SFRM vs Membrane Horizontal Assembly

[admiralArchArch]

What considerations (cost, ease of construction, future maintenance, penetrations, etc) do you make when choosing between a UL fire-rated horizontal assembly that is either a floor-ceiling assembly or a directly applied protection method? For instance construction type 1A protected steel podium construction (3HR), group R-2 with some amenity spaces.

 

[Jay Smith]

In podium construction the decision is made before we start. I’ve done several podium projects and have reviewed dozens for QC purposes and have never been asked to look at any other podium solution besides cast-in-place concrete.

 

[admiralArchArch]

We have a fairly small podium, so we are not doing CIP or precast as we vetted with structural and the GC. So metal deck+steel beams.

 

[steveray]

Do you actually "need" the podium?

 

[admiralArchArch]

Do you actually "need" the podium?

Yes, were are doing 5 stories of IIIA over 1A. Using horizontal building separation allowance per 2018 510.2.

This isn't really a code question, more of a best method, pros vs cons, etc, question. We rule out CIP/post tension etc already.

 

[steveray]

Yes, were are doing 5 stories of IIIA over 1A. Using horizontal building separation allowance per 2018 510.2.

This isn't really a code question, more of a best method, pros vs cons, etc, question. We rule out CIP/post tension etc already.

I get it...but you were talking cost so getting rid of a separation is certainly a saving....Grade up around the garage?

 

[Paul Sweet]

Applied fireproofing would have to have excellent impact resistance for a parking garage. Columns would probably need steel plate covers.

 

[admiralArchArch]

Thanks, but no parking garage. I guess I'll explain the building. We have 6 stories total. The site slopes substantially so on the low elevation is our 1A, at the high side it's basically slab on grade at that point and that is floor 2. Floors 2-6 are IIIB (sorry I said IIIA earlier). III over A is needed because we need 6 floors to meet the developers unit count.

Here is a bad diagram explaining. I'm just curious what the practical and technical considerations are if we spray the steel structure with SFRM or use a floor-ceiling assembly. We will have HSS columns below the podium, and columns along the exterior will probably need to be hidden in the exterior wall.

 

[Jay Smith]

Assemblies like UL D739 look reasonable for 3-hour. Not extremely thick on the concrete. Spray it all with fireproofing. UL D916 makes sense, too. Thicker concrete. Unprotected deck. But I’d wonder about wasting height. Bar joists would allow you to thread ductwork and sprinkler pipe through the structure. So if you can work out the penetrations, I’d probably look pretty hard at something like UL G529 or G512.

As an aside, I’ve been involved with a project similar to this. We stacked up 6 levels of Type IIIA. City of Atlanta accepted the lowest (partial) level as a basement. Google photo attached. Grade behind this curved face is a courtyard at the 2nd level.

 

[khsmith55]

Thanks, but no parking garage. I guess I'll explain the building. We have 6 stories total. The site slopes substantially so on the low elevation is our 1A, at the high side it's basically slab on grade at that point and that is floor 2. Floors 2-6 are IIIB (sorry I said IIIA earlier). III over A is needed because we need 6 floors to meet the developers unit count.

Here is a bad diagram explaining. I'm just curious what the practical and technical considerations are if we spray the steel structure with SFRM or use a floor-ceiling assembly. We will have HSS columns below the podium, and columns along the exterior will probably need to be hidden in the exterior wall.

Did a similar project 2 years ago, except the first story was parking. With the guidance of the Contractor and working closely with the SE, ended up doing a 2 story CIP concrete Podium with 4 stories of V-A on top . The advantages we found were; basically one trade for the Podium super structurer and all the V-A loads could transfer out "anywhere" because the minimum slab thickness was of sufficient strength to carry the loads. Just some thoughts for you.