Composite Deck on Non-Composite Steel Beams or Joists

[FootNMouth]

In our market composite steel beams with concrete on composite metal deck is a common framing system, however it's cost increases dramatically on smaller projects (footprint less than ~10,000 SF) due to many reasons with one being the cost of renting the Nelson stud guns to install the shear studs. For this reason, a popular system on these smaller projects is steel joists with concrete on non-composite form deck. Typically the joists are spaced at either 2' or 4' on-center.

Question: Are there reasons why using composite metal deck on either non-composite steel beams or non-composite open-web steel joists should be avoided?

The advantage of using composite deck in lieu of non-composite is much large live loads can be obtained and/or greater spacing of the framing members can be achieved.

Possible Floor Systems Described Below

1. Composite steel beams w. composite steel floor deck (e.g. 2VLI)
2. Steel open-web joists w. non-composite (form) deck
3. Non-composite steel beams w. composite steel floor deck.
4. Non-composite steel beam w. non-composite (form) deck.

 

[BridgeSmith]

For bridge construction, studs on the girders only is the typical construction method. The older specs limited the effective concrete flange was limited to 12 times the concrete deck thickness. That limitation has been removed in the newer (LRFD) design spec, so we now can consider the effective flange for each girder to be equal to the girder spacing. Basically, the entire deck is effective, even with 9.75' girder spacing and an 8" deck.

 

[dik]

I've often used composite steel deck on regular steel framing; am I understanding the question? I've also designed steel framing to act compositely with the deck over.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[structSU10]

I have done that as well - I generally avoid bar joists floor systems so for small jobs will do composite deck on wide flanges with no studs.

 

[FootNMouth]

@dik thanks that did answer the question. Just wanted to make sure as I do not see it often from other firms.

 

[BridgeSmith]

composite deck on wide flanges with no studs.

How do you provide the composite action without studs? Or did I misunderstand your response?

 

[GeorgeTheCivilEngineer]

Yep, Use of composite deck on non-composite beams, or even onto blockwork walls, is quite common here.

Even with a composite beam system there will usually be a few shorter spans that don't need the composite action even if there are studs.

Only thing to be aware of of you leave out the studs is whether you need studs to provide tying action or restraint.

 

[BridgeSmith]

Use of composite deck on non-composite beams, or even onto blockwork walls, is quite common here.

Are you talking about a composite deck, where the concrete is composite with the steel form pans, but not the joists/beams?

 

[dik]

It's common practice in these environs. Only for large projects are the floor beams composite, generally... sometimes to reduce deflections you can use less than flexural minimum shear connectors.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[GeorgeTheCivilEngineer]

Are you talking about a composite deck, where the concrete is composite with the steel form pans, but not the joists/beams?

Yes

 

[KootK]

Are there reasons why using composite metal deck on either non-composite steel beams or non-composite open-web steel joists should be avoided?

Not that I know of. I do this all the time. A local rule of thumb here is that, if a project would involve fewer than 1000 studs, it's not economical to absorb the mobilization and demobilization costs of having the studs installed.

According to AISC's design guide, non-composite beams still benefit from a fair bit of composite action without the studs which is handy for vibration.

If you're going to detail a hard working diaphragm, it can be nice to have studs for deck shear transfer. That said, welds and PAF fasteners can get that job done just fine much of the time.

 

[dik]

I recall literature from 'way back' (about 50 years) about studies done with composite construction that the deck puddle welds are effective up to about 40% of the design loading. Studs greatly help with deflection issues (and vibration).

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik