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stiffened cylinder under bending moement

stiffened cylinder under bending moement

stiffened cylinder under bending moement

(OP)
Hi,

I have devlop the  program for the stiffened cylinder under buckling. Now i want to add stresses due to bending moment  in it using the relation stress: SIGMA= My/I.  So that i could add it in the stresses develop in due to axial compression. here I=Icyl+Istrnger+Iring

The question is how to calculate the y in section modulus(I/y). I know the 'Istrn and Iring' for stringer and ring (Channel) at thier centroid, does the y simply the distance between the outside edge of the flange from the centroid?

Do i need to use parallel axis method to transform 'Istrn and Iring' calculated at stiffer centroid to shift it to cylinder axis?

Really need help.

RE: stiffened cylinder under bending moement

In calculations in BS 5500, the pressure vessel code, no parallel axis method is used for stiffener rings. I would refer to that or similar codes to check your method.

corus
http://www.corusresearch.com

RE: stiffened cylinder under bending moement

Let me state what I think you are asking:
You have a circular cylinder with longitudinal stiffeners.
This cylinder is loaded with axial compression and longitudinal bending moment. Like a beam-column.
If that is the case then the "y" is the distance from the cross-section's center of gravity to the point you are interested in finding the stress. In the expression
stress = My/I,  I is for the entire cross-section as stated in the parallel-axis theorem( Ixx = Io +Ad^2).
Assuming this is a symetrical section, then if you want the stress in the shell, then "y" is the shell radius. If you want the stress in the stiffener, then "y" is the distance from the entire section's C.G. to the outer edge of the stiffener.

RE: stiffened cylinder under bending moement

(OP)
Thanks warrenw,

What i understand from your answer, is that for symmetrical case (as that of stiffened cylinder), y=Radius of cylinder for thin cylinder and y=distance from center of cylinder to outer edge of flange for stiffner.  is it true?

Also, i have 'I' for stiffners at their centroid, should i use it or transform it to cylinder longitudinal axis using parallel axis theorm.



RE: stiffened cylinder under bending moement

Your "y" values are correct.
As I said above, "I" should be for the entire cross-section
I(entire section)= I(cyl.)+I(stiff.) +Ad^2(cyl.)+Ad^2(stiff)

RE: stiffened cylinder under bending moement

(OP)
Thanks again,

in equation
I(entire section)= I(cyl.)+I(stiff.) +Ad^2(cyl.)+Ad^2(stiff)

Do i need to use Ad^2(cyl.), since I(cyld)=(PI/64)*(Dou^4-Din^4), give I at its center.

RE: stiffened cylinder under bending moement

In your case the cylinder "d"(the distance from the entire section C.G to the cylinder C.G.) = 0 ,so Ad^2(cyl.)=0

RE: stiffened cylinder under bending moement

Dravid,

I am not sure whether I got you. But to avoid buckling, you provide circumferencial stiffeners which are useless in bending.

For bending, you add longitudinal stiffeners. But these stiffeners don't stop buckling. Correct me if I am wrong.

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