Additional bars not installed around opening in a flat plate

[U4ENIK]

Hi Everybody,
I am working on a project where the slab was poured, but no additional bars were installed around an opening.
Is there a theory that can allow you to take an effective width around/ each side of the opening and say that you can engage more of the adjacent slab bars to make up for the ones that were cut?
For example at columns you can take 1.5xtslab thickness plus the column width in that direction to be used for column effective width.
Thanks

 

[KootK]

I'm afraid not. It sounds as though you've lost the flexural contribution of the disrupted bars. Certainly, the bar tension can be dragged around the sides of the opening. That doesn't change the fact that you've reduced the area of steel crossing the critical section however.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[TehMightyEngineer]

You could always perform a more refined analysis if your initial design was based on a simplified model. Yield line analysis or an FEA analysis might result in lower demand around the opening allowing you to justify the bars available.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

http://www.americanconcrete.com

 

[SteynvW]

What is the size of the opening?

 

[U4ENIK]

All, thank you for your answers.
Kootk,
In your post you mention that you can "certainly" drag the bar tension to adjacent area around the opening. From experience do you have approximate width that you would feel comfortable to engage the slab on either side of the opening. The opening size is 14" wide by 32" long. There are slab bars on each side of the opening, which I can use. The additional bars were not installed only on one side.

SteynvW, see above for size of opening.

Thank you again.

 

[jayrod12]

perhaps a plan sketch showing location of the opening in relation to the support columns would help tailor the answers as well.

 

[KootK]

14" x 32" is not a large upending. Unless it's near a column, it's probably fine by inspection. There really is no limit to the width of opening that I'd be comfortable transferring bar tension around so long as there are bars beside the opening available to absorb that tension and they extend far enough beyond the opening to allow the tension to be transferred via a strut and tie version of a non-contact splice.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.