economy of composite beams (steel beam with concrete over metal deck)

[Gopher13]

I understand one big advantage of composite beams (steel beam with concrete over metal deck) is reduced floor to floor height resulting in savings of finishes and MEP.

I have a case where they will be building a mechanical mezzanine inside an existing building. I am framing this mezzanine with steel wide flange beams, metal deck, and concrete topping. I don't really have any constraints that limit the depth I can use for structure. Anyone have a feel for how much weight in steel beam needs to be saved to offset the cost of field welding studs to the beams? I designed one of the main girders by hand and found a savings of about 10 pounds per foot when working compositely with the concrete. However, that same beam would require 3/4 inch diameter studs every 6 inches or so.

 

[jayrod12]

The welding of the studs usually isn't super expensive since it's done by a stud gun generally.

I'd bet this would be highly location dependent. If you've got a steel supplier that you're friendly with, might be worth a call.

What about shop installing the studs and making the steel deck simple span between beams?

 

[KootK]

The advice that I've gotten from steel fabricators in Ontario and Alberta is that it takes about 1000 studs before the mobilization and demobilization costs of welding the studs on site make economic sense. I feel like a lot of beams wind up having an about 14 studs each end.

 

[Gopher13]

Minnesota is pretty much Canada I think it is comparable..........1000 studs at +/- 28 studs per beam is 37 beams. My mezzanine is 20 ft. x 70 ft. so that will be way more beams than I will have. I appreciate your insight. Thanks KootK!

 

[jayrod12]

Minnesota is pretty much Canada I think it is comparable

Oddly enough, up here we say the exact same thing.

 

[BridgeSmith]

For bridge girders, studs welded in the shop we estimate at about $1 per stud. For welding in the field, doing enough studs for an entire bridge (typically 1000-2000 studs), we estimate around $10 per stud. While it's true the stud gun is the same, the welder needed to supply 1100 amps needed to operate the stud gun for 3/4" studs (1400 amps for 7/8" studs) is a big, heavy and expensive piece of equipment, and the generator needed to supply the electricity to the welder is a bigger beast.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[dik]

I've heard the 'break even' number is about 500 headed studs... but don't honestly know.

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-Dik