Vulcraft composite VL deck vs shear studs 1

[kodstruct]

Hello,

I have successfully used Vulcraft 2VL & 2VLI composite decks over steel joists for floor framing systems over the past 10years. One of my colleagues is saying it's better to use shear studs on steel beams instead. Personally, I feel like it will be expensive to weld the studs for two to three story buildings. Can we just use Vulcraft VL composite deck on steel beams provided that we specify the puddle welds? I've always felt like using the composite deck (VL or VLI) with specific puddle welds is enough for partial composite action after checking the requirements.

Note, my floors are always 5.5" total thickness.

Thanks.

 

[SteelPE]

You use composite deck with no shear studs and develope partial composite action between the steel beams and concrete slab? What % of fully composite action do you develope and what code are you using?

 

[kodstruct]

Less than 10%. Steel beams depth is not an issue. My colleague came from a firm where they often do high rise buildings so I understand the benefit of using full composite floor systems. Our local contractors (being working in the area for 10 years) will certainly "screw up" by placing studs in wrong places etc.. so I usually use Vulcraft VL deck (composite with the concrete) on steel beams/joists for easy installation.

 

[hokie66]

Composite deck and composite beams are different things entirely.

 

[steellion]

I am unaware of any code provision that allows composite action to be considered with puddle welds as the only shear transfer mechanism. The welds get the shear into the deck, what gets it into the concrete? Friction?

Don't be afraid of shear studs. I can only speak to the areas I've worked, but composite steel construction is THE preferred and most common method for steel buildings. You need a detail that explains how the shear studs should be laid out, and then it is something the contractor should be able to easily handle.

Are you saying that you use concrete on steel deck supported by open-web steel joists as your default floor framing system? I acknowledge that there are certain applications a system like that makes sense, but that would be unusual to use all the time.

 

[kodstruct]

Thank you all.
I have designed composite floor system in the past (some 15 years ago in Houston-Austin area) before I joined this small local firm (in a small city in Wyoming). The contractors here always ask us to find alternatives to our design to fit their knowledge, which is fine with me because the construction cost is reasonable. I was telling my new colleague that I don't see any difference in using composite deck on steel joists vs. on steel beams provided that I am not designing composite floor systems.
Also, our firm work on buildings between 2 to 3-story.

 

[Archie264]

Yes, certainly you can use composite deck without using shear studs; just don't design the beam for any composite action! In that scenario it is simply a regular steel beam and the concrete acts separately, even though it's on a a composite deck. See what Hokie66 said.

What makes the Vulcraft deck "composite" is that it has interacting lugs that allow it to engage the concrete so that the deck and concrete act together. But getting the beam and concrete to act together requires shear studs.

 

[XR250]

I wonder what the savings actually are using shear studs when you consider the cost of the design, studs, stud welding and increased difficulty installing the metal deck. I guess it depends on the spans and size of the building. I personally have never used them because most of my buildings are small enough not to justify it.

 

[Archie264]

Excel, there can be considerable material savings, enough so, apparently, to make up for the additional labor, judging by the system's widespread acceptance in many places. (I'm very bad at cost estimating so that's really my only basis for saying that.) But attaching the studs doesn't take that much effort as they simply "shoot" them onto the beam with an electric welding gun.

One thing to be aware of, though, with steel-concrete composite systems is that they can be particularly susceptible to vibration. I think that's a function of how thin the slab can be made to be. It's something to watch out for.

 

[msquared48]

Excel:

The savings comes in that the beam supports the wet mud and a construction load of about 20 psf, preferably unshored, but the presence of the studs supports the additional live load with no more steel.

Mike McCann
MMC Engineering

 

[XR250]

I agree it likely makes sense on a large building but may not on small building. It is design, fabrication and installation labor costs that typically trump material costs. Don't they have to do on-site testing of random shear studs? Another cost that can be more easily spread out over a large building. Also, I wonder how much additional the metal deck installer is charging to burn holes for the studs?

 

[Archie264]

The studs can actually be shot right through the metal deck. I'm not advocating for or against the system, by the way; I'm just discussing it.

 

[msquared48]

Excel:

You said "to burn holes for the studs"... Really a non-issue here...

In that the studs are always welded to the steel beams at the bottom of the flutes in the deck, and the stud gun welds through the deck to the steel beam below, no cutting of the deck is needed. It is an automatic process.

Mike McCann
MMC Engineering

 

[steellion]

The rule of thumb I use is that the material/labor cost of each shear stud is roughly equal to 10 pounds of steel. If studs result is a reduction of the beam size, they're usually worth it. I find that serviceability concerns usually control the design over strength for the composite systems I design. In our office, it is rare to NOT use composite beams. The concrete is there already, why not use it for the structure? It's just dead weight otherwise.

 

[JoshPlumSE]

I have only cursory knowledge of the vulcraft composite joists and how they achieve shear transfer. But, there were a couple of other systems (Hambro and Vescom) that relied on a deformed top chord or such. It seemed to me a reasonable way to ensure good shear transfer.

I'm not sure that any of these systems has gotten all that much traction in the industry. So, my guess is that there must be SOME reason for that. Maybe they don't offer great cost savings, maybe they don't perform as well as promised, or maybe they're just a pain to work with (for either the engineer or the contractor).

Personally, I'm keeping my eye out on these systems as they would seem to be quite promising. I just would like to get more feedback (positive or negative) from more engineers that are using them.

 

[XR250]

Interesting, I did not know thru were installed thru the deck.
@Steelion, so you are saying if the studs are 12" O.C. you are saving 10 PLF in beam weight?

 

[steellion]

Excel, no, what I meant was as a rough order of magnitude cost estimate to determine if composite construction will be the most economical system for your floor, compare non-composite steel weight to composite (steel weight + 10 pounds/stud X quantity of studs). The cost of one installed stud is roughly equivalent to the cost of 10 pounds of installed steel beam.

Example: 30 foot span:

Non-composite: W18x35 required. Weight = 35PLF X 30 FT = 1050#
Composite: W16x26 with 14 studs required. Equivalent Weight = 26PLF X 30 FT + 14 STUDS X 10 LB/STUD = 920#.

 

[kodstruct]

Thank you all with your comments.
The building I am talking is 3-story office building, each floor has about 6,000 sq.ft. Since the contractors that always work on our projects have never seen us designed composite floor systems, I think i would rather use the composite deck on steel beams. With this I can still get the 1H fire rated the architect requires.

Thanks.

 

[WillisV]

Agree w Steeellion - backup info that also includes this number:

http://www.modernsteel.com/Uploads/Issues/April_2000/0004_02_economy.pdf

 

[dhengr]

Kodstruct:
I agree with Steellion’s approach too. If the conc. is already there, why not use it to your advantage, assuming it is cost effective. Why not talk to a couple of your local contractor friends and see what they would think of the idea of shooting studs from above, and through the deck? Bring them some of the appropriate stud welding literature, and explain the potential advantages. What do they think their costs and difficulties would be, could you save enough steel, in the beams to make up for their extra costs? And, of course, your extra fee and extra effort should be included in that cost and serviceability study. There isn’t anything wrong with stretching the capabilities of your contractors, particularly when you make them part of that process. Just don’t spring it on them, if they’ve never done it before. That would just fulfill your negative prophecy.