Pipe Bridge - Sliding Connection

[KingKongdoor]

I'm designing a pipe bridge to span from a tank farm platform to a process building. Wanted to see you guys thoughts on a sliding connection with teflon bearing pads.

Info...
The bridge is two truss members built up with double angles and braced together. Top chord bearing
Bridge span ~50ft
Tie-in Height at building and tank farm pipe structure ~40ft
Tank farm platform is not attached to tanks other than the process piping.
Process building is approx 60ft tall with a ~120'x90' footprint, steel moment frames with a ~30'x15' grid(I would prefer a smaller column spacing but not my call)
The building is fully enclosed

My concern is differential movement between the tank farm structure and the process building. Based on preliminary analysis I could have 2" of movement between the two structures at the bridge height during a wind event(120mph).
My gut says the bridge will be fine no matter the connection and the tank farm structure is flexible enough at that height to take the movement. I can calculate and design for the axial load that could be applied to the bridge and structures.

I however plan on designing the bridge to have a pin connection at one end and a sliding connection at the other end with teflon bearing pads. I will then determine how large of an axial load would start causing a problem in case of a sliding connection failure or a movement worst than the results of my analysis. I would go heavier on the steel if needed. I prefer not to have a sliding connection on each end.

Does this sound reasonable to you guys or am I overthinking the problem?

 

[SlideRuleEra]

I however plan on designing the bridge to have a pin connection at one end and a sliding connection at the other end with teflon bearing pads.

IMHO, that's all you need. I first used teflon bearing pads for an elevated walkway in 1986. The walkway is between two industrial structures (electric generating units) that move a significant amount during operation and do so independently. Fifteen years later (2001) the system continued to perform as intended. Just be sure to constrain the sliding motion from side-to-side movement and uplift.

http://www.SlideRuleEra.net

 

[dhengr]

KingKongdoor:
Do some thinking about the various movements and magnitudes in all directions, and design for them in their order of magnitude, worst movement getting the primary attention. But, as SRE suggests guide and limit them in some way, so you can design around and manage them. Obviously, you should not have slides at both ends, or the piping would be stressed in pushing or holding the bridge in place and you don’t want that. Just as obviously, the bridge is not pinned in every direction at the one end. Smaller movements and their accompanying forces, moments, etc. must be designed for. Put the Teflon pad on the bottom facing up, and the polished/chrome plated bearing surface on the top and facing down. The top stl. pl. must be large enough so that it always covers the Teflon pad, for all movements, so that the Teflon is less likely to get contaminated. Maybe even provide a dust skirt, and/or scrapers, around the bearing. You do not want that joint collecting grit and grime and taking it into the bearing surfaces.

 

[KingKongdoor]

Thanks for the input guys! I want to allow controlled movement and of course the last thing I want is forces transferring into the process piping. I'm not designing the piping or their connections but I will confirm that they are allowing for movement in their design.

 

[WARose]

Thanks for the input guys! I want to allow controlled movement and of course the last thing I want is forces transferring into the process piping. I'm not designing the piping or their connections but I will confirm that they are allowing for movement in their design.

That's what I would be talking to them about. A few inches of differential movement isn't that unusual. I would get with your piping group and ask if the pipe can accommodate the displacements you are seeing before I went with Teflon bearing plates. A lot of times they can handle it. (Depending on the pipe size.)

 

[BUGGAR]

I also agree with you. Be sure to tell the pipers where your bridge points are fixed so they can lay out their fixed and rolling pipe supports accordingly.

 

[MotorCity]

"I prefer not to have a sliding connection on each end."

Don't do that, it is unstable.