How do I find the critical value of shear stress?

[w31ha-]

Homework Statement

Finding the critical value of shear stress at the junction and at the neutral axis

Homework Equations

stress max = (Bending moment x height from neutral axis)/Moment of inertia
Shear stress = Shear force/area

The Attempt at a Solution

I am able to do the first 2 parts but not the last one. I'm not really sure which of the 2 equations to use and what it meant by critical value.

 

[SteamKing]

Homework Statement

Finding the critical value of shear stress at the junction and at the neutral axis

Homework Equations

stress max = (Bending moment x height from neutral axis)/Moment of inertia
Shear stress = Shear force/area

The Attempt at a Solution

I am able to do the first 2 parts but not the last one. I'm not really sure which of the 2 equations to use and what it meant by critical value.

You are not going to be able to calculate any meaningful shear stresses with the formula:

Shear stress = Shear force/area

This formula:

stress max = (Bending moment x height from neutral axis)/Moment of inertia

is not for the maximum stress. It is the general formula for calculating only the bending stress, which may or may not necessarily be the maximum stress.

For this type of section, the shear stress is zero at the outer fibers of the flanges and a maximum at the N.A.

At points where there is a change in the distribution of material, at the junction of the flanges with the web, there is a drastic change in shear stress.

Find a better formula for shear stress and you'll have better success analyzing this problem.

 

[paisiello2]

Do you know the shear flow formula?