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Composite beams
2

Composite beams

Composite beams

(OP)
I am working on my first major project with composite beams. I am designing the structure as unshored. But I have some questions in my mind and I am hoping to get some input on this forum. For example,

1) What is the approximate cost of placing studs over the beam?
2) My understanding is that 3/4" is the only recommended size for use as stud per AISC 350. Is that correct?
3) I understand that the studs should project a min of 2" above the deck rib and that there should be at least 2" concrete cover over the stud. Correct?

RE: Composite beams

1) I imagine the answer to this question will depend on where you are.  I use a value of $2.00-$3.00/stud installed

2) I have always used 3/4" dia studs and I don't see why you couldn't use smaller.  I do not have ASIC 350 in front of me so I can't really comment.

3) According to the AISC studs are required to be placed 1-1/2" above the deck and 1/2" below the top of slab.  This basically correlates to every composite deck catalog I have seen that requires 2" of cover above the flutes.

RE: Composite beams

Ref AISC 360-05 specifications:
2) stud shear connectors 3/4" or less  in diameter. You could also use channels.
3) After installation studs shall extend not less than 1 1/2" above the top of the steel deck and there shall be at least 1/2"  of concrete cover above the top of the installed studs.

RE: Composite beams

(OP)
Thanks for the input. The 1/2" clear cover over the stud is something I wasn't clear on. I thought it was supposed to be 2".

RE: Composite beams

(OP)
Another question: Is it more practical to have uniform stud layout rather then freeform, and how common is it to use non-uniform layout?

RE: Composite beams

Freeform?

Usually the studs are spaced evenly.  The only time I have seen them not spaced evenly is in regards to girders where you will have different stud counts between the locations of the point loads.... ie a girder with point loads at the 1/3 points may have an (18) (5) (18) pattern.  Even the studs are spaced evenly between the point loads.

RE: Composite beams

(OP)
Steel, thanks. By freeform, I meant non-uniform layout. And yes my question was in regards to a girder where I have two point loads at 3rd points, and I was wondering if I could use a stud arrangement of say 18, 4, 18.

And now I have another question. I understand that the recommended minimum composite action is 50% (base on some articles I read online). But I have some beams where the composite action is around 30-40%. what are some of the problems I could expect with a low composite action such as this.

 

RE: Composite beams

No offense, but all of this stuff is answered in the AISC Specification and Commentary for Chapter I as well as the associated design examples, all of which are available on AISC's website for free...

RE: Composite beams

As Willis suggests, all of this information can be found in the manual.  Either in the specific chapter or the commentary.

With regards to the % composite action.  AISC used to require a minimum 25% composite action (I believe) but they have removed that requirement for the 13th edition.  I don't know about the 14th edition as I do not own one.  I thought the commentary specifically addressed the removal of this limit and why they went in this direction.
 

RE: Composite beams

(OP)
Willi, Steel. Thanks.

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