Steel Expansion Connection without Teflon

[JAE]

I've got a set of plans I'm looking at that shows a large steel framed building with expansion joints properly placed across its width. The roof is comprised of steel joists supported by joist girders.

At the expansion joint, the detail shows a joist girder from each side each sharing the same column, with an expanded top plate to accommodate both joist girders.

One of the JG is of course connected to top plate seat with a long slotted hole in the JG seat so that, theoretically, the girder could slip laterally, away or towards the column. However, this is all just sitting on steel - steel to steel - with no teflon plates used to accommodate the slip.

Is this allowed under AISC? I can't find any language about bearing seat-type connections with slip in the spec or manual.

 

[LPPE]

I'm not sure if its allowed, but if you look at the actual thermal force on the connection, I'll bet you'll find it will overcome the friction force no problem!
On the other hand, shouldn't the seat be greased, at least?

 

[SlideRuleEra]

Concur with LPPE on the thermal force. I have worked on rehab of older structures (1930's bridges) where two layers of common 30 lb. roofing felt was originally specified, and used, between the members. Typically was still working after 40+ years. Based on these observations, I have used that roofing felt detail (successfully) on some low cost structures (pipe bridges, etc.)

 

[ChipB]

Typically, these joist girder slotted holes are not accounting for expansion. They are slotted for the same reason base plate bolt holes are over-sized: ease of erection. Once the joist is set, it will be welded to the support steel.

I believe (99%) this bolting requirement prior to welding is one of OSHA's new requirements on joists and joist girders forty feet and over.

 

[JAE]

ChipB- not in my case - it is an expansion joint with a 7" long slotted hole connection in the seat legs of the Joist Girder.