Composite Beam Anchor Studs Along Deck High Flutes

[cfc]

A steel erector has asked to review a mezzanine project that involves recently installed composite beam framing where the steel anchor studs were installed along the deck's high flute. We have 3" concrete over 1 1/2"x18 ga composite deck (4 1/2" slab) with 3/4"x4" headed studs. In this situation, the deck is parallel to the supporting W12x19 beam.

The deck was installed with the studs installed afterwards. Holes were cut in the high flute to allow stud installation. The erectors then installed duct tape around the high flute stud opening. Concrete is yet to be placed.

Please review ti the attached pictures.

Thanks in advance for anyone's comments or thoughts.

 

[EZBuilding]

Can the high flute be locally cut at this location to allow for the concrete to fully encase the stud?

 

[JAE]

Agree with EZBuilding -
That arrangement shown in the photo doesn't work and wouldn't be acceptable for a composite beam. Not allowed by AISC and would, in my view, negate any composite behavior to a major extent.

 

[JAE]

The decking should be split and opened up to form a concrete haunch down to the top flange of the beam per what EZBuilding says and per AISC Section I3.2c.3 (AISC 360-16)
...and common sense.

 

[hokie66]

Agree that as it is, that beam won't be composite. But parallel to the deck span, what is the purpose of the beam? Does it need to be composite? Does the slab have to bear on the beam for a line load from above?

 

[JAE]

hokie66,
It could be that the beam in question here is a major support girder carrying spaced floor beams - with the floor beams perpendicular to the deck flutes and the main girder parallel to the flutes.

The main girder would most likely want to perform compositely as well.

 

[KootK]

I'm with hokie66 on this one. If possible, I usually try to avoid making my girders composite even if the surrounding infill beam are. That, for a few reasons:

1) to simplify the decking and avoid these kinds of issues.

2) I find that the benefit isn't as great as it is with infill beams.

3) It's my own personal paranoia but I'm made nervous by the curvature discontinuity in the slab at such girders and don't have much confidence in the, potentially very cracked, concrete there to engage the studs well. Some local top steel helps of course.

Sometime designers put studs on top of girders just for the sake of bracing the top flange. For that purpose, I'd be comfortable saying that these studs can still do their jobs.

 

[JAE]

That makes sense, KootK. But we obviously don't know the economics of this particular girder, its span, etc.

The issue to me is - the EOR most likely called for a composite beam and doing what they did here would negate what was on the plans and what the EOR intent was.
That at least would require a question put to the EOR to validate this condition.

 

[KootK]

Oh yeah, if OP is not the EOR and does not know the EOR's intent, this is a must check situation.

The sketches below just show the mechanics underpinning everybody's concern with this when composite action is required.

 

[JLNJ]

I have seen the girders raised up to the top of the deck flute. Seemed like a pretty good solution to me. Obviously it's too late for that here.

Cut the deck out so the concrete can get to the top of the flange. Yes it will require some fussing with sheet metal closures.

Add this to my list of why I don't like composite slabs. This looks like a mish-mash of framing which probably doesn't even want to be composite at all.

Hey KootK - how do you like those studs in the OTHER direction? In the narrow flute? Equally sucky?

 

[Agent666]

Never ever seen that before, usual practice round here is to stop and start the deck either side of a primary beam (girder in american speak), and if required finish off with some flat sheet metal attached to the deck and beam flange to close the gap. Kind of like illustrated below:-

Deck might not even be sitting on the beam flange on one side or both. You have to ask yourself if the beam design relied on full lateral restraint from the deck connections (i.e. designed to the full plastic moment capacity of the beam with no effects of lateral torsional buckling), if it did and the secondary beams were spaced far apart then this arrangement may also impact on the primary beam strength, because deck might span several meters? So instead of beam being restrained at nominally the stud centers, now the effective length could be substantially longer being the length between the secondary beams....

Much easier to do it the way you've shown, so that might be the answer as to why it was done that way....

 

[hokie66]

The beam in question is a W12x19, so by my definition, is not a girder.

 

[r13]

I don't think the beam was designed for full composite action, otherwise there should be more studs, especially near the beam ends. Maybe the work is still in progress. My guess is the studs are there to help stiffen the beam for deflection. Anyway, the communication was broken, as the deck guy didn't lay the deck right, and the stud installer, who should be experienced enough to see the problem, didn't seem to care. Who is in charge of overseeing the construction activities?

 

[cfc]

Thanks to all for the prompt responses. The framing supports a mezzanine space situated above a restaurant. The mezzanine overall area is small; approximately 500 SF. The framing consists of W12x19 beams and girders supported by HSS4x4x5/16 columns. Girder/beam spans vary from 12 ft to 6 ft. The truly scary concern is that the field erector claims the classic "we've done this at other projects" defense. Unknown, if true, if said work was approved by the inspector and/or SEOR or if they just got away with it.

 

[r13]

Take a note and send to the SEOR to review before further progress.