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Hand Calculation of Frame Webs with Flanged Hole

Hand Calculation of Frame Webs with Flanged Hole

Hand Calculation of Frame Webs with Flanged Hole

(OP)
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,



 

RE: Hand Calculation of Frame Webs with Flanged Hole

my liege,

i believe there is very little written on this subject.  Our sage, the most venerable Bruhn, has only a short comment (chapter C10.18).

if i could submit an idea for your consideration, my liege, you could ...
1) ordain that the web reacts only shear loads and the caps (even if they are formed flanges) take the compression and bending loads; or
2) consider the flanged lightening hole is no less effective than a plane web (without the flanged hole) for which there are many calcs.

your humble subject

RE: Hand Calculation of Frame Webs with Flanged Hole

(OP)
First of all, I would like to thank you for your reply.

I know these two options, but especially for the second one how can you decide a flanged hole is more effective than plain web. This is the main question for me.


 

RE: Hand Calculation of Frame Webs with Flanged Hole

check the web net area shear allowable ... Fsu*(h-D)t

i suspect that a flanged hole increases the allowable shear in a web ... compare Bruhn equation C10.18 with the standard flat web in shear.

this supposes that you're happy to allocate the different loads to different pieces of the structure; your original question is a very difficult interaction that i suspect is only experimentally based.

RE: Hand Calculation of Frame Webs with Flanged Hole

O great one,

A flanged hole is indeed more effective than a plain web in shear.  A quick glance of my Boeing material shows that unreinforced holes in webs are to be kept less than 5% of the cross section of the web and within h/8 of beam centerline.  In other words, small system relief holes are OK close to the center of the web.

As far as determining just how effective flanged holes are, I believe that there would have to be testing done.  The airframers have generally done their own testing with parts flanged to their design standard.  My Boeing material has this data.

Lacking the test data, you would have to go with the worst case and consider the web as a plain web as rb says.

your loyal serf  

RE: Hand Calculation of Frame Webs with Flanged Hole

If you are just concerned about web stability, then you can probably determine the effectiveness of the flanges using detailed FE models.  If you are concerned with web strength, then you probably need test data to validate the design.
 

RE: Hand Calculation of Frame Webs with Flanged Hole

The marine industry (particularly military) does quite a bit with material replacement...using flanges to provide equal strength for bulkheads with holes cut through them.  I know there is a calculation method...I just don't remember where to find it, but it may just be that we are looking in the wrong industry.  I know it doesn't take much of a flange to result in equivalent strength.

RE: Hand Calculation of Frame Webs with Flanged Hole

(OP)
When I did some stability comparison (using FEM) the web with a flanged hole and a plain web under pure compression. The results are changing depends on flange stiffness (at hole edge).


 

RE: Hand Calculation of Frame Webs with Flanged Hole

Check out the following document, NACA WR-L-402, "The Strength and Stiffness of shear webs with and without lightening holes". Tests were performed on holes with no edge reinforcement, flanged reinforcement and beaded reinforcement and the effects of can be compared.


Regards
 

RE: Hand Calculation of Frame Webs with Flanged Hole

(OP)
MNLiaison (Aerospace)      
6 May 08 23:18
Check out the following document, NACA WR-L-402, "The Strength and Stiffness of shear webs with and without lightening holes". Tests were performed on holes with no edge reinforcement, flanged reinforcement and beaded reinforcement and the effects of can be compared.

Yes I know this document, but if you read my question again you can see that I am looking for a solution for combined loading.
 

RE: Hand Calculation of Frame Webs with Flanged Hole

Exalted one:
It is written that the equations of failure for buckling under combined loads are:

Shear and Compression: Rs2 + Rc = 1.0
Shear and Bending: Rs2 + Rb2 = 1.0
Bending and Compression: Rb1.75 + Rc = 1.0
(the numbers following the ratios are the powers to which the ratio is to be raised; I didn't know how to do a superscript for this submittal)

Reference: Niu, Michael Chun-Yung, Airframe Stress Analysis and Sizing, First Edition, October, 1997, Hong Kong Conmilit Press, Ltd., Hong Kong, Section 11.5

Regards
Lcubed

RE: Hand Calculation of Frame Webs with Flanged Hole

L^3,
these are the standard interactions for stable sections, probably not applicable to webs, let alone webs with flanged lightening holes.

my liege,
i don't think there is much out there for combined loadings on webs with flanged lightening holes; i thought we were going down the path of assuming the different loads were reacted by different parts of the structure).  

i think that you can show that either ...
the web is stable in shear buckling (using Bruhn C10.18) and the compression cap is stable; or
use C10.18 to show that it is conservative to ignore the flanged lightening hole, and treat the web as a plain web.

your loyal minion

RE: Hand Calculation of Frame Webs with Flanged Hole

but like the paper says ... webs with holes under compression ... not the interaction you were looking for

RE: Hand Calculation of Frame Webs with Flanged Hole

(OP)
rb1957 (Aerospace)      
7 May 08 17:47
but like the paper says ... webs with holes under compression ... not the interaction you were looking for

Some method says that web can carry the only shear forces and inner and outer caps can carry only axial forces and bending moments. I have added this document in order to improve the assumption is not sufficient.

Therefore, if anyone has a solution for combined case, could you assist me please?

 

RE: Hand Calculation of Frame Webs with Flanged Hole

KingOfStress,

When you want to quote someone, use the TGML command for quote, which is [quote], and end it with a '/quote' command in brackets.  Bolding everything looks like you are irritated.

RE: Hand Calculation of Frame Webs with Flanged Hole

(OP)

GBor,
Thank you so much your concern. I will use this option after that.

 

RE: Hand Calculation of Frame Webs with Flanged Hole

i guess by now the answer to the original question is "no".   

RE: Hand Calculation of Frame Webs with Flanged Hole

ESDU 02.04.05 gives interaction curves for shear and bending/endload for onset of buckling for no hole. As a first approximation I'd use the same ratios but with the critical buckling loads for each mode as those for holed plates.
 

RE: Hand Calculation of Frame Webs with Flanged Hole

I think Airbus has some data regarding this subject, and it's origins stems from the days of the BAE stress office reports. I will try to remember to have a look through my stuff tomorrow for you.

RE: Hand Calculation of Frame Webs with Flanged Hole

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?

RE: Hand Calculation of Frame Webs with Flanged Hole

(OP)
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.
 

RE: Hand Calculation of Frame Webs with Flanged Hole

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).
 

RE: Hand Calculation of Frame Webs with Flanged Hole

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

RE: Hand Calculation of Frame Webs with Flanged Hole

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.

RE: Hand Calculation of Frame Webs with Flanged Hole

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

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