New Roof Equipment Platform Stub Column Support

[Eng_Struct]

Hi Group,

I need to design a new steel roof platform on the roof for equipment support. The existing roof framing is OWSJ on gerber girders on wide flange columns. The platform supports will be at the column locations; however, columns do not extend to the underside of the roof. The columns stop below the continuous gerber girder that supports the joist (joist shoe) at the column location.

In cases of a column extending to the underside of the roof, I would typically place the HSS stub with base plate directly on top of the column. However, How do I detail the HSS stub base plate with joist shoe and beam below? Note that each post will have roughly 25 kips of factored load from the post. I will be adding stiffeners in the beam to carry the load down to the column, and will also have to reinforce the columns and footing. I am not sure how to carry the load around the joist shoe.

 

[Eng_Struct]

One thing I forgot to mention is that there are no record drawings for the existing building - the original construction dates back to 1974.

 

[JAE]

I think the idea of creating some type of steel assembly, saddle, straddle, etc. is appropriate in that adding 25 kips onto a little joist seat isn't wise.

Perhaps the assembly could align with the top of the timber deck to give you some more room to span across the joist seat.