Aluminum/Stainless Steel Tubing Strength
Aluminum/Stainless Steel Tubing Strength
(OP)
Sir/Madam,
I am not an engineer. I am a retired banker and I was hoping that you might point me in the direction that would help me solve a vexing problem.
I live on my 46' ketch and have devised a way of securing my dinghy that requires the use of either aluminum tubing or stainless steel tubing. My problem is that I cannot find a reference the formula for determining the strength of these items.
For example: assume you have an aluminum tube that is 8' feet long, one and one-half inches in diameter, with a wall thickness of one eighth of an inch. If you attach a band of material (webbing, for example) that can support 1000l pounds, what dimensions are required for the aluminum tube that will support a load of 300 pounds?
If you have read this far, I thank you. I am not looking for an answer to that specific set of measurements, but, for standard quality aluminum/stainless steel, what is the formula for determining the proper tubing to use? Is there a set of reference tables that one can use to come up with the answer to any length of tubing, weight, etc.
I have searched the internet trying to find formuli or reference materials, to no avail. Any help that you can render would be much appreciated.
Thanks and Regards,
Dutch Huffman
gunshipdutch@aol.com
I am not an engineer. I am a retired banker and I was hoping that you might point me in the direction that would help me solve a vexing problem.
I live on my 46' ketch and have devised a way of securing my dinghy that requires the use of either aluminum tubing or stainless steel tubing. My problem is that I cannot find a reference the formula for determining the strength of these items.
For example: assume you have an aluminum tube that is 8' feet long, one and one-half inches in diameter, with a wall thickness of one eighth of an inch. If you attach a band of material (webbing, for example) that can support 1000l pounds, what dimensions are required for the aluminum tube that will support a load of 300 pounds?
If you have read this far, I thank you. I am not looking for an answer to that specific set of measurements, but, for standard quality aluminum/stainless steel, what is the formula for determining the proper tubing to use? Is there a set of reference tables that one can use to come up with the answer to any length of tubing, weight, etc.
I have searched the internet trying to find formuli or reference materials, to no avail. Any help that you can render would be much appreciated.
Thanks and Regards,
Dutch Huffman
gunshipdutch@aol.com






RE: Aluminum/Stainless Steel Tubing Strength
Assuming fabric strap is located at tube midspan, compute M = PL/4, where M = bending moment at tube midspan, P = applied transverse load (300 lbf in your example), and L = tube span length (96 inch in your example). Compute tube moment of inertia I = pi[D^4 - (D-2t)^4]/64, where D = tube outer diameter (OD) and t = wall thickness. Compute tube bending stress sigma = 0.5(M)(D)/I. Compute tube margin of safety MS = {Fty/[FS(sigma)]} - 1, where FS = factor of safety. A typical value for FS is FS = 1.67. If MS is zero or positive, the selected tube and material are adequate to resist the bending stress. If MS is negative, select a larger or thicker tube cross section and/or a stronger material and repeat the process until MS is zero or positive. Good luck.
RE: Aluminum/Stainless Steel Tubing Strength
RE: Aluminum/Stainless Steel Tubing Strength
RE: Aluminum/Stainless Steel Tubing Strength
Aluminum Structures, a guide to their specifications and design.
J. Randolph Kissell, Robert L. Ferry
Wiley Interscience
a very good book. To do anything well takes no less than what there said.
Out of memory of what there read (I am not aluminum structures designer), in any case typical aluminum structural alloys seem to be a bit less strong than 36 ksi steel, the shear modulus is quite lower, and safety factors for strength were in the vicinity of 2, what would give for pipes in only bending about 16 ksi, but depending on the alloy.
http://www.euro-inox.org/e/frames/main/fp.html
gives a pdf on design of stainless steel structures.
Note that sizing structural members is subject to many things, and so is always better a professional looks at the thing.
RE: Aluminum/Stainless Steel Tubing Strength
This other has typical properties of some stainless steel
http://www.aksteel.com/markets/pdf/12_SR_data_sheet.pdf
RE: Aluminum/Stainless Steel Tubing Strength
RE: Aluminum/Stainless Steel Tubing Strength
(1) You have a tube supported at each end of, say, a 96-inch span length with no other supports in between these two span end supports? (2) You have one or more webbing straps attached transversely (perpendicularly) to this span, and each strap has a tensile capacity of 10001 lbf? (3) How many webbing straps are attached within the given span length? (4) If there is more than one strap per tube span, do the straps have any characteristics such as uniform spacing, symmetry of attachment locations relative to midspan, etc? (5) If there is more than one strap per tube span, does each strap carry the same applied load P (simultaneously)? Or do the applied loads vary from strap to strap? (6) Can the straps significantly slide longitudinally along the tube? (7) Will each strap load be applied slowly, gradually, very gently, and monotonically? Or could a load be applied suddenly? (8) Are the tube supports completely rigid connections? Or can the tube span ends rotate even a small amount in or at the supports (and I am not referring to the tube spinning about its own axis here but instead to any minute rotation about the other two axes)? (9) If the tube ends can rotate even a small amount in the span end supports, is the tube cut at the 96-inch span ends? Or is it continuous into an adjoining span at each span end? (10) What is the width of each strap?
RE: Aluminum/Stainless Steel Tubing Strength
RE: Aluminum/Stainless Steel Tubing Strength
Minimum Rupture Tensile Strength .... from 20 to 45 ksi
(more typical 30 to 37 ksi)
Minimum Yield Strength 7 to 36 ksi
(more typical form 20 to 29 ksi)