Base connection between existing concrete column and cantilever steel girder

[h-badawy]

Dear experts

I have an issue in the site, the client wants to upgrade a steel shed for gas station to a modern one. The structural system of the existing shed now is space truss rested on concrete columns (6m height)spacing between four columns are 10m x10m , the new one will be simple girder (after demolish the space truss only) with cantilever in all sides. My problem actually in the connection between the girder and the existing concrete columns in the same place of the fixed (splice

)connection of the cantilever.please give me ur suggestions about any proposal of the connection shape in this zone .
Attached is a sketch of the layout and section of the shed connection.

Thank you

 

[JoshPlumSE]

What are the anchors into the existing column? What does the existing column reinforcing look like in this location or do you not know? Obviously, you can get into situations where your post-installed anchors can't be done because you encounter existing bars when you drill the holes.

Your sketch makes the columns look round. What's the diameter? I'm concerned about the existing bars, but also wondering about edge spacing and confinement.


FWIW, I think your connection idea has merit. It's not as stiff as a welded connection, but I don't see why it wouldn't work conceptually. What's the cantilever length compared to the 10m back span?

 

[phamENG]

It looks like you just drew a bolted beam to beam moment connection and then drew a column under it...right?

In order of preference;

1) If the existing bolts are serviceable and can align with workable gauge of the beam(s) you're proposing, do that but switch to a field welded condition. Bolt the two full length beams down to the existing columns, then weld the flanges and webs.

2) If the existing bolts are serviceable and cannot align with workable gauge of the beam(s) you're proposing, add a short HSS stub column with a thick base plate that can use the existing anchors and then design a bolted (or welded) connection at the top of the steel stub column (doesn't need to be tall...only as tall as it takes to get erection clearances in there).

3) If the existing bolts are NOT serviceable, then chip away the top 12-24in of the column, remove the old bolts, and recast the top of the column with bolts designed for your condition. I don't think post installed anchors of any sort will cut it for this.

 

[h-badawy]

JoshPlum and pham
Actually i have the as-built drawings and I don’t have any problems with safety of the concrete columns and footings . In any case the arch. Needs to raise the height of the shed for 1.5m more ,so i will cut the existing anchors and chip 1 m from top of the concrete columns to make a dowels for new short pedestal and place the new anchor bolts .
The issue here in the connection of the bottom flange of 2.4m cantilever with back span girder especially the site weld will be very difficult and how i will put the base plate and the anchor bolts with the high strength bolts of the bottom splice connection?????

Thank you

 

[phamENG]

Well if you have to raise it 1.5m anyway, I'd go with my option 2 above...combine it with chipping and setting new anchors as needed. Why will the site weld be difficult? The only things I can think of are 1) no welders in your area or 2) no welding inspectors. Otherwise, it's not a particularly complex procedure. I've seen welding done at heights multiple times. It can be done safely and with relative ease by competent welders with the right equipment.

 

[h-badawy]

You mean the bottom flange of all the cantilever and back span girder with the perpendicular girder will be welded with base plate ?

Thank you

 

[phamENG]

No. I mean raise it that 1.5m by using a steel stub column with a moment connection to the concrete column below (thick base plate). That will allow you the clearance below to steel framing to make your connection.

 

[KootK]

 

[h-badawy]

Thank you all for your useful ideas, and appreciated your support.

Thank you