Anchor forces over several
Anchor forces over several
(OP)
Hello Pipeliners,
Hope I can ask what must be a very basic question regarding anchor forces where I have a number of anchors restraining a line.
Suppose I have say four Anchors as shown below and I calculate anchor forces due to thermal and pressure expansion and find this to be say50lbs for each segment of the line anchor.
Would the total force at each anchor be an addition of the two forces coming from each segment on either side of the anchor or would the forces balance out and cancel each other, making the resultant zero?
[A1]50LB---------50LB[A2]50LB-------50LB[A3]50LB-------50LB[A4]
I hope its not too much trouble.
I used to resolve this kind of question easily with moment distribution when I designed structures several years ago, but not this is not quite the same as moments and I don't want to add the forces if.
Any help would be sincerely and thankfully appreciated
Hope I can ask what must be a very basic question regarding anchor forces where I have a number of anchors restraining a line.
Suppose I have say four Anchors as shown below and I calculate anchor forces due to thermal and pressure expansion and find this to be say50lbs for each segment of the line anchor.
Would the total force at each anchor be an addition of the two forces coming from each segment on either side of the anchor or would the forces balance out and cancel each other, making the resultant zero?
[A1]50LB---------50LB[A2]50LB-------50LB[A3]50LB-------50LB[A4]
I hope its not too much trouble.
I used to resolve this kind of question easily with moment distribution when I designed structures several years ago, but not this is not quite the same as moments and I don't want to add the forces if.
Any help would be sincerely and thankfully appreciated





RE: Anchor forces over several
RE: Anchor forces over several
I can assume the deadweight is negligible , i.e supported by the ground between anchors and the force is from expansion/contraction
Its an hypothetical question to gain insight into how to allocate the forces over the anchors.
Sincerely
RE: Anchor forces over several
RE: Anchor forces over several
The actual amount of the forces I have indicated are hypothetical. I'm wondering if we can consider the forces on either side of the anchor cancelling out and then obtaining a resultant force of zero on an anchor?
What I've seen is people subtracting the forces on either side of the anchor, that is what I'm really trying to understand if that approach is correct?
RE: Anchor forces over several
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RE: Anchor forces over several
In Scenario( A) with Bends/corners between the anchors, its not going to be much of a problem since the bends will relieve the stresses. I believe I will only calculate the anchor force (using the straight lengths just to see what the magnitudes are like. I'll check the deflection and see that it can be absorbed by the legs between the anchor
Scenario (B)is more of a concern.
Assuming the forces on either side appear to balance out, so I believe I'm supposed to subtract but I'm not too comfortable with that mode of thinking.
So if the forces on either side are equal, then hypothetically, the resultant force is .....zero? But I really wonder......
RE: Anchor forces over several
We will design everything from now on using only S.I. units ... except for the pipe diameter. Unk. British engineer
RE: Anchor forces over several
The approach of canceling out of expansion forces on interior anchors is what I am a bit wary about. If this is the case, I don't even understand why even use anchors at all in the interior as guides alone would appear to be sufficient.????
Thanks
RE: Anchor forces over several
RE: Anchor forces over several
I'm only doing the static side of things for now so I didn't think of that
RE: Anchor forces over several
I tend to use substraction-result, assume fluid flow very fast which pipe temperature raise up almost simultaneously.
RE: Anchor forces over several
Anchors are designed to anchor a segment of pipe between them, not for anchoring two adjoining segments. If you design for that force, when the forces happen to balance and cancel out you won't have anything to worry about.
We will design everything from now on using only S.I. units ... except for the pipe diameter. Unk. British engineer
RE: Anchor forces over several
I'd like to beg your indulgence once again on what I thought I had down pat regarding forces and moments acting at end anchors of an L configuration
I have to use the thermal expansion force at the elbow of the L to obtain moments at the end anchors and I'm getting confused about what this force exerted at the bend/elbow of an L configuration would be
Calculating the thermal Force F in say the long leg is quite easy with the well known formula F= A*E*CoefExpansion*(T2-T1) and I think the moment at the short anchor should simply be F*Lenght of the perpendicular short leg.
But when I consider that the deflection imposed by F on the other leg of the L as a guided Cantilever deflection dx = PL^3/12EI from which I can obtain also obtain a P = 12 E*I/L^3
So I'm wondering if the Force I should use to obtain momenst should be
i)F( A*E*CoefExpansion*(T2-T1)) or
ii)should the force be P = 12EI *(dx)/L^3
The reason I'm finding this confusing is that I've calculated F, and P and they are not equal. I expected that they would be equal.
Although I must mention that both legs of the L were given and I merely checked the flexibility and found them adequate.
I'm suspecting that the guided Cantilver is supposed to be used to obtain an opposing leg lenght given an F calculated from the thermal expansion formulae in which case the dx equation of the cantilever would be solved using dx = FL^3/12EI in order to obtain an adequate Lenght for L.
I would appreciate your kind answers.
Yours sincerely but confusedly
RE: Anchor forces over several
The deflection of each leg influences the other by the amount that each pushes the other off their axial alignments, thus creating rotation and the resulting moments due to those rotations. You must first calculate the fixed end moments due to those displacements and rotations, then simultaneously solve for the amount of the combined rotation which will be equal on both members.
I think I mentioned that even the easy ones are not so easy even with a spreadsheet.
We will design everything from now on using only S.I. units ... except for the pipe diameter. Unk. British engineer
RE: Anchor forces over several
Thanks BigInch, I hear you.
I want to use the moment distribution method you mentioned to distribute the end moments (when I calculate it) using the stifnesses of the legs.
But wondering which formulae to use to obtain the end moments, that is if the end moment at the anchor will be obtained from the canteliver displacement dx= Ml^2/12EI or from F*L where my F is the expansion force.
Sincerely
RE: Anchor forces over several
htt
Use the axial growth of one pipe to get the displacement that you will use in the above formula to calculate the fixed end moments of the other pipe.
We will design everything from now on using only S.I. units ... except for the pipe diameter. Unk. British engineer
RE: Anchor forces over several
So the F.E.M is merely 6 EIΔ/L alone?
I think I get the statical indeterminacy and obtaining the displacement Δ as a result of the thermal expansion as well as the thermal expansion force is very easy
I was confused into thinking maybe i needed to use F*L and 6 EIΔ/L
So in doing my moment distribution e.t.c I will use the F.E.M as simply 6 EIΔ/L?
Thanks
RE: Anchor forces over several
I forgot I had already suggested moment distribution. That is a good way to solve this problem, so it's a good thing you remembered and chose to use it.
We will design everything from now on using only S.I. units ... except for the pipe diameter. Unk. British engineer