Rating a pipe stand
Rating a pipe stand
(OP)
I work out at a mine site, and we have a number of home made stands which are used on our heavy machinery. Most of the stands are constructed using a pipe as the column and then they have a base plate and a top plate. I've analyzed the main column using the Euler, JBJ, and Secant methods for column buckling.
However, I'm struggling analyze the top plate. Most of the stands have a diameter of 6 inches or larger and a wall thickness of 0.5 inches or larger. Then the top plate is simple a 0.75 inch thick plate welded to the top. Some have a caved in top plate where the plate has begun to yield and deform. What is the best method to analyze that top plate to give the stand an overall load rating?
Any suggestions would be helpful.
However, I'm struggling analyze the top plate. Most of the stands have a diameter of 6 inches or larger and a wall thickness of 0.5 inches or larger. Then the top plate is simple a 0.75 inch thick plate welded to the top. Some have a caved in top plate where the plate has begun to yield and deform. What is the best method to analyze that top plate to give the stand an overall load rating?
Any suggestions would be helpful.





RE: Rating a pipe stand
A simplistic approach would be to consider it as a flat circular plate. Depending on whether edge weld is sufficient to transfer any moment you could look at the edge conditions as fixed or simply supported. Roarks and Timoschenko would give you some guidance.
You state that the plate has yielded. In which case the applied load must have transfered to the pipe wall (assuming the object supported is larger than the OD of the pipe). Does this mean that they are still used as a support? In which case the capacity of the end plate is irrelevant. The axial stiffness of the pipe wall will be way greater than the bending stiffness of the end plate.
RE: Rating a pipe stand
RE: Rating a pipe stand
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RE: Rating a pipe stand
RE: Rating a pipe stand
RE: Rating a pipe stand
If you give me all of the pertinent data, I could bang out the calc for you pretty quickly (years ago I wrote a spreadsheet with all of the L's, F's, C's, & G's - for those of you that know what I'm talking about, yes, I was bored).
I have the (outer?) diameter of the pipe at 6", the pipe thickness at 0.5" and the plate thickness at 0.75". Exactly how is the load applied? You said it is a point load, but there is no such thing for 50 tons. I need some sort of footprint to put on the plate. Also, what is the rate of loading? Is it slammed down or let down slowly?
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RE: Rating a pipe stand
Usually for a beam I would use stress=(M*c)/Ix and then knowing the equation for M I could solve for a maximum load. How do I relate the Roark's formula for M to determine the maximum load W? Any suggestions?
RE: Rating a pipe stand
RE: Rating a pipe stand
I don't have access to a 7th edition Roark's, so to be sure we're on the same page, Table 24, Case 9 in my 6th edition is entitled:
Table 24 - "Formulas for flat circular plates of constant thickness"
Case 9 - "Uniform annular line load"
With Case 9a being simply supported and Case 9b being fixed at the edges.
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RE: Rating a pipe stand
The case I'm looking at is:
Uniform load over a small eccentric circular area of radius r0; edge fixed
RE: Rating a pipe stand
Also, the case you're looking at is less conservative than the "Uniform load over a very small central circular area of radius ro, edge fixed" case. If the load is in the center, the moments will be a little higher. Unless, of course, you can guarantee that the load will never be in the center...
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RE: Rating a pipe stand
Thanks again in advance.
RE: Rating a pipe stand
So - the corrections:
1. Eliminate the qr and qt calc lines (B28:G28 and B31:G31)
2. Change the units in G27 and G30 to lb.
3. Formula in F34 should read =MIN(ABS(Wr),ABS(Wt))
4. A small, inconsequential error - the formula in F23 should have 0.675 instead of 0.65
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RE: Rating a pipe stand
Also, as you would expect from the equation for I, your rating will vary greatly by the plate thickness. Capacity more than doubles for a 3/4" plate and a 1" plate gives 4 times the capacity.
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RE: Rating a pipe stand
You said before that moments are given in force-length per unit width. That would of course be (lb*in)/in which is lbs. I guess I'm just hung up on that concept, and I haven't yet found anywhere in the Roark's book that explains this concept.
I guess I'm still missing something. Perhaps you can clear that up or direct me a chapter or passage within Roark's that discusses this.
Anyway, I've just got to say one more time...thanks for all your help and guidance.
RE: Rating a pipe stand
"W = total applied load (force)
q = load per unit area
Mr = unit radial bending moment
Mt = unit tangential bending moment
Bending moments can be found from the moments Mr and Mt
by the expression sigma = 6M/t^2"
So, W is indeed in lb and Mr and Mt are in lb as well (lb-in/in as you said - "unit bending moment"). The 6M/t^2 comes from sigma = Mc/I with c = t/2 and I = bh^3/12 with b = 1 and h = t.
The units do work out - you just have to get used to their convention.
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RE: Rating a pipe stand
Thanks.