Studrails...how much can they increase punching shear capacity

[asixth]

How common are studrails and how much can they increase the punching shear capacity of a flat slab? Are people regularly including studrails when designing flat slabs?

I have a 9" (225mm) flat slab on 16" (400mm) square columns. I have calculated the punching shear capacity at 122kips (500kN) while the punching shear is 210kips (950kN). So can providing studrails essentially double the punching shear capacity of a flat slab. There is no guidance provided in the code I am using with respect to punching shear so I will be designing using the findings of a research paper by Lim and Rangan titled "Studies on Concrete Slabs with Stud Shear Reinforcement in the Vicinity of Edge and Corner Columns".

What would be the best document to use when designing studrails to increase the punching shear capacity of a flat slab?

 

[apsix]

asixth

Both Reid and Ancon market stud rails in Australia.

Ancon design program can be found here;

http://www.anconbp.com.au/products/punching-shear-reinforcement/design-program/

 

[asixth]

apsix

Thanks.

Do you know whether punching shear reinforcement is common in flat plate construction. I know provided a thickening around the column (drop panel) has added benefits such as reducing deflections, decreasing flexural reinforcement over supports as well as increasing the punching shear capacity, but if these products are so effective, why aren't they used more often in construction?

 

[rowingengineer]

Asixth,
The selection of drop panels v's studs V's shear ties is very dependent on size/complexity of slabs and timing of the project. The studs have a lag time due to shipping (also means extra $$), and our local contractors are unfamiliar with the product, thus this always causes problems on site. Mind you the dowels are the worst, normally you buy a huge amount and i can tell you, that it is more than likely that they will forget two, stuffing up your last pour for at least a few days.

Punching shear reo ties is common in PT slabs, however band beam type construction is the preferred method for PT. From a point of view of local practices (brissy) drop panels would be the common selection. However this doesn't mean you should rule out your flat slab construction with studs option, just need to talk with the contractors and his form-worker to work out the $$.


Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it

 

[rapt]

Asixth,

For relatively square column grids, flat slabs with drop panels (proper ones dimensioned to L/6 each side of each column) provide the most economical solution, but the client/architect has to be willing to have the non-flat soffit. For rectangular column grids, band beam solutions are the most economical but again you have the non-flat soffit problem.

Personally, I hate punching shear reinforcemnent in relatively thin slabs from both a theoretical point of view and also from the construction aspect, so, if thickenings are allowed, I would always go that route. The other option is column captials (that probably makes me sound old!).

Some codes limit the amount that can be taken by punching reinforcement, eg BS8110 limits the total shear to 2 * Vc so you would just make it on this basis.

 

[oneintheeye]

I believe most suppiers have their own design software or design office to assist. Some are probably accreedited to appropriate standards (whatever they are in your conutry) such as BRE in UK. Probably not comman due to acceptance problems with clients/checking engineers, unknown to contractor and accreditation/insurance issues. We had a seminar on them from one supplier and they seemed very quick and easy to install.

 

[frv]

My advanced concrete professor mentioned that stud rails are a very effective method of increasing punching shear capacity.
The main reason there are no provisions in the code (specifically, ACI 318) that deal with stud rails directly is that these are proprietary systems and the companies still hold patents on their designs. Once the patents expire, stud rails will be addressed directly.

 

[ishvaaag]

Even so, they are to be considered inferior to closed stirrups, because not fully embracing chunks of concrete.