Hello all,

I was hoping someone could give me some advice.

I have piping linking two separate structures supported via a bridge. The bridge is fixed to one structure but sliding on the other side, as a result there is quite a bit of movement in the bridge (relative to the piping). As the piping is resting freely on the bridge it is free to slide in X, and Z and should only see frictional forces from movement in these directions but all displacements in Y (of the bridge) should be transferred onto the piping.

I have tried to model this by representing the bridge as ridged vertical elements (placed where each beam of the bridge would contact the piping) connected through CNODE to the piping. All the vertical rigids are tied together through horizontal rigids, I then fix one end of my "bridge" and apply my displacements to the other. This works well for the Y displacements but all X and Z are transferred to the piping as well. Any suggestions on how to model the piping "sliding" on the bridge?

Hi Mholt
If I understand your model correctly.
There are 3 rigid below pipe. one vertical rigid & two horizontal rigid like a reverse T
In horizontal one side put anchor. other side put bridge displacement.
& in vertical rigid where rigid is connecting with pipe with connecting node put Y support only.
Like if node point at pipe is 50. Put support 50 +Y only with connecting node 51.vertical rigid node start with 51.

Best of luck.

Thanks shr,

This is similar to what I had done, with a few key differences (where you applied the +Y).

Works well.

Bridge piping is checked for fatigue due to waves. The piping is analysed with one end fixed and other end with the displacements, for example there are two platforms interlinked with bridge, pipe running between these two platforms via bridge. Specify in your model the fixed end and displacement at the other end where bridge ends and check for displcaement stresse and fatigue as well. You might require good size loop on one of the platform to accomodate the displacements depending on your pipe size and thickneses, material etc. If your doing this type of analysis get help of anyone who has done analysis earlier for bridge piping. You might need to consider the wind as well so the need of guides on the bridge.

As PKU has suggested you would require a Fatigue assessment as well. Refer PD 5500 for more guidance.

Cheers