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# Shear Stress on Plate - Mystery Equation2

## Shear Stress on Plate - Mystery Equation

(OP)

I am reviewing an already approved (not by me) hand calculated stress analysis of applied loads on an aluminum plate which has structural ribs on its underside. The plate was cut in half, exposing the structural ribs and the Max Moment, Max Torque and Max bending stress was found. The engineer then calculates the shear stress using the Max Torque found. The equation used looks familiar, but I am unable to find its origin anywhere in Roark's Stresses and Strains book.

It's the equation for Fs (see image) This looks so familiar, but I cannot find the original equation. Any ideas where I can find info in this equation? Thank you

### RE: Shear Stress on Plate - Mystery Equation

Hi DustyK

Well it appears to be the J value for the torsional stiffness of the flat plate and the vertical ribs however I cannot find an identical example, if it were me I would politely ask the designer who did the original calculation to show me the reference he used.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

### RE: Shear Stress on Plate - Mystery Equation

I'd take a look in Bruhn, I think there's a similar/identical torsional shear stress equation there. Though it does look pretty standard anyway...

### RE: Shear Stress on Plate - Mystery Equation

(OP)
Thanks for responding @DesertFox. Unfortunately, I do not have access to the engineer who wrote this. His reference was the Roark book, Case 30,Table X which does NOT exist, lol. BUUUUUUUUTTTTTT you put me on the right track. Here is the website I found, https://engineeringlibrary.org/reference/beam-tors... and I think this is it:

Seriously, thank you so much!

### RE: Shear Stress on Plate - Mystery Equation

Hi DustyK

You’re welcome

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

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