Restraint Loads for Structural Engineering

Question

Restraint Loads for Structural Engineering

phinn (Mechanical)

(OP)

2 Oct 16 11:32

Hello,

our structural engineer asked me a question on the piping restraint loads he received from the pipe stress analysis, I am not 100% sure on the topic so I hope someone has encountered the same question:

The pipe restraints (in Caesar as well as Rohr2) are usually placed on the pipe centerline, and therefore the results at these restraints reflect the loads at the pipe centerline. Now my colleage who is engineering the steel structure says he needs the loads at the bottom of the the pipe shoe (interface between steel structure and shoe).
At first thought it made sense to me, but I would have to add rigid elements to each and every pipe restraint in the hight of the pipe shoe to achieve this. I guess he wants to know the moments that are caused by the force x shoe hight..

What do you guys say to this? Have any of you encountered this question?

DSB123 (Mechanical) · Answer 1 · 2016-10-03 08:04:03

The only issue is where you have a guide or a linestop or an anchor point. Then the distance from the pipe centreline to the underside of the shoe has to be considered. For simple supports the restraint load at the centreline is the same as at the shoe to steel interface. Also remember that for a guide/linestop/anchor where moments come into action the "local" loads applied to the pipewall need to be considered in conjuction with the other stresses due to pipe span/pressure/thermal loads.

phinn (Mechanical) · Answer 2 · 2016-10-03 13:37:48

Hey thanks for taking the time

When I add "regular" pipe restraints, such as Guides, Axial Stops etc. to the center line in the form of pipe shoes the standard for me, and from what I've seen so far is, that only the translational degrees of freedom (x,y,z) are fixed and the rotational (rx,ry,rz) DOF are free. That way naturally I have no moments as result.
If a line stop is achieved by adding plates to the steal structure (and not by welding the shoe to the steel structure), I would only expect shear forces acting on the beam.

Would you say that if a line stop or a guide is placed, the rotational DOF should be fixed?

BigInch (Petroleum) · Answer 3 · 2016-10-11 08:52:19

Line stops and guides are typically taken as directional restraints only, so no moments are generated in the pipe that would need to be transferred to supports. Stops and guides should therefore act as they have a pin between pipe and structure, even if they actually don't, so they will not be able to transfer any significant moment from pipe to structure, or structure to pipe.

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Restraint Loads for Structural Engineering