Hand Calculation of Frame Webs with Flanged Hole

[KingOfStress]

Hello, to All,

Question: How can I solve the stability of the frame webs with flanged holes under combined loading (Shear + Bending + Compression)? Is there any hand calculation method for this problem?

Thanks,

 

[Miner89r]

I believe that Boeing Design Manual (BDM-6520, Figure 4-8) has the interaction curves you are looking for. Interestingly the EXACT same figure can be found in the Bombardier Strength Manual which leads me to believe that they must have copied it from some publicly available document. Does anyone recognize were it came from?

 

[KingOfStress]

To RPstress and Miner89r,

Firstly, I would like to thank you gentlemen.

I know the documents that you said and unfortunately there is no information about web with flanged holes in these resources.

To 40818,

I hope you can find the report that you told us.

 

[40818]

Sorry about the delay.

Havn't quite found what your looking for i'm afraid. The concept of the interaction formula is generally the way it has been resolved. The generalised interaction formula i believe comes from General Dynamic Structures Manual. RB1957 gave in hos first reply the general assumption.
Anyway, there are many ways of skinning a cat, and one method is to use ESDU81047 which has an accompanying program A814V40, which provides a method for calculating elastic buckling loads of flat rectangular plates under combinations of uniform in-plane biaxial and shear loads. I think the "black-box" methodolgy within it stems form the BAE stress office report data regarding the elastic buckling ratio's etc.
When you have a hole within a panel you have to use a bit of judgement regarding its effect. If its a small hole at the centre your not really going to see much in the way of bending. Panels with holes (reinforced or flanged) can be regarded into 2 classifications: large cut-outa and small cut-outs. In the case of a large cut-out with a reinforcement that extends the width of the panel, the featrue can be considered to act as a panel breaker, reducing the panel aspect ratio of the analysed panel. For a panel with smaller cut-outs, the feature can be accounted for by assuming a plain panel of reduced thickness. the equivalent thickness can be determined by discounting the thickness by a factor of area of the hole to that of the plain panel, (see ESDU 84042).

The panel edge fixity i think is more critical to the overall instability of the panel. The compressive loads will therefroe tend towards the edge members leaving the shear in the web. Towards the cente of the panel shear dominates, but at the corners you can see the combinations of bending, shear and compression, though if you reach an overall panel critical buckling load based upon a (say) Von-mises stress at a corner how do the 2 relate to each other??

I think its more of a black art than a science, because of the effects of the differing perameters involved.

Not much help to you i'm afraid. You could create a detailed NLFE for the elastic buckling, and even maybe NIKE3D for the post-bukling effects. And validate them against various previous methodologies for simple inputs (i.e pure shear etc).

 

[Lcubed]

Sorry I've been out of touch.

rb1957, these are the interaction curves/equations used to provide margins of safety, or margins of deficiency, for the failure mode of buckling of a flat plate. Stable sections, by which I mean sections which do not fail by buckling or crippling, are analyzed using different equations/curves. I think you may have misread my submittal, or may have a typo in the reference you are using.

Regards
Lcubed

 

[rb1957]

L^3,
they may be interactions for the onset of buckling of a flat plate (and one without a flanged lightening hole), but the ultimate margin is much higher, considering diagonal tension effects, etc. personally, i think flat plate solutions are relevant to a plate with a "proper" flanged lightening hole, but the OP seems to want to press for his specific solution, whihc i don't think is out there.

 

[Lcubed]

rb1957,
I see. I was just responding to his request for interactions; I haven't tried to find a method for obtaining the actual stresses. I doubt that any interaction approach would work at ultimate, for the reasons you just stated.

Since buckling at limit is usually not acceptable where the web is penetrated, I think the OP could use interaction for limit, but if he cannot find the limit load stresses with reasonable accuracy, there is no need for the interaction equations.

Regards,
Lcubed