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istambul (Aerospace) (OP)
29 Aug 12 16:18
Hello Everybody,

I am doing hand calculation for the fasteners. Please find attached picture for reference for loading. The flexible beam is attached to relatively rigid structure. I believe the fastener fail due to bending not by axial tension alone. Hence to extract the fastener loads I have used the following approach.

1. Tension loads in fastener are taken from the reactions

2. For shear load extraction, I have considered beam as clamped beam at both the ends. Then I calculated the end moment at the supports. The end moment is equated to couple across the thickness of the beam. The couple is shear load

First of all I would like to know whether my approach correct. If not, is there any other way to calculate the fastener loads?
Thanks in advance.
SAITAETGrad (Aeronautics)
29 Aug 12 21:02
All analysis involves levels of abstraction and idealization. Your model does not consider the flexibility of the fasteners or prying action. Your analysis is linear. You have idealized a beam and not a web/plate. The assumptions may be reasonable for your situation dependent on the real world model. What you need to determine is if your idealized model sufficiently bounds your uncertainties. If not, you may want to make overlapping assumptions and/or model refinements. For joint loads, your analysis is likely conservative (maybe not if beam pries on fasteners). But, for the beam bending stress at the center your fixed ends push the internal bending moment down. A simple set of overlapping assumptions could be to analyze both ss and fixed.

There are many references for joint and beam analysis.
Helpful Member!(2)  rb1957 (Aerospace)
30 Aug 12 8:16
my 2c ...
1) you're underestimating the peak tension by ignoring the moment that'd probably develop. of course if the loaded plate is very flexible then the outer row of fasteners are probably ineffective.

2) if the loaded plate is Very flexible, then it could be expected to develop hoop stresses. i'd use this to determine shear at the fasteners. I understand your thougt about using a fully restrained beam, but i think that'll under-estimate the shear force if the plate behaves like a membrane. it's reasonably easy to calc the deflection of the flat plate by linking the strain in the plate (from hoop stress) to the change in length as the plate deflects to a radius R.

3) you then have to consider carefully the plate at the edge, near the support ... will the plate continue as a membrane (lifting off from the support plate between the fasteners) ? does the support plate provide a fixed (non-rotating) support to the plate so there is a change in curvature of the plate and moments in the plate and at the support ?

4) draw a free body diagram, showing how you balance the in-plane membrane stresses with the reaction forces. personally, if the membrane is that flexible i think you'll get more mileage out of the fasteners if you stagger the pattern.
istambul (Aerospace) (OP)
31 Aug 12 0:03
Hi rb1957,

Thank you for your suggestions! It solves my problem. Have a nice week end!

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