Calculating Shear Flow in a Hollow Beam: Understanding Mistakes in Dimensioning

In summary, the author tried another method and got 30000 instead of 29750. They are unsure why the ans is different.
  • #1
fonseh
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2

Homework Statement


for shear flow at D , the Q = Ay , i tried another method , i gt 30000 , instead of 29750, why the ans is different from 29750? why can't i use this method( i break the shaded area into 3 parts ( as shown in figure)

Homework Equations

The Attempt at a Solution


Q = Ay = (60x10x35) + (2x30x10x150 = 30000[/B]
http://imgur.com/a/VXDK6
 

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  • #2
The author is wrong the Q is 30 in^3 I don't know why you added those zeroes to get 30000
 
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  • #3
PhanthomJay said:
The author is wrong the Q is 30 in^3 I don't know why you added those zeroes to get 30000
http://imgur.com/a/VXDK6
here' my working , Q = Ay = (60x10x35) + (2x30x10x150) = 30000 , or the author's working 29750 is correct ? which cut is correct ? My cut of section into 3 parts is different from the author's working
, sorry , i posted the wrong notes...here it is
 

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  • #4
Ok then you are correct, good work..
 
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  • #5
PhanthomJay said:
Ok then you are correct, good work..
do you mean the author can't cut the beam like this ? why ?
 

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  • #6
The author cut the beam at the neutral axis to determine Q about the neutral axis, just like you did. But the author messed it up and didn't calculate the areas correctly, what more can I say you are right and they are wrong. Let it be!
 
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  • #7
PhanthomJay said:
The author cut the beam at the neutral axis to determine Q about the neutral axis, just like you did. But the author messed it up and didn't calculate the areas correctly, what more can I say you are right and they are wrong. Let it be!
no , i am concern about how should the beam be cut ? i divided the beam into 3 parts like this(red) , whereas the author divided the beam into 3 parts like this (green), i gt 30000 , but the author gt 29750 , there's a difference of 250 , which is correct ?
i checked thru the author's my working using calculator , i gt 29750 based on his working
 

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  • #8
come on now I keep telling you the author made a mistake !

He/she did not use those green areas...they dimensioned incorrectly. The numbers come out to 27500, but the numbers inputted are wrong. The correct ans is 30,000 mm^3.
 
  • #9
PhanthomJay said:
come on now I keep telling you the author made a mistake !

He/she did not use those green areas...they dimensioned incorrectly. The numbers come out to 27500, but the numbers inputted are wrong. The correct ans is 30,000 mm^3.
sorry , i messed up QC and QD , question solved
 

FAQ: Calculating Shear Flow in a Hollow Beam: Understanding Mistakes in Dimensioning

1. What is shear flow in a hollow beam?

Shear flow in a hollow beam refers to the distribution of shear stress along the cross-section of the beam. It is caused by shear forces acting on the beam, and can be calculated by dividing the shear force by the area of the beam section.

2. How does shear flow affect the strength of a hollow beam?

Shear flow can significantly affect the strength of a hollow beam, as it can lead to shear buckling and failure. It is important to consider shear flow in the design and analysis of hollow beams to ensure their structural stability.

3. What factors influence shear flow in a hollow beam?

The magnitude and direction of the shear force, the geometry and dimensions of the beam section, and the material properties of the beam all influence shear flow in a hollow beam. The type of loading and boundary conditions can also affect shear flow.

4. How is shear flow calculated in a hollow beam?

Shear flow can be calculated using the shear flow equation, which takes into account the shear force, beam section area, and the distance from the neutral axis to the point of interest. It is also important to consider the shear flow distribution along the entire length of the beam.

5. Can shear flow be controlled in a hollow beam?

Yes, shear flow can be controlled by adjusting the geometry and dimensions of the beam section, as well as the material properties. Other methods like using stiffeners and cross-section reinforcements can also help to reduce shear flow in a hollow beam.

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