Fasteners - Frusta and Member Stiffness

[garyyuen42]

Hi All,

Done some reading one bolt joints which seperated in the bolt stiffness and the member stiffness. Generally text books mentioned the theory of the Frusta and calculate the memeber stiffness. What happened when the are is not sufficient for the frusta to exisit in its normal manner? I have attached picture for reference. Shown a 20 x 20 hollow section on one of the faces there is a tube inserted. Then we have washers on both side with bolt through the middles and a nute on the other end.

Any ideas?

 

[desertfox]

Hi garyyuen42

If it were my joint I would just consider the bolt preload divided by the cross sectional area of the inserted tube.
Your sketch doesn't show what it is your fastening together so I don't know what the stiffness of the mating part is.
Only if the tube that is inserted into the hollow box section is slightly longer or perfectly flush with the outer faces of the box section can it be considered to take the bolt preload.
If the tube is shorter than the box section then it may deform the box section untill contact with the tube is made.
Can you give anymore information.

 

[dhengr]

Gary:
I think you really need to pick up a few text books on Engineering Mechanics, Strength of Materials and Machine Design. And, do a much better job of sketching and describing your problem. Your dimension “l” is neither the height of your hollow section, nor the length of the tube, and just doesn’t seem to make much sense. As Desertfox suggested: If the length of the tube is greater than the height of the hollow section, the bolt and nut will just act on the tube as if it were a hollow compression member; if the length of the tube is shorter than the height of the hollow section, then the flexural stiffness of hollow section top and bottom flanges will come into play until they deflect enough to bring the tube into play. Then the tube and the hollow section flanges will counteract the bolt forces together. I don’t think there are any frustra in your joint sketch. If you don’t mind my saying so, your dwelling on the term “frusta” is ‘frusta...rating’ your understanding of the problem.