Problem regarding +YROD having displacement in vertical axis

The model consists of steam piping laid over the pipe rack operating at temperature of 495 Deg.C from WHRSG boilers to common steam distribution header with a tapping in between to process . We have modeled the piping with expansion loops to take care of stress requirements and rod hangers, where the horizontal displacement is more than 140mm. In the restraint summary of the model, we have noticed that the +YROD at few node numbers are loaded with force in 'X' & 'Z' axis with a displacement in 'Y' (vertical) axis, in spite of increased rod length, rod tolerance & change in rod increment.

For example, the said problem is with the rod hanger(+YROD) at node 1300, where the displacement is X= -155mm, Y= -4.894mm & Z= 50.765mm. However at few node numbers we have observed that in spite of large horizontal displacement the above explained problem does not exist.

It is also not clear to us, why the vertical displacement is appearing in the displacement summary for the rod hangers(+YROD) which has the above problem and this displacement varies with the change in rod length. Please clarify.

Uday
I do not know why you are getting strange result in your system.
But I thought as at node no 1300 you are getting heavy X & Z movement so you should get +4.894mm vertical movement instead of -4.894mm vertical movement from simple geometry.
You can also check the restrain summery whether at node 1300 operating load is -ve or +ve.
In our system where ever we find +ve rod hanger load at operating condition we replace that with spring hanger or find some another location for support.

check the swing angle of your rods where you are getting large horizontal loads an angle greater than 4 degrees is considered to be excessive....

What's your input for rod length? (Vertical) rod length and horizontal displacement determine the rod swing up or down. Use rod length and net horizontal displacement to establish swing angle. Then lay the rod length on that hypotenuse to find the vertical lift.

+YRODs swing up and -YRODs swing down. +YRODs carry a -Y load and -YRODs carry a +Y load. [Previous sentence is incorrect - removed Aug 2016.] If you do not specify + or - in the input, C2 sets the ROD positive. The vector points to the pivot point. Its easy to talk about YRODs here but the same rules apply to any vector.

I agree with shr, your -Y displacement doesn't sound good with a +YROD.

I would think that the B31.1 rule of a 4 degree max rotation (as John Luf points out) would allow most of these rods to be modeled as simple Y restraints. Any other opinions?

Sir i have increased the ROd length upto 10m but still that problem exists. I have also noticed that at some nodes where the horizontal displacement is more than the node at 1300 its not taking load in X and Z axis. I have changed the swing angle still this problem exists. Should i model these +YRod which i have problem as Y restraints thats what u meant.I have given a Rod tolerance of 5.

Shall i send the model for you to know clearly whats the problem im facing so that u can suggest me what to do.

Check: You're trying a ten meter rod length in your calc? That doesn't appear realistic for real-world (simple rod) hangers.

Uday,

Please send your Caesar II model (.c2) to techsupport@coade.com and we will look at it.

So Loren whats the rest of this story???... Don't keep us all swing on a Yrod.

I still have not received any files from you Uday. I need to see the details of your input to find the mistake. A Yrod, or +Yrod cannot have a negative displacement, EXCEPT in the EXP case or any other combination case. For the EXP or other combination case the results are not displacements, but delta-displacements and can be any sign as the represent the difference between or the addition of two other load cases. I suspect this is what you are looking at. Your OPE and SUS cases should not have a negative displacement at the Yrod location.

Loren Brown,

Based on your request i have sent the model to techsupport@coade.com please reply as soon as possible.

At this point I don't know how you got negative displacements at your +YRod locations. I could not reproduce this. Using your file I got all positive Y-displacements.

Just to finish the story: The file I received did in fact have a negative displacement in the OPE load case. But when I ran the file the displacements were indeed positive or zero. How Uday managed to get negative displacements I don't know and I cannot reproduce it, but suspect it had something to do with the rod tolerance settings in configure/setup that must not have had enough fidelity and allowed convergence with a small negative displacement.

Secondly, I reviewed the resultant rotations for all load cases and all of them were smaller than 1 degree. This means that there is no reason for you to use the YRod restraint type at all! Far better that you model rigid Y restraints as the results will be accurate, perhaps more so than using the YRod restraints as there is a special iterative procedure required with the large rotation rods. Y restraints will not cause convergence problems, which is important because when convergence is not obtained you must adjust convergence criteria in configure/setup and that always introduces some error into the solution.

I also face same problem in our organization while working with expansion bellow few days back . In my pc file was showing absolutely fine result but same caesar file was showing some strange result in my friends computer.
I could not detect the error & finally reinstall Caesar software in my friends pc once again then the problem was solved.
Uday you can do the same & check .