Rebar Detailing for Slab Opening 1

[chocomocha]

Hi! I would like to know in what ACI is the Standard Rebar Arrangement around Slab Opening found? I placed 2 diameter 10 trimmer bars around openings, I just want to be sure if I am right. I can't find it in ACI Detailing 2004 :-(

Many thanks again.

 

[sdz]

Is that a suspended slab or a slab on ground?
Can you add a sketch?

 

[csd72]

Normally you would provide an equivalent are to those cut by the hole as a minimum.

what is the size of the hole and where?

 

[rscassar]

The December edition of Concrete Internation by the ACI had an article titles "Bar Detailing at Wall Openings". Regarding corner bars which I believe is what you are referring to the article states:

"Corner bars are opening bars placed on a diagonal at each corner. Although they aren’t explicitly required, it’s good practice to use them—they provide more efficient restraint of the likely cracks at the re-entrant corners."

 

[chocomocha]

Openings are for suspended slabs and walls... 150mm thickness for suspended slab and 80mm for walls. I have read several articles online, and each gave diffent multipliers for the length of the rebars from the edge of
the opening.

 

[msquared48]

For the ??? dimensions, extend them a minimum of 40 bar diameters beyond the edge of the opening.

Also, there is ons set of bars that just dies at another transverse opening - the larger one. Since those bars cannot be extended toe 40 bar length, you need to either hook the bars or use a 90 degree bend for each bar.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[ATSE]

Blanket recommendations about openings in elevated slabs is not rational without discussing the opening location relative to column strips and columns, and whether beams are used or not. For a flat slab deck with 7meter x 7meter bay spacing between column grids, a 0.8m diameter opening in the center of intersection middle strips is easy. A 0.4m diameter opening right next to a column can be problematic.

Regarding lap, the bigger the opening, the longer the replacement bars need to be (but not necessarily the trim bars). Sometimes it makes more sense to run replacement bars the full length of the span (over beam or wall supports below). The replacement bars (bars to make up for being interrupted) must eventually transfer tension to the interrupted bars, or carry the full loads of the bay without trying to transfer tension to the "original" bars. Sometimes this is more than 40 bar diameters, depending on the separation distance between interrupted bars and replacement bars.

Rules of thumb are dangerous here, but at a minimum, much safer to go with 2 x standard lap splice length. Better to define strong bands in your slab to transfer shears and moments, and develop those bars as needed.

 

[csd72]

There are a few articles on this available on line:

http://www.cement.org/buildings/tech_note_floor_openings.pdf

http://books.google.co.uk/books?id=...ng around openings in suspended slabs&f=false