steel beam slide on concrete column options, say 2"+/- slide

[jdengos]

Which option is better:
option 1: put steel base plate on top of concrete column, then add Teflon pad on top of base plate for steel beam to sit on. so beam can slide on teflon pad.
option 2: add steel anchors on steel base plate, slot beam bottom flange, so the beam can slide on top of base plate.

Thanks

 

[BridgeSmith]

The Teflon sheets we do for bridge bearings require a polished stainless steel mating plate. The Teflon is usually fused to the top of a steel reinforced elastomeric bearing pad, with the SS welded to a sole plate. Not sure if it would work without something to take up the rotation and keep the bearing pressure spread evenly across the mating surfaces.

If the friction between the base plate and beam flange is low enough, that will be the simpler way.

 

[jdengos]

@BridgeSmith,

Do you have a detail of it, it sounds like 2 plates. top plate with teflon welded to base plate?
And you pick 2nd option as it's simpler?

Thanks

 

[MotorCity]

These are to vastly different options....one with teflon and one without teflon. Do you need teflon? What are you trying to do?

 

[BridgeSmith]

I'll look for a detail. We haven't done one that needed a sliding surface in a while. Usually, we can accommodate the translation movements by deformation of the elastomeric pad.

We usually bond the PTFE sheet to the top of an elastomeric pad that sits on the concrete bearing seat. The girder will have a steel sole plate welded onto the bottom flange with the mirror-finished stainless steel sheet welded to the sole plate for the PTFE sheet to slide against.

We have some bearings that make use of a 'self-lubricating' bronze plate that the steel slides on, but the those haven't worked well over the long-term, due to the dirt and debris that blows into them. In an indoor application, I would imagine they could work well.

I don't know what issues may arise with just letting the steel slide on steel. I suppose it would depend on how often it moves. The only time we'd use something like that is for energy dissipation during an earthquake, where it would be anticipated to slide maybe once or twice during its service life. I'd imagine steel on steel would produce sounds that are loud and very annoying when they slide, so it this connection is in a building where it would be sliding due to thermal movements or wind loads, I can't imagine that would be acceptable.

 

[BridgeSmith]

A general detail of a PTFE sliding bearing can be found here.

Figure 7 is similar to the style we have used.

 

[jdengos]

Wow, a bit crazy detail for our building. We need to replace one row steel columns at a parking garage with concrete columns. I would like the slab steel framing to slide on concrete column, but I prefer 2nd option since we design the way for indoors, but outdoor garage might use the 1st option instead.

 

[jdengos]

@BridgeSmith
Thanks for help. Since you work on bridges, wondering you know any freebie software that can be used for moving load on spans.

 

[BridgeSmith]

Sorry, no freebies that I know of for bridge analysis.