Floor Beam Fixity data for Boeing Aircraft?

[joekm]

I'm in the middle of evaluating a structural modification to install some extended first and business class seating to a Boeing 747 (upper and lower deck). We are, of course, working conservatively but I'd prefer not to make unnecessary mods to primary structure.

I ran across some floor beam fixity data for a B757 (generally around 40%), but I was wondering if anybody had similar data for the B747 that was "blessed by Boeing" as it were?

Thanks

Joe

--
Joseph K. Mooney
FAA DER Structures

 

[compositestress]

There is little data available for floor fixity on older A/C. You could use the values for 777 (similar size)ie rotational stiffness = 6,000,000.
By the way I am working on a 737 - same cross section as your 757. I have seen 50% used for frame fixity. I guess by 40% fixity you mean to use a value of 40% of the bending moment at the frame for the fixed condition as the bending moment in the frame due to floor loading???

 

[GregLocock]

More generally it is hard to get more than 60% without using a carefully designed joint. With care it is possible to get >90%, but they may not be economic, or of any functional value.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[rb1957]

if you could live with it (wihtout unnecessarily complicated or extensive mods) why not assume fully fixed when analyzing the ends, and simply supported when considering the mid-spans ? (ie the worst of all worlds)

 

[joekm]

Thanks to all, that's kinda what I would guess as well.

rb1957 - That's what we wound up doing, I was just hoping to minimize impact to the overall structure. Got a 767 coming up and we are just going to model the whole sha-bang.



--
Joseph K. Mooney
FAA DER Structures