Weight load for Steel Lid

[Marvinator]

Hi. Im in the middle of designing a chimney cap which I will build myself. I am making the top and bottom out of ready made galvanized steel trash can lids. (Reason: cheap!)

I"m concerned in my design whether or not I will need to support the center of the top to take more weight (from snow and ice) The manufacturer says that the lids are made from 28 - 30 guage steel. If the lid is 21" round and only supported at the edges, what is the weight limit?

[Kelly_Bramble]

Equations and Calculator to determine stress, strain and deflection:

Circular Plate Deflection, Moments and Stress Equation and Calculator

Sheetmetal Gage Size Chart

Area moment of Inertia

Section Area Moment of Inertia Properties Square At Center

[Marvinator]

Ok. Thanks. Did I say that I have no idea what I"m doing in this regard?
I filled in the calculator, but it seem to be saying the load is a -346...not sure I'm doing this right. LOL
But really thanks for the reply.

[GlennD]

I'm guessing that the calculator is only considering a flat piece of metal, not a formed garbage can lid with ribs and creases to strengthen it. A piece that big could probably barely support it's own weight if it was just flat.

And from the sky is falling department: what happens if this collapses and blocks the chimney? Does the house burn down or does everyone die from CO poisoning? Or does the high efficiency furnace detect the pressure build up and shut off?

[JAlberts]

Glenn

Can your post a sketch or general photo of your assembly so we can better understand your planned design.