# Shear stress in thin wall beams

1. Dec 10, 2014

### princejan7

1. The problem statement, all variables and given/known data
http://postimg.org/image/9va37id55/
The question is to find the shear stress at the points A, B and C. The solution uses the sectioning planes aa, bb and cc to do so.

For example, at C, how should I know whether to use a horizontal or vertical sectioning plane. Also, how should I know which portion of the beam i would have to consider as A', the bit to the left or right of the sectioning plane ?

2. Relevant equations

Shear Stress(Flange) = q(Flange)/thickness(Flange)
where q(flange) = VQ(Flange)/I

Shear Stress(Web) = q(Web)/thickness(Web)
where q(Web) = VQ(Web)/I

V is the transverse shear force
Q = A'y" is the first area moments of the area A' with respect to the neutral axis

3. The attempt at a solution

2. Dec 10, 2014

### SteamKing

Staff Emeritus
Generally, you have the highest shear stresses acting on the thinnest material.

For example, the shear stress τ = VQ / (I t), so for a given shear force V, the smaller t is, the higher the stress τ.

The shear stress will be zero at any free ends of the section. Start from the nearest free end and work toward the section plane at which you wish to calculate the shear stress.