existing columns extension

[Heldbaum]

Hello everybody,
I've been working on that project where we are adding 2 additional floors to the existing 9story steel bldg. All external columns on the last two floors (8th and 9th) are double angles 6x4x1/2. I would like to extend all the existing columns ale the way up and connect them together with beams and use the heavy studs for walls and c joists for floor beams. How would you do that, I mean I think it would be easy to use the same cross section for new columns (easy to splice) but on the other hand I can't imagine beams-column moment connections..? How should I do that, should I weld a cap plate at the top of the exist. DL and use HSS or W beam..? Thank you in advance !

 

[JedClampett]

I'd weld a plate to the top of the angles. Just make sure they're regular old weldable carbon steel. They could be some kind of old cast iron or ductile iron sections. Then convert to a section where you can more easily make your connections.