Steel Connection Slotted Holes Longer than AISC Long-Slot 1

[MJC6125]

See detail below for a general question I have. In the detail I am trying to brace the top of a new HSS column to the underside of an existing slab on metal deck. I don't want the slab or structure above to apply load to this new column. I am assuming that the floor above and the floor below that the column sits on both may deflect up to 1 1/2" for total live load deflection. So I'd like to have a connection that allows for 1 1/2" of upward and downward movement (3" total). Assuming I'm using a 3/4" diameter bolt, an AISC Long-Slot hole per the AISC manual is only 1 7/8" long. So that would not allow enough deflection. Am I OK to make the slot as long as I need if I'm only trying to transfer bolt shear forces in the perpendicular to slot direction? I see in section J3.10 of the AISC spec (2010) that the bearing strength for long-slotted holes loaded perpendicular to the slot is about 83% as strong as non long-slotted holes. So I assume a longer slot would reduce that even further, but I'm unsure if there's equations you can use to check the further reduced bearing strength? My reactions are low, so I feel like I could be OK.

Does anyone have any further guidance on what is OK and what is not OK for slotted holes that exceed an AISC standard long-slot? Would you do some other type of detail here that allows slip, but doesn't rely on a bolted connection?

 

[WillisV]

Extra long slotted holes will have the same bearing and tear out resistance in the direction perpendicular to the slot as do standard long slotted holes. If you have slots next to one another you would also check the thin strip between for bending as a fixed-fixed beam (this would be the only additional limit State). In your condition with a single slot you are going to be just fine as is.

 

[271828]

One more item: Check bearing on the HSS using the AISC 360-22 Section 3.11b. For the bearing strength, it's pointing to the equation for pins and similar. It probably won't control, but that's the way to check this limit state.

https://www.aisc.org/publications/steel-standards/aisc-360/

 

[STpipe]

I think as long as you're not trying to transfer load in the direction of the slot, you should be ok. As WillisV pointed out, the bearing resistance perpendicular should be the same. Even if you assume an additional reduction, if you're just trying to brace the column laterally, the forces shouldn't get anywhere near the shear/bearing limit state.

 

[MJC6125]

Thank you for the responses. That's good to hear it should have the same strength as a standard long slotted hole. I'll look into the AISC Section 3.11b check when I'm back by my handy dandy steel manual.

 

[sdz]

I expect the column will have lateral loads that will need to be resisted by this connection. Have you considered this?
The connection can be installed initially with the bolt near the upper end if live load movement is down.
You should consider putting a sleeve around the bolt so it can be tightened without clamping the joint.

Ooo eee ooo ah ah ting tang walla walla bing bang
Ooo eee ooo ah ah ting tang walla walla bing bang

 

[MJC6125]

@sdz

I expect the column will have lateral loads that will need to be resisted by this connection. Have you considered this?
Yes, the connection is supposed to resist the lateral loads that the column would see.

@sdz

The connection can be installed initially with the bolt near the upper end if live load movement is down.
This case is on the upper floor of a building, so I expect the floor below the column to deflect just as much as the floor above the column. So equal amount of deflection up and down.

I didn't think about doing the pipe sleeve; I'll look into that. And I was planning on doing a steel angle each side.