Inelastic Plate Buckling 1

[mathlete7]

Hello,
I'm looking at my copy of Niu, 2nd Ed., pg 456 which gives the methodology to calculate a plastic reduction factor for plate buckling. There is a factor for plates loaded in compression as well as plates loaded in shear. For the sake of this discussion I'm considering a plate loaded in shear.
I'm assuming that the appropriate way to use the plastic reduction factors would be as follows:
- Check buckling allowable for shear loaded web assuming elastic buckling (plastic buckling factor = 1)
- If the buckling allowable is less than the web yield allowable (determined via von mises stress) then you have the buckling allowable and you're done.
- If the buckling stress is greater than web yield allowable you need to calculate the plastic buckling reduction factor to determine the actual buckling allowable post-yielding.

The underlying assumption is that I'm performing an ultimate analysis so web yielding before the web buckles is permissible.

Does this sound reasonable?

Thanks for your input...

 

[rb1957]

i haven't read niu (i assume you're talking about his stress book, i have his design book) but a web can quite happily buckle in shear (or compression and shear). it sets up diagonal buckles which carry the shear as tension. see diagonal tension field (wagner) beams.

 

[mathlete7]

I should have stated the additional requirement that the webs are to be shear-resistant for the application I'm looking at. No IDT is allowed...

 

[inertia4u]

mathlete7,

Yes you can set the division between elastic to inelastic at the yield point - which is a slight over estimation. This is because what you are interested in the proportional limit of the material, which can range between 70-80% of Fy or aluminum materials (See MMPDS regarding how to calculate proportional limit-I think it is in section 9).

Also, you need to be aware of clad knockdowns at well.

If you go into the NACA Technical Report Server, and download the "Handbook of Structural Stability", TN 3781 it will have all the information you will need.

BTW, you are correct. As soon as you start to deviate from the linear Hookian E, you will need to start to account for plasticity.

Good Luck,

NERT

-----
Nert

 

[RichardHurwitz]

Go to Bruhn on page C5.7 and use figure C5.13.
With edge rotation simple means that the curve can be used for SS, clamped, and mixed edge conditions.
To determine n accurately use equation (4) on page B1.8
and take a stress strain curve of your material and draw two curves on it. 1) 0.85*E(initial) and 2) 0.7*E (initial) as shown in figure B1.12 in order to determine F0.85 and F0.7.
Equation (3) is missing (3/7) in front of the last term.

 

[rb1957]

if you want to restrict your solution to shear resistant webs ... you'll probably need to limit the size of the panel (the a/b dim'ns)