Formula for shear force 1

[bojoka4052]

When I want the highest amount of shear force tau_max I use 3/2 x V/A as seen below:

However I saw someone use 8/7 x V/A. I was wondering if anyone has seen this equation before where they use 8/7 instead of 3/2, is it a special case?

 

[HTURKAK]

Max. transvese shear stress for rectangular sections τmax =(3/2)*V/A ... For τmax = 8/7 x V/A The section could be probably thick circular , elliptical etc..