Buckling of beam in different direction

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SUMMARY

The discussion centers on the mechanics of beam buckling, specifically regarding the y-y axis and the use of moment of inertia (Iy). Participants clarify that for y-y axis buckling, the beam rotates about the y-y axis, which is the weaker axis for I-beams. The confusion arises from the interpretation of how the beam bends and the role of cables in preventing movement along the x-axis. It is established that the cables restrain the beam's movement in the x-direction while allowing rotation in the x-z plane.

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  • Understanding of beam mechanics and buckling behavior
  • Familiarity with moment of inertia concepts, specifically Iy and Ix
  • Knowledge of structural support systems, including fixed and pinned supports
  • Ability to interpret structural diagrams and their implications on beam behavior
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  • Explore the effects of boundary conditions on beam stability
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chetzread
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Homework Statement


For the y-y axis buckling , the beam will bend towards either positive or negative y-axis , right ?
I don't understand that why for y-y axis buckling , moment of inertia (Iy) about y-axis is used ?

Homework Equations

The Attempt at a Solution


IMO , it's wrong ... When the beam bend in y direction , Ix is used , rather than Iy [/B]
 

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chetzread said:

Homework Statement


For the y-y axis buckling , the beam will bend towards either positive or negative y-axis , right ?
No. It means the beam rotates about the y-y axis, which is the weaker axis for this I-beam.

I don't understand that why for y-y axis buckling , moment of inertia (Iy) about y-axis is used ?
See above.

The Attempt at a Solution


IMO , it's wrong ... When the beam bend in y direction , Ix is used , rather than Iy [/B]
For someone who has a lot of questions about the bending of beams, you also seem to have a lot of opinions about what is correct and what is not.

It would pay you great dividends to study your texts more carefully on this subject. I know the text you are using leaves a lot to be desired, but the web provides many other resources (and texts) which you can use to help answer your questions.
 
SteamKing said:
No. It means the beam rotates about the y-y axis, which is the weaker axis for this I-beam.
How can the beam rotate ? It can only buckle either in x or y direction, right ? Or do you mean for y-y aixs buckling , it means the beam bend towards positive or negative x -direction?
 
Last edited:
chetzread said:
How can the beam rotate ? It can only buckle either in x or y direction, right ? Or do you mean for y-y aixs buckling , it means the beam bend towards positive or negative x -direction?

When a vertically oriented beam buckles, part of it suddenly starts to deform in rotation. Check the diagram in the extreme lower left corner of the attachment in the OP. The top end of the beam is restrained from moving from side to side, and the y-y axis is pointing perpendicular into the paper in this view. The rest of the beam between the upper and lower ends has nothing restraining it from rotating by various angles as you go along the length of the beam from bottom to top.
 
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SteamKing said:
When a vertically oriented beam buckles, part of it suddenly starts to deform in rotation. Check the diagram in the extreme lower left corner of the attachment in the OP. The top end of the beam is restrained from moving from side to side, and the y-y axis is pointing perpendicular into the paper in this view. The rest of the beam between the upper and lower ends has nothing restraining it from rotating by various angles as you go along the length of the beam from bottom to top.
i'm confused now ... The cable will prevent the beam from moving in y-y direction , right ? why the author stated the cable will prevent the beam from moving along x-axis ?
 
chetzread said:
i'm confused now ... The cable will prevent the beam from moving in y-y direction , right ?
No. How can it?

why the author stated the cable will prevent the beam from moving along x-axis ?
Well, take another look at the diagram. There are two cables attached to the end of the beam, one on either side. If the beam wants to move one way along the x-axis, one of the cables will be put in tension, and the opposite one will probably go slack. Same thing happens when the beam wants to move in the opposite direction along the x-axis.
 
chetzread said:
i'm confused now ... The cable will prevent the beam from moving in y-y direction , right ? why the author stated the cable will prevent the beam from moving along x-axis ?
@SteamKing it's stated in the second lines of notes , the cable will prevent the cables from moving along x-axis ... why is it so ? is the notes wrong ?
 
is it because of the author stated the cable will prevent the column from moving along x-axis , so the cable will allow the column to move in + / - y direction , thus , the pin is said to support the column in y-axis ?
 
chetzread said:
@SteamKing it's stated in the second lines of notes , the cable will prevent the cables from moving along x-axis ... why is it so ? is the notes wrong ?

As I explained in a previous post:
SteamKing said:
Well, take another look at the diagram. There are two cables attached to the end of the beam, one on either side. If the beam wants to move one way along the x-axis, one of the cables will be put in tension, and the opposite one will probably go slack. Same thing happens when the beam wants to move in the opposite direction along the x-axis.

If you are not going to read what others post to your thread, then this process gets very tedious and unproductive.

chetzread said:
is it because of the author stated the cable will prevent the column from moving along x-axis , so the cable will allow the column to move in + / - y direction , thus , the pin is said to support the column in y-axis ?

What pin? As far as I can tell, there is no pin in this structure.

The base of the column is fixed. The two cables are attached to the free end of the beam along the x-axis. As far as I can tell, there are no forces being exerted on this beam in the ±y direction, so the column will not deflect from side to side along the y-axis. However, the column can deflect by rotation in the x-z plane, which is what is shown in the diagrams in the lower left corner and the upper right corners of the attachment.
 
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  • #10
SteamKing said:
What pin? As far as I can tell, there is no pin in this structure.
please refer to the left bottom part of the notes , it's stated that in y-axis the column will behave as the fixed and pinned at the top end .
 
  • #11
chetzread said:
please refer to the left bottom part of the notes , it's stated that in y-axis the column will behave as the fixed and pinned at the top end .
Yeah, but there's still no actual pin here. The column behaves in a similar fashion to one which is fixed at one end and pinned at the other. In this column, the two cables at the top of the column act to partially restrain the movement of the column.
 
  • #12
SteamKing said:
Yeah, but there's still no actual pin here. The column behaves in a similar fashion to one which is fixed at one end and pinned at the other. In this column, the two cables at the top of the column act to partially restrain the movement of the column.
so , the 'pin' will allow the column to bend about x-axis freely (act as cantilever)?
 
  • #13
SteamKing said:
However, the column can deflect by rotation in the x-z plane,
What do you mean by it ? I don't really understand ... In y-y axis buckling , the column bend towards + / - x-axis and vice versa , right ?
 
  • #14
chetzread said:
What do you mean by it ? I don't really understand ... In y-y axis buckling , the column bend towards + / - x-axis and vice versa , right ?
Yes, but it doesn't move from side to side, thus staying in the x-z plane. In case you are wondering, the z-axis runs along the un-buckled length of the column.
 
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  • #15
[quote uid=597855 name="chetzread" post=5552688]i'm confused now ... The cable will prevent the beam from moving in y-y direction , right ? [/QUOTE]<br />No. How can it?<br /><br />
why the author stated the cable will prevent the beam from moving along x-axis ?
<br />Well, take another look at the diagram. There are two cables attached to the end of the beam, one on either side. If the beam wants to move one way along the x-axis, one of the cables will be put in tension, and the opposite one will probably go slack. Same thing happens when the beam wants to move in the opposite direction along the x-axis.
Well, do you mean the column will not move along x axis, but will buckle about y-axis ( column bend towards +/- x axis) ?
 
  • #16
do you have any idea ?
 

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