Concrete Metal Deck attached to Side of WF Beam

[8thStreet]

Hi All,

I am working on a large custom residence where the floor system is concrete metal deck system with all steel framing. The architect wants to reduce the depth of the floor system, so instead of the deck running continuous over the top of the beams, they want the the concrete metal deck to be inset into the depth of the wide flange beam, so that top of concrete is flush with top of the wide flange.

Please see attached sketch.

Do you forsee any issues with this type of system?

I know that all of the deck spans will be single span, so that reduces the effectiveness of the floor system. Also, with all of the decks designed as simple spans, so they will likely be some sort of cracking in the finish located above the steel beam.

Thanks.

 

[structSU10]

I don't see an issue with this type of system beyond some of your concerns.

Any reason a different structural system is not used? deep long span deck, CLT, hollowcore? to stick with steel beams, even the delta beam system or similar may make some sense.

 

[azcats]

Are the beams shored during construction? Top detail removes top flange restraint during concrete pour.

 

[phamENG]

You also have to be careful about diaphragm detailing. Could be interesting at the boundaries.

 

[slickdeals]

The first detail will make it very difficult (maybe impossible) for the installer to install the deck. You will need to look at how close the deck is to the underside of the flange and how much bearing you have.
Have you investigated into girder slab or deltabeams? If it's a custom home, I am sure the owner has some money to spend

 

[phamENG]

That deltabeam stuff is pretty neat. Anyone have any idea how the cost compares to typical frame and deck with concrete?

 

[structSU10]

We had the deltabeam guys in the office recently. It is definitely pricier - they say that it become more economical with 4+ floors due to height saving on the building (facade costs and such use to 'pay' for the premium on the framing).

 

[KootK]

1) My pitch below. For a number of reasons, including slick's sage constructability concern, this screams HSS to me.

2) Rebar dowels optional. I think that it would be great to have them but fully acknowledge that this kind of voodoo tends to raise the hackles of residential contractors.

3) Delta beams are neat and have their place. However, I replace them regularly with precast beams because:

a) Lead times push eight weeks where I work.

b) The economy isn't there for small quantities.

The detail below effectively is a DIY delta beam anyhow.

 

[YuleMsee]

Moving away from the detailing question, can you achieve any depth saving in using a composite deck vs this?

 

[8thStreet]

Thanks everyone for the advice. I thought this system would work out well - I just wanted to make sure that I wasn't missing something. Appreciate the thought about bracing the top flange and constructability.

We will stick with the WF because because we have a lot of cantilevers. Thanks for the creative detail Kootk - I will try to sell that one on a different proejct.

 

[KootK]

So which detail are you going with?

We will stick with the WF because because we have a lot of cantilevers.

How do you see cantilevers factoring into the decision? I'd have thought that an HSS would be better for that as well (lower LTB bracing requirements).

 

[slickdeals]

@KootK:
Are you relying on fire proofing the HSS? I don't think your detail as such will get the fire rating. I am not pushing the deltabeam system, but I know they don't need any fireproofing even with an exposed bottom flange.

 

[KootK]

Are you relying on fire proofing the HSS?

Yesir. Do you contend that, with fireproofing, this doesn't work? I've done something similar on may occasions with HSS / WF side supporting hollow core. Granted, that has topping running over top.

 

[Ron]

Suggest control joints at the WF to control cracking. They will occur.

 

[r13]

I personally prefer the second option, which is less problematic that the first.

 

[jayrod12]

If forced to do a wide flange beam, because personally I'm more prone to the HSS solution, I'd be using a L5x3LLH to avoid to fastening issues noted above. I think detail 2 is quite convoluted for diaphragm load path. And more fabrication.

 

[r13]

The only addition to detail 2 is a few pairs of vertical stiffeners to bring the force into the web, and the bottom flange. The stiffeners can reduce strength demand in the Z channel, and enhance the wide flange in torsion.

The reasons I don't like the first detail are: 1) it introduce moment to the wide flange (suggested by the thru web reinforcing steel), which can have considerable torsional effect at unbalanced load conditions; 2) the potential air pockets below the flanges, which are very difficult to avoid, and detect.

 

[HouseBoy]

Curious if you have considered "conventional" composite beam and slab construction.
(You know, welded studs on the top flange.)
I used it for a garage addition recently where depth was a concern.
Don't know how the need for cantilevers will affect that layout though.

KootK - Are the "rebar couplers" you indicate a specific product or is that just a term for the fact that you would be welding rebar to the side of the HSS? SEEMS like that weld design will be tough to develop the bar capacity (but maybe I just am not familiar with that detail).

 

[skeletron]

Second option over the first. I sat through a lecture where the speaker talked about using the first detail (angles welded to the web of the W beam) after pressure from an architect. It was an absolute headache getting that deck in place and plumb, not to mention the load path is less than ideal.

 

[KootK]

My main beef with detail #2 is that unbalanced load will produce torsion in the beam and, since the beam isn't integrated into the slab torsionally, it'll be on it's own for resisting that. I don't consider this a big deal though, just something to be designed for.

KootK - Are the "rebar couplers" you indicate a specific product or is that just a term for the fact that you would be welding rebar to the side of the HSS? SEEMS like that weld design will be tough to develop the bar capacity (but maybe I just am not familiar with that detail).

Weldable rebar couplers are a commonly available product. The couplers and their welds can easily be made to develop small diameter bars. Whether or not the HSS walls could handle the full strength of the bars without yielding is another story but, for me, not an important one. My intent with the bars was really just to lock the beam into the slab torsionally and, more importantly, gain some composite action stiffness between the beam and the slab.