# Shear stress at different points

1. Jul 31, 2016

1. The problem statement, all variables and given/known data
in the formula of shear stress, t is the width of member's cross sectional area calculated about neutral axis.
for τc , why t is 6.4 ? Why not 102.1 ?
second question, why we have to consider that specific area? Cant we consider the (red) area?

2. Relevant equations

3. The attempt at a solution
IMO, t for τc is 102.1

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Last edited: Jul 31, 2016
2. Aug 4, 2016

### shina

I have a PDF on sheer stress. This PDF will answer all your questions. But I don't know how to send it.

3. Aug 4, 2016

### Staff: Mentor

PLEASE make though that the pdf does not contain the answer to the OP's post as we can only help with hints and not actual solutions.

4. Aug 4, 2016

Can you help? btw, here's the file that I received from @shina

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5. Aug 5, 2016

### shina

Yaa as you was interested in that PDF I send it to you. It contains only hints which are related to your question. I am little bit perplexed what you reply. I am not getting what are you trying to say. You are not able to open that PDF or what you really want to ask

6. Aug 5, 2016

i still dont understand , can anybody help ?

7. Aug 5, 2016

t is the thickness of the area above region B , right ? since B and C are on the same x-axis level , so the area in the calculation of τc is same as τB , right ? so t(thickness) = 102.1 ?

8. Aug 5, 2016

ok, now i understand a few things now...
But, the t in τc is confusing...
When τc act at the web , it would be 6.4, when it act at the flange , it will be 102.1, right?
But, the question doesnt tell it act on the web or flange, how to identify it?

9. Aug 11, 2016

bump,
But, the t in τc is confusing...
When τc act at the web , it would be 6.4, when it act at the flange , it will be 102.1, right?
But, the question doesnt tell it act on the web or flange, how to identify it?

10. Aug 23, 2016

### SteamKing

Staff Emeritus
The problem clearly states that the student is to sketch the distribution of shear stress along the cross section of the beam. This implies finding the shear stress in the beam everywhere from the upper flange to the centroid.

The shear stress values are not continuous for an I-beam due to the change in width between the flange and the thickness of the web.

Since $\tau = \frac{VQ}{I⋅t}$

the flange produces a certain value of Q while I is fixed for the cross-section. The shear force V is given. When calculating $\tau$ at the junction of the flange and web, one must first take the width of the flange for t and then the thickness of the web. Since these two values of t are very different, so will be the calculated values of $\tau$.

11. Aug 24, 2016

do you mean at B , the author mean the shear stress at flange ? at C , the author show the shear stress at web ? If so , the diagram is confusing ? at C , it could also represent the shear stress at web , right ?

12. Aug 24, 2016

### SteamKing

Staff Emeritus
Given the location of B, the shear stress there can only be the shear stress in the flange.

At C, since there is a connection between the flange and the web, depending on if you are a little above C or a little below, the shear stress will show the sudden change as indicated in the stress diagram for shear stress in the lowest portion of the flange versus the shear stress at the connection between the flange and the web.