External reinforcement concrete

[MaartenD]

Hello World! (to quote the output of what might be the most popular computer program ever written)

In a residential building I have a half slab floor which cantilevers 1m over a masonry wall. I prescribed some additional reinforcement on the top net of the floor above the wall because I needed this to resist the moment created by the cantilever. However the contractor didn't place the additional reinforcement and casted the concrete before I could come to check. On photos, I saw afterwards, I saw the additional reinforcement wasn't placed. The architects are very reluctant about placing an extra column so my idea was to place external reinforcement. Do you have any experience with this ? I especially doubt on how to connect the external reinforcement with the concrete. I think it's better not to use more bolts than nessecary in order to prevent destruction of the top net. My preference would be to use steel reinforcement as I am afraid the conctractor doesn't have any experience with composite reinforcement.

I hope my explanation is clear.
Thank you in advance for your help.

Best regards,
Maarten

 

[ANE91]

We’ve had success with NSM. Few can install it properly. Best to take out any DL deflections and engage the NSM by propping the cantilever before install. Note that it’s not external. External PT doesn’t make sense here. You could also get creative and suspend the cantilevered end off rods, but the architect would probably hate that, too.

I’ve linked you a European site, since you used meters: https://www.concrete.org.uk/fingertips-nuggets.asp?cmd=display&id=457

 

[KootK]

I think it's better not to use more bolts than nessecary in order to prevent destruction of the top net.

Are we talking about steel plate bolted to the slab? I'm surprised that would be architecturally palatable, especially on the back span into the interior.

In a residential building I have a half slab floor which cantilevers 1m over a masonry wall.

I question whether or not this is a good solution for a short cantilever considering:

1) The bolted connections will exhibit some slip prior to engagement. If adhesive isn't used in conjunction with the bolts, the external reinforcement may not do much to limit unsightly top side cracking.

2) You won't be able to hook the reinforcement as you would rebar and, with bolts, you may be developing your bars quite slowly. Be careful that you can actually develop the bars to a useful degree over that short, 3' cantilever length.

 

[HTURKAK]

I prescribed some additional reinforcement on the top net of the floor above the wall because I needed this to resist the moment created by the cantilever.

Although the situation is clear , if you provide the reinforcement details of additional top steel and existing top steel you may get better responds.
I would consider first chipping the cover and weld additional reinforcement to the existing top rebars (if any) then repair the grooves with epoxy grout .