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 how do I calculate bending stiffness for double tubes Post Reply Forum
 Posted by: rdenooij1 ® 12/22/2005, 09:45:37 Author Profile Mail author Edit Can somebody help with the following: I would like to calculate the bending stiffness of a combination of two tubes (of a heart catheter) I have a tube and within that tube there is another tube. The two are not fixed, but the inner tube lies "free" in the outer tube. There is space (air) between the two tubes. I know the geometry and the E modulus of both tubes, and i know how to calculate the bending stiffness EI of the separate tubes. But how does this work with the combination of the two. Where can I find theory about such cases. Thanks, Ruud de Nooij

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 Re: how do I calculate bending stiffness for double tubes Re: how do I calculate bending stiffness for double tubes -- rdenooij1 Post Reply Top of thread Forum
 Posted by: swearingen ® 12/22/2005, 13:08:09 Author Profile Mail author Edit For two beams without shear transfer, when calculating stiffness or stresses, you simply add them together. If both beams had the same bending stiffness, the combined ones would simply have double that stiffness. Yours are almost certainly not the same stiffness, but the concept is the same - just add them.One wrinkle in your case is the space between them. Before they contact each other, the effective stiffness would be just due to the outside tube. Once they contacted, however, you would then add the stiffness of the small tube as well.