studrail orientation in slabs

[ajk1]

Are studrails that are used to increase slab punching shear capacity around supporting rectangular columns, best placed radially or orthogonally around the column? It seems to me that I read an ACI paper a number of years ago that said they were most effective when placed radially. It may even have said that they would not achieve the calculated strength if placed orthogonally, but my memory is not good. Does anyone recall that ACI paper? Any comments?

I ask this as part of my general review of our office typical details and not in relation to any specific job.

 

[Celt83]

Check out ACI 421.1R

Open Source Structural Applications:

https://github.com/buddyd16/Structural-Engineering

 

[cliff234]

ACI 318 also has typical illustrations showing studrail placement around square and rectangular columns.

 

[KootK]

1) I do believe that performance has been shown to be better with a radial placement. I also believe that this is more common in European codes an practice.

2) I think that a rectilinear stud rail placement is more construction friendly and, as such, you might struggle to sell Canadian contractors on a radial scheme.

 

[MotorCity]

Does placing them radially imply that you will need more stud rails than if they were placed orthogonally?

Spaced radially = orthogonal spacing + additional rails at say 45 degrees?

or

Spaced radially = orthogonal spacing rotated at, say 45 degrees?

 

[ajk1]

thanks cliff234. I will check out ACI 318. Thanks Celt83 - I will also try to check ACI 421, if we have it in the office.

Thanks Kootk for your advice to stay with the rectangular layout of studrails. I have learned to respect your advice, which has proven sound in our past correspondence on this site, so that is what I will do.

 

[KootK]

Does placing them radially imply that you will need more stud rails than if they were placed orthogonally?

I believe that it's the same number of stud rails. Just an efficiency thing.

This will be pretty abstruse but the model in my head for this as a truss of which the column top steel is the tension chord. In this respect, I actually prefer the orthogonal layout because, with the radial layout, I feel as though the truss chords and webs are in different places. That said:

1) I'll not argue with the results of testing.

2) There are three dimensional effects in play that my brain surely isn't smart enough to fully grasp.

 

[rowingengineer]

The testing results for stud rails have been somewhat disappointing. To get the stud rails to fail in punching shear, some tests have been carried out with large amounts of top steel in the slab. To get the performance similar you would need to detail similar amounts of top steel. There was some good articles published all over the place about stud rails in 2011 when this was highlighted by independent testing. Recommend a quick google search to understand the issues. As kk rightly points out above, there is a truss formation above the columns making the amounts of top steel important in shear design.

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."