Frame garage floor 3

[COEngineeer]

When I design frame garage floor I usually use 1.5 DL (4" of concrete + framing = 1.5x65psf). I also use 2 scenario of LL, 40 psf or 3000 psf point load. I use 1 1/8 plywood. I usually design it for 600/L live load or 240/L total load (with the factored DL). My question is, according to IBC, I can only put 4" of concrete. If I have 23' x 23' of garage and the architect wants a drain in the middle, how do I slope the concrete? Is lowering the grade 1" in the middle enough? Can I put more than 4" so I can slope it 1/4"/ft and still have thick enough concrete in the middle? How thick is not thick enough for framed slab? I appreciate your feedback.

 

[dik]

I would use a greater slope... 1" is less than 1% and I try to use 2% for garage floors to help ensure sufficient drainage without having 'puddles'. Are you sure you can't design for a greater amount of concrete? else, you may have to alter the framing to give deflection, ie. use 2x12 and taper top to give 2" slope or something like that or slope the joists.

Dik

 

[COEngineeer]

Dik, I am using 1 3/4x11 7/8 LVL @ 16" O.C. Dik, usually I slope the joist but this project the architect wants a drain in the middle. According to IBC, if I support the slab with wood framing, I cant have more than 4" of concrete. Any thoughts?

 

[IceNine]

Can you run a beam line down the middle at a lower elevation, and slope the joists down from each side?

 

[twinnell]

Run two beams, one on each side of the drain.

Would it help to switch to light gauge framing?

 

[COEngineeer]

I want to stay away from metal decking twinnell. IceNine, Thats possible. I think I have decided to just tell them to put 5" of concrete and slope down to 3" at the drain. So that is about 1.5% slope. I know it is more than 5" but I figured it is 4" nominal if you average the thickness.

 

[dik]

Can you slope the top of the beam towards the drain? That is, cut away the top sloping from each end until it drops a couple of at the middle, then flush frame the floor joists that frame into the beam. This can give you a slope in two directions. The 4" concrete topping would then take on a hyperbolic parabaloid surface.

Dik

 

[COEngineeer]

I have 1 steel beam simply supported in the middle. I guess I can rip the nailer a little. I like that idea dik. Ill ask the contractor what he wants to do. I have a feeling he will want to put 5" of concrete to 3" instead and hopefully the inspector won't notice/mind.

 

[rday]

Leave sloping the surface to the finisher. They do it all the time.

My thought would be to ditch the wood framing altogether and do a structural slab. You could use the steel beam to support it as well. I think twinnell was suggesting cold rolled framing, not steel pans, to get away from the wood issue.

I just don't think a wooden garage floor with a concrete topping is a good idea.

 

[COEngineeer]

rday, it is a pretty common practice here. we design with very low live load deflection and also 1.5 DL to take care of the long term creep.

 

[DonPhillips]

Try reading some of the often overlooked provisions in Chapter 1 of IBC. It grants the Building Official the ability to accept designs following standard engineering practices. If you design the structure to support the loads, using NDS, and you seal your design, this overrides the prescriptive provisions of the IBC.


Don Phillips

http://worthingtonengineering.com