Design of Flat Plate Beams to AS4100

[James_Gleeson]

Can a flat plate beam be designed using as4100? If so, say if we have a 200mmx10mm plate bending about its major axis, what values for d1 (clear depth between flanges), tf (thickness of critical flange) & tw (thickness of web) would you adopt for use in table 5.6.3 (A) twist restraint factor?

 

[SteynvW]

Under certain loading and structure conditions yes, and with others you have to take a detour first.
Now bending where the top flange is unsupported, cannot be done with 4100 straight away, and a buckling analysis has to be completed first and the section analysed as a compact section if it is not close to buckling.

 

[James_Gleeson]

Hey SteynvW, thanks for the response. Do you know of any worked calculations online that I could have a look at to go through the specifics in a bit more detail?

 

[Retrograde]

This advisory note discusses the problem (in terms of BS EN 1993-1-1)

https://www.steelconstruction.info/images/3/3f/AD-391.pdf

 

[James_Gleeson]

Hey Retro,

Thanks for sending that through, although I haven't had a chance to look at it properly it looks to be a good document. I welcome any additional documents/comments anyone else might have, the more info the better. Appreciate the help guys.

 

[bugbus]

One issue seems to be that there is no way of classifying the section compactness in AS 4100 (or AS 5100.6 for that matter).

The closest category seems to be "Maximum compression at unsupported edge, zero stress or tension at supported edge". But obviously the bottom of the plate will not be supported.

Another approach is to consider that the plate has similar load and restraint conditions as the top half of an ordinary beam web, and then assess the compactness by doubling the effective height and comparing it to the category normally used for a beam web ("Compression at one edge, tension at the other"). But this is just a guess, probably not a reliable way of checking it.

For the twist restraint factor, I'm not sure what you would do there. But realistically, I don't think you could rely on any sort of restraint condition other than FF to get any meaningful strength out of the plate in bending. In other words, I would think that you would need to have the plate bolted or welded along its full height at either end to provide that full twist restraint.

 

[SteynvW]

What bugbus is refering to is exactly the problem, a plate cannot be defined into one of the 3 section compactness classifications, hence a quick shell buckling analysis to determine if you can use "Compact" section modulus.

 

[James_Gleeson]

Hey guys,

Thank you very much for all this great information. StevynvW, sorry for my lack of understanding but by buckling analysis, can you please confirm what part of the code you are referring to? 5.6.4/Appendix H? 4.6? Appreciate the help.

 

[Agent666]

Check clause 5.2.2.3 and think about what that actually means.

Sections such as narrow rectangular members are treated as being compact. Their capacity is governed by lateral torsional buckling before local slenderness effects become relevant.

Just consider as compact and follow normal member design rules, evaluate alpha_s as per normal for any other section type.

https://engineervsheep.com

 

[BJI]

I believe the 5.2.2.3 clause is only in NZS 3404 not AS 4100 but the reasoning behind it is equivalent.

 

[Agent666]

Yeah should have looked. But agree that's the intent for AS4100 either way.

https://engineervsheep.com