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Re: Two way shear in flat slab

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Dear Scott and Bhavin,
 
What Scott has mentioned are all common practice (perhaps) almost all over the world, but all those methods just for increasing shear capacity of the plate, not its ductility. Therefore, all of them will not show a full ductile behaviour when they collapse, but still a sudden or a rather ductile collapse. Different from all of those old fashion methods, Broms' method has made the flat plate become very ductily. Its load-deflection curve is the same as slabs supported by beams or walls. The method use a combination of hanger bent bars running from the bottom plate at some distance from column face, and go to the top of plate and through column and inverted U-stirrups.
Here are some journals that written by Broms:
1. Preventing Progresive Collapse of labs Structures, Journal of Structural Engineering vol 110 no 7, July 1984
2. Punching of Flat Plate - A Question of Concrete Properties in Biaxial Compression and Size Effect, ACI Structural Journal, May-Junae 1990
3. Shear Reinforcement for Defflection Ductility of Flat Plates, ACI Structural Journal, Nov-Dec 1990
4. Elimination of Flat Plate Punching Failure Mode, ACI Structural Journal, Jan-Feb 2000 (I have mentioned it in my previous email)
In those journals, Broms also show some flaws in ACI.
 
Hope this will help.
 
Best Regards
Junata
 
 
 
----- Original Message -----
From: "Scott Maxwell" <smaxwell(--nospam--at)engin.umich.edu>
To: <seaint(--nospam--at)seaint.org>
Sent: Sunday, March 13, 2005 8:51 PM
Subject: Re: Two way shear in flat slab

> Bhavin,
>
> 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.
>
> HTH,
>
> Scott
> 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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