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,

 

[rb1957]

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

 

[KingOfStress]

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.

 

[rb1957]

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.

 

[bf109g]

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

 

[SWComposites]

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.

 

[GBor]

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.

 

[KingOfStress]

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).

 

[MNLiaison]

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

 

[KingOfStress]

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.

 

[Lcubed]

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

 

[rb1957]

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

 

[KingOfStress]

I have found a good document about our topic as attached. Is anyone having this kind of document in aircraft industry?

Thanks for your help

 

[rb1957]

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

 

[KingOfStress]

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?

 

[GBor]

KingOfStress,

When you want to quote someone, use the TGML command for quote, which is

, and end it with a '/quote' command in brackets. Bolding everything looks like you are irritated.

 

[KingOfStress]

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

 

[rb1957]

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

 

[RPstress]

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.

 

[40818]

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.