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Author Topic: local buckling of beam web (shear- compression - bending)  (Read 10308 times)

ohba

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local buckling of beam web (shear- compression - bending)
« on: February 05, 2009, 01:22:48 PM »
For the open beam familly is there a way to include MS calculation for local buckling of the beam web.
It seems that for the moment, in the case of the I beam concept, the lightest configuration that HS will tend to give is very thin web with large flanges (which is indeed effecient in terms of pure bending stress point of view).
But I could not find a way to include the failure mode of  local buckling of the web. This is usually considered by including a plate buckling analysis in shear (shear in plane of the web) and combined sometimes with pure bending buckling.

In my present calculation, there is a MS calculated for local buckling, but I'm not quit sure what it represents (and MS are very high), it is called in the failure MS  : "Flange top (/ bottom)- 2 sided - local buckling, shear direction" ??

Phil

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Re: local buckling of beam web (shear- compression - bending)
« Reply #1 on: February 06, 2009, 10:16:05 AM »
HyperSizer takes your overall beam load and resolves that load into unit forces, Nx and Nxy in the beam web, and in the flanges.  You can see the loads that HyperSizer has resolved for each of these objects on the Object Loads tab.

The beam web should have three local buckling modes available:

1. Longitudinal
2. Shear
3. Interaction

If the load in the web is compressive Nx, then you will get a longitudinal margin.  This margin is calculated by doing a panel buckling analysis of a flat plate representing the web with simple-simple boundary conditions.  If the web load is shear, Nxy, then you should get a shear margin, and if you get both compressive Nx and shear Nxy, then you should get an interaction margin.

If you are getting this margin, "Flange top (/ bottom)- 2 sided - local buckling, shear direction", that means you have a shear load Nxy in the top flange object.  This indicates that the overall beam has a shear load V2, or bending and shear in the 2 direction of the beam.  If that is your loading, then you will not get any buckling or load at all in the web.

Can you tell me what kind of loading you have on your beam and what loading is HyperSizer presenting to you on the object load tab?

ohba

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Re: local buckling of beam web (shear- compression - bending)
« Reply #2 on: February 12, 2009, 02:54:53 PM »
Hello Phil,

I found my error : I was using FE results from a model that had the wrong beam element orientation. I corrected the FE (switched Y-axis and Z-axis). And i now get the proper load (i.e higher load in plane 1 as expected) and then I get the proper failure mode for the web local buckling.

Thanks anyway