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Re: Two way shear in flat slab

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Typical construction in the US for flat plate (two-way slabs without
perimeter beams) relies on the concrete alone for handling shear (i.e.
punching shear).  Thus, the typical way to deal with such issues is to
increase the thickness of the concrete slab overall, add a drop panel
(i.e. locally increase the concrete thickness) and/or add a column
capital.  It can be any combination of the three.  That is the typical (or
even "preferred" way) from my experience.

If that is not enough or other factors prevent such actions (i.e.
archtectural requirements), then you can do things like stud rails (metal
headed studs welded onto a flat plate that is in a cross like
pattern...the "legs" of the cross extent into the slab on four sides of
the column [assuming an interior column] with the "center" of the cross
in the columns...note that I believe that this system is propreitary,
which is why it is not directly showing up in the ACI 318 code); shear
lugs (basically steel WF shapes again in a cross pattern that go through
the joint...I believe ACI 318 does discuss this option), or even
"standard" stirrup reinforcing (can be tough if the slab is relatively
thin).  I would at least take a look at ACI 318 first to see what it has,
then you can look at ACI 421.1R-99 (Shear Reinforcement for Slabs).  I
have not seen the final version of ACI 421.1R so I can say how helpful (or
good) it is, but it should at least give you some place to start.


Adrian, MI

On Sat, 12 Mar 2005, Bhavin Shah wrote:

> Dear all,
> Sub : Two way shear in flat slab
> We are designing two way flat slab ( without capitals ). In this regards kindly note the following :
> 1) It is a G+4 building having approximately area of 700 m^2 at each floor.
> 2) Max. span of slab is 10.0m.
> 3) Capitals are not provided as per the architectural requirements.
> 4) Computer model is generated (using STAAD) having frame elements. Slabs at each level are also modelled with the help of plate elements.
> 5) Analysis is completed for vertical and lateral loads.
> Your input will be appriciated for following points regarding design of slab :
> 1) Shear stresses will be generated in both the direction at the junction of slab and column. Kindly comment on the reinforcement details required for the same.
> 2) Additional details required for the punching shear.
> Regards,
> Bhavin Shah

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