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Suspended Concrete Garage Floor
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Re: Suspended Concrete Garage Floor By  maniac

Posts: 0

1/3/2007 5:16:00 AM

"suspended Concrete Garage floors" ?


   

Re: Suspended Concrete Garage Floor By  Uncle Bob

Posts: 0

1/3/2007 5:23:00 AM

I think he means above ground; as over the basement or on a hill side and above grade.


   

Re: Suspended Concrete Garage Floor By  maniac

Posts: 0

1/3/2007 5:37:00 AM

Pre-stressed or post-tensioned?
Common but needs engineering.

R403.1 General. All exterior walls shall be supported on continuous solid or fully grouted masonry or concrete footings, wood foundations, or [b]other approved structural systems which shall be of sufficient design [/b]to accommodate all loads according to Section R301 and to transmit the resulting loads to the soil within the limitations as determined from the character of the soil. Footings shall be supported on undisturbed natural soils or engineered fill.

Who approved the structural system?
AHJ, can require engineering....


   

Re: Suspended Concrete Garage Floor By  Building Inspector 8

Posts: 0

1/3/2007 6:07:00 AM

No i mean they are suspended where the actual garage floor is open underneath for storage. For instance if you have a house with a full basement and a two car garage at grade. The space that is below the garage which is normally unexcavated is used for storage and has a concrete floor just like the basement and accesses the basement, not the house itself.


   

Re: Suspended Concrete Garage Floor By  maniac

Posts: 0

1/3/2007 6:19:00 AM

What is the floor [b]suspended[/b] from or to?

Or is suspended the word you wanted?

How thick is the slab?
Where are and what is the bearing points for the slab?
What is the reinforcing?


   

Re: Suspended Concrete Garage Floor By  Building Inspector 8

Posts: 0

1/3/2007 6:44:00 AM

Hello and happy new year maniac.
#1 & #3 In response to your questions. the outside edges land on the exterior concrete foundation wall that loads to a spread footing that is 8" thick x 16" wide that bears on undisturbed virgin soil having an appropriate bearing capacity. Most of the time there will be a steel beam in the center of these suspended floors that have support columns that land on reinforced pads that bear on appropriate bearing capacity virgin soil also.
#2 The slabs are always 6" thick.
#4 The reinforcing is #4 rebar usually spaced at 12" o.c. Maximum placement of the rebar over the steal beams is usually on 6" centers perpindicular to the steal beam or beams.
#5 The house plans are usually drawn by a design professional and sometimes an architect.


   

Re: Suspended Concrete Garage Floor By  permitguy

Posts: 0

1/3/2007 7:14:00 AM

BCG,

We see a fair number of these as well. As there are no prescriptive requirements, they must be engineered. R301.1.3.


   

Re: Suspended Concrete Garage Floor By  maniac

Posts: 0

1/3/2007 7:33:00 AM

I agree with permitguy
Must be engineered.


   

Re: Suspended Concrete Garage Floor By  Building Inspector 8

Posts: 0

1/3/2007 7:42:00 AM

Thanks again for the responses, allways a pleasure gettin other professional opinion.


   

Re: Suspended Concrete Garage Floor By  constructionarbitrator

Posts: 0

1/3/2007 8:15:00 AM

BCG:

Do the floor joists under the concrete floor remain to support the floor, and are they sized to carry the dead and live loads, or is the concrete slab spanning from foundation to steel beam to foundations wall, the joists being only form-work which is removed?


   

Re: Suspended Concrete Garage Floor By  Building Inspector 8

Posts: 0

1/3/2007 8:20:00 AM

The later of the two scenarios, constructionarbitrator


   

Re: Suspended Concrete Garage Floor By  constructionarbitrator

Posts: 0

1/3/2007 9:31:00 AM

You''ve got a structural slab and definitely need engineering. Believe it or not, when I was a young apprentice carpenter we routinely built structural slabs as you describe, but I can''t imagine it now. I can remember wondering what was going to hold it up when the journeymen sent me underneath to do the dirty work of removing the form-work. When I asked the journeymen what held the floor up, they said they didn''t know, they had always done it that way, sound familiar?


   

Re: Suspended Concrete Garage Floor By  Building Inspector 8

Posts: 0

1/3/2007 9:57:00 AM

Yea exactly. once the form work is removed the only thing left is the steal beam and that''s it.


   

Re: Suspended Concrete Garage Floor By  FredK

Posts: 0

1/3/2007 10:33:00 AM

You need this R301.1.3 Engineered design. and in the IBC under table 1607.1 is a load table you can use.
17. Garages (passenger vehicles only)40 PSF Note a

a. Floors in garages or portions of buildings used for the storage of motor vehicles shall be designed for the uniformly distributed live loads of Table 1607.1 or the following concentrated loads: (1) for garages restricted to vehicles accommodating not more than nine passengers, 3,000 pounds acting on an area of 4.5 inches by 4.5 inches; (2) for mechanical parking structures without slab or deck which are used for storing passenger vehicles only, 2,250 pounds per wheel.


   

Re: Suspended Concrete Garage Floor By  Darren E

Posts: 0

1/3/2007 10:48:00 AM

BCG -

I agree: P.E. Design and SEAL required.

Very recently, I came across a structural garage slab almost identical to what you described above. The contractor did the right thing and called for a pre-pour inspection. When I ask for the design document (btw - not submitted at plan review - just decided at the last minute to make the floor structural) - the contractor said that this was the standard way to do garage floors - I''ve done 3 or 4 just like it - so I don''t need a design.

Long story short: the PE called for almost 3X the steel, with very detailed edge requirements.

Don''t think the contractor will go that route again.

DRE


   

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