Metal Deck without Concrete for floor

[NFExp]

All

I am working on a high end restaurant and it has a 3rd floor roof deck of a pretty decent size. Currently the roof is designed with steel I beams and a concrete filled metal deck. Above the concrete will be a water proof system and with pedestal pavers.

The architect asked us to remove the concrete and just use the metal deck for support. The metal deck would have ridged insulation and the pedestal pavers would bear on top of the ridged insulation.

The roof deck will be serve as large gathering space. I can get the loads to work but my concerns are vibration and noise from the metal deck. Based on how the roof deck will be used, I cant get past not using concrete....

The architect is adamant about no concrete....

I would like to hear if anyone has had a similar design...

 

[SwinnyGG]

Metal deck w/o concrete is going to be LOUD. Assuming the architect is directing you to use the same W deck you would've used with concrete, I'm not even sure the decking is designed for that use case. I'd be looking to go to metal grating with water control underneath, or some other solution. W deck with no concrete in it is a weird solution.

 

[KootK]

I don't love it for the vibration / noise thing but might be willing to let it slide if your client has been warned on that front and is adamant.

 

[TRAK.Structural]

Going to have to re-space your beams to make the un-topped metal deck work, and obviously if you were using composite beams in the previous design than that has to be changed as well. The system you are describing is essentially a roof that's designed for higher dead and live loads; I've done that many times with type B metal deck so structurally it's feasible.

 

[phamENG]

Absolutely feasible, and while vibration could be an issue, it can be designed for. Not too worried about noise as the insulation and roof protection boards will help with that. It's not like you'll have a bunch of jack boots directly on 20ga steel.

Now, no matter how much you design for vibration it will be worse than if there was concrete, and it will probably make a bit more noise...so I'm with KootK. Make sure you inform them that they are insisting on an inferior product. One that technically meets the minimum standard, but is less than what you would put in if you had your druthers.

 

[driftLimiter]

I've done these floors with a a metal deck as the diaphragm and load carrying decking. On top they used a 1" layer of something called resin-deck.
This was for a storage facility though, I don't know how the floor will respond to foot fall vibrations.

 

[NFExp]

Thanks for all your replies. It sounds like we are mostly in agreement with the vibration issue.. I think I'm gonna stick to my guns on this one and keep the concrete. Its a high end water front restaurant that should get a ton of visitors. I'm not pushing the envelope on this issue.

 

[271828]

I only have experience with one such floor and it had pretty severe vibration problems and needed an expensive retrofit. I designed the retrofit and it wasn't easy.

By all means, check it for vibrations. You can adapt the methods in the AISC Design Guide 11 for this purpose.

Two things you can quickly check:

The total psf of the floor shouldn't be small. If it's 25-30 psf, that's not a good sign.

Compute the natural frequency using the Design Guide 11 equations at the first of Chapter 3. If it's below 8-9 Hz, that's not a good sign.

 

[KootK]

I'm not pushing the envelope on this issue.

Hey, sometimes the best service you can offer your client is technical leadership. You are a trusted "consultant" after all, not a pandering lap dog.

So it becomes an exercise in persuasion:

1) Wear a corduroy sportscoat over your best, Steve Jobs black turtleneck.

2) Use emotionally evocative architectural terms like "rickety" and "institutional". Vacillate between inducing fear and passing out verbal hot toddys.

Kidding... I'm sure that you're probably better at this than I am. You do you.

 

[phamENG]

Vacillate

Has anyone ever used this word on the forum before? Well done, KootK...well done.

 

[lexpatrie]

Found 11 usages, back to 2006, on December sixth. And Koot used it last year. I'm not going to say anybody is using it correctly. It doesn't mean alternating. It is waffling between two options unable to decide, i.e indecision.

Is a verbal hot toddy a compliment or an alcoholic drink intended to impair judgement?

 

[phamENG]

indecision

That's how I read KootK's post. It's often how I feel in those situations. I don't really know how I'll respond until the first words come out of my mouth. Once I'm committed, I'm committed, though. But plenty of vacillation before hand...

 

[KootK]

I'm not going to say anybody is using it correctly. It doesn't mean alternating. It is waffling between two options unable to decide, i.e indecision.

From the Latin root vacillare, to sway.

As in to sway the emotional state of one's audience between two extremes:

1) Warm and fuzzy security = institutional structural performance = verbal hot toddy.

2) Fear and uncertainty = rickety.

Induce a state of emotional turmoil and then, BAM!!... bend the room to your will.

At least that's how I meant it. I work while I Eng-Tip, and sometimes Eng-Tip on my phone. Ergo lots of butt ugly BB sketches and little concern for vocab & grammar. If I've done anything more than be understood, I've overshot and wasted time that could have been better spent on other things.

 

[dold]

If I've done anything more than be understood, I've overshot and wasted time that could have been better spent on other things.

Seems like a good email signature. Particularly for responding to waves of front-end RFIs from detailers.