified uniformly distributed wind loading of, say, 20 lb/ft² (or whatever).
Assume a reasonable maximum (center) deflection, say 1/4".
Then work the problem "backwards":

1) Values for deflection, loading, span (L), and steel's modulus of elasticity (E) are known. Solve for required moment of inertia (I).

2) Values for I and width of the plate (2') are known. Solve for plate thickness (d).

3) Values for I and d are known. Solve for plate's section modulus (S).

4) Value for S is known and bending moment of the plate (beam) can be calculated. Solve for plate's bending stress.

Based on the results of Step 4, adjust either the assumed deflection, assumed wind pressure, or plate thickness to get a reasonable bending stress.

IMHO, there is no "right" answer, just engineering judgement based on calcs made using reasonable assumptions.

For vibration / oscillation... is it really worth the trouble (cost) of detailed investigation / calculations?

http://www.SlideRuleEra.net

 

[GC_Hopi]

Also wind loading usually has a low frequency (dynamically) and the plate described with be quite stiff given the span and material. This means the plate with have a high natural frequency making any dynamic excitation from the wind very unlikely. I agree with SRE that it is not worth investigating based on engineering judgement. You can always model the plate or use formulas to get natural frequency and compare that to the wind.

 

[TLHS]

Honestly, if it's literally just going to sit there not taking any load but some wind, I'd probably just go with 1/4" plate and call it a day. If you aren't comfortable with that, size it up a bit.

The cost of the plate isn't worth detailed investigations unless this is really long in the other direction. Keep that in mind when determining how much engineering time to spend on this. Don't spend an hour playing with +/- 1/8" of thickness.

 

[BridgeSmith]

We use 1/8" aluminum panels for roadside signs, with backing angles at up to 36" spacing and cantilevers of 15".

If you're only doing one, or a few, of these, you've already spent more time on this than the material cost you could possibly save by analyzing it.