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RE: Composite Floor conventions

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All I have seen is for the total number of studs for the span to be indicated unless an unequal distribution is used due to loading variations.
Ram outputs the total number for the beam (this is not stated explicitly but implied in the beam module manual in the composite beam section section-8.6.4)
The commentary in the ram manual also mentions that the 25% was required in the ASD code, then moved to the commentary in the 2nd ed LRFD.  It is noted in the 13th ed in the commentary as a practical limit but not required (page 16.1-311)
I generally try to avoid getting the studs closer than 1' on beam sections if possible, but allow it on girders. I have not come across anything specific that prohibits or requires the 1' spacing, though I do tend to apply it when placing studs on short infill sections.  SDI does require that the deck be "fastened" at an average spacing of 12" but no more than 18" apart so it may be worthwhile to avoid mixing in puddle welds.

Michelle Motchos, PE
Stevens & Wilkinson of South Carolina, Inc.
Columbia, Sc 


  




-----Original Message-----
From: Jordan Truesdell, PE [mailto:seaint1(--nospam--at)truesdellengineering.com] 
Sent: Tuesday, August 08, 2006 11:28 AM
To: seaint(--nospam--at)seaint.org
Subject: Composite Floor conventions

It's been years since I've done a composite floor by hand - back when a 3/4" stud was comfortably assumed to carry 21kips. I'm knee deep in a retrofit, and have managed to lose track of where things should go, and where all the specifications are. Too many years relying on computers, I suppose. Anyway...

On composite floor system drawings, it's common to label the beams with end reactions and number of studs, which are equally spaced along the length of the beam. This is the way RamSteel outputs the data, and it flows right onto the drawings.  I cannot remember whether the call out - which is normally labeled as "number of equally spaced studs" - refers to the number of studs on each half of the beam, or on the entire beam. 
Is there a consensus, and what is it (yes, I have a question in to RAM as well, but that's from the software side).

It has come up because I have a retrofit job, and the beam in question would probably calc in the normal load case with the 10 studs indicated. 
Since its 28' long, 10 studs would meet the criteria for 36" o/c max spacing.  It does not, however, meet the 25% composite "rule". Which brings me to the next question: where is the 25% limitation written in the AISC spec, or is it a guideline which is not written. I have gone through the spec (13th Ed) and commentary and can't find it. I understand the inherent problems with low-composite action beams, but I'm looking for a specific limitation if it exists.

Last question...after rereading my course notes in advanced steel design, I have several indications that the studs should "never be less than 12" o/c".  And, now, almost a decade later, I can't remember if the call out is for never placing studs closer than 12" (requiring double rows), or never to have fewer studs on a beam than would be in place if put on 12" centers.  I have a feeling it is the latter, but don't have a definitive answer.  Does anyone else use the 12" rule?


--
Jordan


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