Concrete Flat Plate slab Replacement connect to existing columns 1

[autokoz]

Removing the flat plate slab of three lower floors in an existing 24 story building due to sever corrosion of the top and bottom reinforcing steel. Removal will reach 50% of each floor area.

Any information for reinforcing steel detail to re-establish slab and column connection (intending to keep the slab concrete within the column)

 

[civilperson]

Welded rebar is very effective in rehab vs splice or mechanical connectors. Needs good technique, (preheat and correct electrode).

 

[JAE]

autokoz,
Could you introduce steel jacket plates around the concrete columns, bolted into the sides of the columns, to create support...along with a perimeter notch cut into the lower column just under the slab? ... see attached sketch.

Just an idea. You'd have to verify that the brackets and the notch all have the capacity to support the vertical shear.

Otherwise, extending structural steel channels up the sides from floor to floor can also work - allowing more distance for more anchor bolts. The channels could serve as long vertical brackets - with a seat plate on the top to support the shear.

 

[csd72]

Nice detail JAE!

A few extra notes, you would need to specify shoring for the column when you notch it, and also temporary horizontal braces at each level to prevent the column buckling over 2 floor levels.

 

[JAE]

Yes, the detail would require a good deal more evaluation - worry about the anchor bolts clearing column rebar, shoring(as you suggest), and checking the shear on those notches, etc.

 

[OzEng80]

Don't forget to check punching shear around the column as this can govern flat plate thickness. JAE's 'thickening' around the column is a great way to account for this.

 

[hokie66]

Why did the slab steel corrode? Is there also a corrosion problem with the columns? Bracing the columns while the floors are replaced will be critical. That's a lot of load from the 20 some floors above.