Composite beams 2

[WWTEng]

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?

 

[SteelPE]

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.

 

[DST148]

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.

 

[WWTEng]

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".

 

[WWTEng]

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

 

[SteelPE]

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.

 

[WWTEng]

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.

 

[WillisV]

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...

 

[SteelPE]

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.

 

[WWTEng]

Willi, Steel. Thanks.