Maximum shear stress in square tubing

[bigislander72]

Does anyone have the equation for this. I tried one from my textbook, and the answer I get is less than the average shear stress which is impossible. So I was curious to look at onother version, because perhaps the eq. has a typo? Also, does it occur at the neutral axis like it would in a round shaft? I thought I remebered my prof. say not, but I am out of school now; don't have those resources anymore!

 

[nvn]

bigislander72: Yes, the maximum shear stress occurs at the square tube neutral axis, and is tau_max = 0.75(V/t)[b^3 - (b - 2*t)^3]/[b^4 - (b - 2*t)^4], where V = transverse shear force on cross section, b = square tube outside width, and t = wall thickness. This formula assumes sharp corners, or ignores rounded corners, which is a close enough approximation.