ACI Guide to Shear Reinforcement in Flatslabs 1

[FinnB]

I am working on a number of projects at the moment with very heavily loaded flatslabs which support up to 5 stories of blockwork building.These slabs are generally in excess of 600mm deep and are designed by F.E.M. Line loads from the buildings blockwork walls are taken directly onto the slab.

Bending in the slabs is reasonably easy to cater for,but shear around column heads is more limiting. I have quite a lot of experience in flatslab construction and am very aware of how they must be designed.

I use mainly British Standards which limit the allowable shear capacity of the slab to 2 x applied load, no matter how much reinforcement is placed in the slab.

My question (eventually!!!) is I have heard ACI codes specify using a steel section in the shape of a cross.

1)Is this true
2)Can it be made up from standard steel sections(as opposed to being a proprietary system).
3)How much can the shear stress in the slab be increased in relation to the applied load.
4)What code do I need to refer to and is it downloadable on the net.

Thanks

 

[HochwaltPE]

1) Yes. It is called a "shear head" and is covered in Section 11.12.4 of ACI 318-02.
2) Yes.
3) Shear strength on the reinforced section is limited to 7 root f'c.
4) Looking at the ACI website (

http://www.concrete.org),

I do not believe that it is available for download.