web thickness buckling

[CondensedMatter]

I have an application with a steel plate hogout, with webs (stiffeners) machined in. This plate will be subjected to bending such that the webs will experience both tension and compression.

The plate is weight sensitive (less=better), so I'd like a deeper plate with very thin webs, however, I'm concerned that these webs will buckle or wrinkle. Does anyone know any rules of thumb / best practices / formulas I can reference for this application?

thanks in advance

 

[LittleWheels]

What size are you talking about? Various standards for hot-rolled steel beams refer to design of web stiffeners. Cold-rolled steel sections like purlins are similarly thin and subject to buckling, so their standards may be useful. These standards may not be directly applicable though.

 

[GregLocock]

Can you post a picture of your proposed design, and the likely loading?

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[JStephen]

Refer to AISC ASD/ LRFD.

Keep in mind that these are oriented towards buildings, and in some cases allow for inelastic action. For other applications, you may need to reduce stresses or consider fatique or vibration issues more carefully.

 

[GregLocock]

I've never found building codes any help at all for detailed dynamics designs. Odd that.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[CondensedMatter]

This isn't a fatigue problem; we're only talking a few cycles in its lifetime. 99% of the time its dormant.

As far as geometry, I dont have pictures, but think of a one-sided waffle iron. A large steel plate, 2.5" thick, with a square hogout pattern. MAterial will probably be either HY80 or HY100. Driving loads are pressure applied on the top (flat part). Plate will be simply supported around the perimeter.

 

[GBor]

Sounds a lot like a door panel of a standard US Navy door, except that they stamp the door panel (uniform thickness, not hogged). They use FEA to analyze the door...including helicopter hangar doors and stern gates (the big ones in the back that tanks, LCAC's, etc. exit).

Garland E. Borowski, PE
Borowski Engineering & Analytical Services, Inc.
Lower Alabama SolidWorks Users Group

 

[GregLocock]

OK, that's a standard design case in the aircraft industry. So if you want a manual method, check out Bruhn.

The limiting failure mode is likely to be some form of buckling in the web in compression, although there is a lateral instability mode in tension as well.

I don't know of a detailed reference other than Bruhn. I'm sure one exists, but it is not the sort of structure I design. Roughly speaking it is a T section, for the sake of argument, so that's where I'd look.

I also doubt that linear FEA will be a great deal of help as this is an elastic instability.

http://www.amazon.com/Analysis-Design-Flight-Vehicle-Structures/dp/0961523409

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.