steel column splice with girder on top cap plate 2

[irizarry]

I'm trying to design a column splice over an existing 8" diameter steel tube column. The problem is that the top of the column supports the end of a joist sit on a cap plate above the existing column. Normally Id splice new column with old by end plates, but since the girder is connected by cap plate, I'm not really sure what to do?

 

[jike]

There are 2 approaches:

1)Column discontinuous
2) Column continuous

1) Check out to see what needs to be done to transfer the column load thru the girder. For instance, stiffeners or other elements. Make sure you maintain stability of all components.

2) Another approach is to allow column to be continuous by creating brackets to support the girders and joists. This will create eccentricities that will cause bending moments in the column for various unbalanced load conditions. Column should be checked and reinforced or upsized to accomodate this.

Good Luck!

 

[irizarry]

Thanks Jike,
The connection has to be discontinuous, since the connection between the girder and the lower column already exists, and it would be very difficult to change it. The problem is that the girder is a built up truss girder and I really dont see how to add stiffeners in order maintain load continuity and stability from new upper column to lower one. If someone knows of some guide or have seen this done, Id appreciate advice.
Here I posted a very elemental drawing of the actual connection where I want to do the column splice.

 

[apsix]

What's the width of the top chord bearing relative to existing column?
What size is the new column relative to the existing column?

A few more drawings/photos would help a lot.

 

[hokie66]

I think you could just cut a slot out of the new column to fit over the joist end, weld the new column to the cap plate, then provide some fitted splice plates all around.

 

[apsix]

I was thinking that you could cut the top chord back to allow the new column to sit on the cap plate, and then weld the chord onto the new column.

 

[BAretired]

Either of those ideas works, but hokie's is the easiest if the width of joist permits.

BA