big opening in the concrete slab 1

[Stormin74]

In our design of concrete building, The concrete slab is designed as 9" thickness. The contractor misreaded the design drawing and put a 10' by 1' big opening 5' away from one of the column. Next column is 24' away from four sides of this column. This opening was originally designed as 1' by 1' mechanich duct. Now the floor concrete has been poured with all the rebars stop at this opening. Can anyone come up with a good solution of this?

 

[JAE]

Tear it out....

or....provide supplemental steel beams underneath to create a proper load path to the columns.

 

[MarcbSE]

Agree with JAE,
Either tear it out and replace it per the plans or provide new supplemental support structure below the slab.

 

[csd72]

A couple of web links to get you thinking:

http://www.concrete.org/General/CI2807mota.pdf

http://www.allbusiness.com/manufacturing/chemical-manufacturing-chemical-product/4074555-1.html

It appears tp me that the issue is only in one direction as the other direction is only missing the 1' width.

You need to check if the other spans are still sufficient taking into account the lack of moment continuity across this opening. If they are still okay then a steel beam either side of the opening may be sufficient (fire rated of course).

csd

 

[apsix]

Prop slab to take dead load.
Remove concrete around opening, leaving rebar intact.
Splice in new rebar over opening, with full length splices.
Pour concrete.
Remove props after 3 - 4 weeks.

 

[WpgKarl]

apsix - I was thinking the same thing as you. I once had the joy of fixing up a structural slab that the plumbing contractor thought was a slab on grade (luckily it was only over void form!).....So he merrily went along and cut out trenches for the plumbing (it was for a dental office) and he cut so many bars, it was unbelievable!

We ended up having them expose the rebar and they added couplers, but it was very congested and it become a 3 dimensional issue, as some bars had to be cut further to make it all fit c/w couplers.

That always bothered me, the contractor screws it up and then the EOR has to come up with a fix for it.

 

[nicam]

Did you do a FEA in your original design? if so just modify your design with the new opening so you can see whats happening with the forces redistribution.

btw what kind of contractor would make such a gross error and why did'nt any one notice before the concrete was poured??

 

[lkjh345]

As others have mentioned, check the existing slab as is.

If your columns are 24' o.c. each way, did you design the slab as a two way slab? There is a lot of redundency (sp?) in a two way slab system.

Hopefully, with the opening 5' away from the column, punching shear shouldn't be a big problem. (Assuming this is a flat plate slab).

If the slab does not work as is, Apsix's solution is quite reasonable.

Might substitute couplers for full tension splices (See Lenton Lock Rebar Splice System) as this would reduce amount of demo required.

JMHO.

 

[hokie66]

If your contractor made an "error" like this, how confident can you be in anything else he has done? Did he put in the reinforcing, or only half of it? Does no one inspect floors before they are poured where you are?

 

[msquared48]

I agree with apsix, but would limit the amount of concrete to remove and try to field weld the reinforcement. Tension Lap splices can be quite long.

Mike McCann
McCann Engineering

 

[ron9876]

I agree about splicing in new reinf. Welding may be a problem if not weldable reinf.

 

[msquared48]

If it is 40, no prob. If 60, then preheat. Should be one or the other. No worries.

Mike McCann
McCann Engineering