Solve Shear Flow Problem: Find Correct Area

Click For Summary

Discussion Overview

The discussion revolves around a shear flow problem related to calculating the correct area for shear stress distribution in a structural element. Participants explore the application of the shear flow equation and the appropriate area to use in the calculations, with a focus on understanding the implications of their choices.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant initially calculated the area as 80 x 20 = 1600 mm² but found this led to an incorrect answer.
  • Another participant suggested reconsidering the area of the flange, implying it may be less than the initially calculated dimensions.
  • A later reply indicated a successful recalculation with Q = 7.2 x 10^-5 m³ and I = 52.693 x 10^-6 m⁴, yet expressed confusion over why a different area of 40 x 20 was used instead of 80 x 20.
  • One participant described the shear stress distribution as having two triangles with zero stress in the middle, suggesting that the formula used may not be applicable due to the non-thin nature of the section.
  • Another participant questioned the reasoning behind the values of Q and A used in the calculations, prompting further reflection on the assumptions made.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus on the correct area to use for the calculations, with multiple competing views on the appropriate dimensions and the interpretation of the shear stress distribution.

Contextual Notes

There are unresolved assumptions regarding the geometry of the section and the applicability of the shear flow formula to non-thin sections. Participants have not fully clarified the definitions or conditions under which their calculations hold.

Precursor
Messages
219
Reaction score
0
Homework Statement

The correct answer is circled.
[PLAIN]http://img80.imageshack.us/img80/976/94926993.jpg


The attempt at a solution

I used the equation [tex]q = \frac{VQ}{I}[/tex]

But for Q = Ay, what is the area? My area was 80 x 20 = 1600 mm^2. However, this gave me the wrong answer.
 
Last edited by a moderator:
Physics news on Phys.org
Sketch the shear stress distribution and ask yourself whether the area (of the flange) isn't (less than 80)*20. Also, if you write again, give us your values of Q and I, with units.
 
I tried the question again and got it right with a Q value of 7.2*10^-5 m^3 and an I value of 52.693*10^-6 m^4. However, I am still confused as to why we only take an area of 40x20 than 80x20.
 
If you draw the shear stress distribution for the flange, you will see two triangles with zero in the middle, and maximums over the webs. The nail at A takes approximate the left triangle, and the nails at B the other half. The formula is based on thin sections, which this is not, and so you shouldn't believe the results too precisely. If you were to work this from the same first principles as were used to derive the formula VQ/I then I think you would have a better understanding.
 
Precursor: Why do you think (ii) is the correct answer? Why do you think Q = 72 000 mm^3? Or why did you think A = 1600 mm^2 in post 1?
 

Similar threads

  • · Replies 2 ·
Replies
2
Views
1K
  • · Replies 3 ·
Replies
3
Views
2K
Replies
8
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 11 ·
Replies
11
Views
2K
  • · Replies 2 ·
Replies
2
Views
3K
Replies
2
Views
4K
  • · Replies 1 ·
Replies
1
Views
10K
  • · Replies 5 ·
Replies
5
Views
5K
  • · Replies 2 ·
Replies
2
Views
6K