Composite construction for exterior use

[WWTEng]

I am considering using a composite floor+wf beam system for a mechanical room . The roof for this area is nothing more than a trellis, so the floor itself is exposed to weather. Floor construction is 2" metal deck with 4.5" normal weight concrete (6.5" total) over WF composite steel beams.

I am thinking of adding an additional 1" of concrete as an extra cover (ignore in my calc). But would that be enough, would I need to do something additional with the concrete mix or should there be any sort of treatment over the finished floor? The area is going to be closed for the most part and is not supposed to be salted but I suspect that the maintenance guys would eventually have to go up there and would need to salt the floor occasionally.

 

[MiketheEngineer]

Structurally if it works - you shyould be OK. BUT seal it to keep salt out!!

 

[WWTEng]

Mike, thanks.

I forgot to mention that this is in the midwest, so snow will accumulate.

 

[msquared48]

Why would you add so much exta weight to the roof rather than a steel platform with steel grating which is much lighter?

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[spats]

What about the need to waterproof the floor? Also, if it's dead flat, it won't drain properly... think rain, not snow. I'm not sure why you want to add extra concrete. What does that accomplish?

 

[WWTEng]

Spat, M2: Here is the update, there is going to be a built up "roof" over the composite slab to address most of the concerns that you mentioned.

As to why it needs to concrete, because there is a mechanical room below which needs to be covered, can't do that with steel framing and grating. Also, rest of the construction is composite so the idea is to keep everything similar.

 

[JAE]

Using metal deck/concrete slabs in an exterior situation can create problems - especially if the deck is a composite deck essential to the strength of the slab (i.e. the deck serves as the reinforcement for the slab system).

The concerns are the influence of water seepage into the concrete resulting in long term deterioration of the deck - whether there is salt or not.

In your last post you suggest that there will be a roof over this deck so as long as water cannot get to the concrete there should be no concern over rusting of the deck.

There are some publications out there dealing with the use of metal deck/concrete for parking garages. I can't recall who published these but a high level galvanized finish and vented deck seems to be what I recall being recommended.

 

[SteveGregory]

How about a cast-in-place slab that is shored instead of the metal deck?