Shear Web Buckling - with holes
Shear Web Buckling - with holes
(OP)
Hello learned aeronautical community,
I have been asked recently to allow the creation of a wiring loom penetration in the shear web of a fuselage keel beam in a FAR23 aircraft for which we are the OEM. The proposed penetration is circular, 2" in diameter and located on the beam's neutral axis. The keel beam is around 7" high and the distance between frames is 5.25" in this area.
Problem is that two existing penetrations, of 3/8" and 7/8" diameter, both unflanged and unreinforced, are also in the same shear web. They are not located in any sensible position; i.e. they are off axis randomly placed in the upper right hand side quandrant (if I may call it that) of the web.
I've searched high and low for a paper, method or otherwise evaluating the effect upon a shear web's initial buckling stress of 'random' hole position combinations, which has (unsurprisingly) been unsuccessful.
May I inquire as to whether anyone is aware of (a) some sort of paper or (b) whether I can try and use a linear superposition of other known solutions or (c) I'm headed down some sort of testing/numerical analysis path?
Any input would be greatly appreciated.
Thank you,
Greg
I have been asked recently to allow the creation of a wiring loom penetration in the shear web of a fuselage keel beam in a FAR23 aircraft for which we are the OEM. The proposed penetration is circular, 2" in diameter and located on the beam's neutral axis. The keel beam is around 7" high and the distance between frames is 5.25" in this area.
Problem is that two existing penetrations, of 3/8" and 7/8" diameter, both unflanged and unreinforced, are also in the same shear web. They are not located in any sensible position; i.e. they are off axis randomly placed in the upper right hand side quandrant (if I may call it that) of the web.
I've searched high and low for a paper, method or otherwise evaluating the effect upon a shear web's initial buckling stress of 'random' hole position combinations, which has (unsurprisingly) been unsuccessful.
May I inquire as to whether anyone is aware of (a) some sort of paper or (b) whether I can try and use a linear superposition of other known solutions or (c) I'm headed down some sort of testing/numerical analysis path?
Any input would be greatly appreciated.
Thank you,
Greg





RE: Shear Web Buckling - with holes
RE: Shear Web Buckling - with holes
Otherwise I would agree with Dougt115 your only other option is FEA
RE: Shear Web Buckling - with holes
personally, I'd suggest adding stiffeners to the web, maybe quartering the panel, clearly increasing the shear buckling allowable, and add your hole into one of the panels. adding two per side would be possibly overkill but you could nicely bracket your new hole with stiffeners on 4 sides.
another day in paradise, or is paradise one day closer ?
RE: Shear Web Buckling - with holes
RE: Shear Web Buckling - with holes
RE: Shear Web Buckling - with holes
This is an issue that is still being researched, especially using FE analysis. I agree with SWComposites' approach.
Andries
RE: Shear Web Buckling - with holes
I did feel that FE would be a common suggestion, and being inherently conservative I went along the lines of rb's suggestion and added some additional structure to the web. One motivating factor was that - in answer to rb's question - the shear in the web is not well defined as the original FE model produced in house was a very coarse loads model only.
I also appreciate SWComposites's post regarding calibrating FE models: all too often in my (albeit short) career to date people have blindly trusted FE numbers without having had the model validated or calibrated.
I do thank you all again and often wonder how nice it would be to have another lifetime to be able to devote to learning all one could from read eng-tips posts...
Cheers,
Greg