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PAGAD (Civil/Environmental) (OP)
7 Sep 03 22:48
I'm designing a residential garage floor that will be supported on framing.  I am considering using a steel center beam and wooden I-joists and plywood flooring.

Can anyone tell me what the usual design approach is on garage floors?

a)  What is the usual design live load for a garage with vehicle parking?  This garage will be 50' long by 32' wide.  The plan is to utilize a 50' long steel center beam supported at mid-span and at the ends.  Wood I-joists would span 16' perpendicular to this and be covered with plywood.

b)  Is the design generally based on a uniform live load over the entire surface or are concentrated wheel loads separately analyzed? (hopefully uniform loading).  If concentrated loads, what are the assumptions for the load distribution and what are typical design wheel loads?

c)  While I will of course conduct a structural analysis to determine member sizes and spacing, does anyone have anything to offer on what is typically seen
boo1 (Mechanical)
8 Sep 03 17:03
Garages floors or portions of buildings for the storage of motor vehicles shall be designed for the uniformly distributed live loads of BOCA Table 1606 (50 psf) or the following concentrated load:  (1) for passenger cars accomodating not more than 9 passengers; 2000 pounds acting on an area of 20 square inches; and (2) mechanical parking structures without slab or deck, passenger cars only; 1500 pounds per wheel.

RDK (Civil/Environmental)
8 Sep 03 19:23
I would reconsider the use of a steel beam with wood joists.

Steel beams will loose strength in a fire and may be subject to some serious warping when the firemen put cold water on the hot steel. The beam would have to be fire protected and with the difficulty in placing the heavy steel beam the costs can easily be more than for a wood beam.

I’d re-look at using a wooden main beam.  


Also consider how you will waterproof the floor system. Cars will drip rainwater and in Canada melting snow. This would have to be prevented from soaking into the wood and causing rot.

Rick Kitson MBA P.Eng

Construction Project Management
From conception to completion
www.kitsonengineering.com

PAGAD (Civil/Environmental) (OP)
8 Sep 03 20:38
Thanks.  Good point on the water issue.  Hadn't really thought of that.

As far as the steel beam is concerned, I'm not sure I have any other practical alternative.  The owner wants to span the full 50' with only one center column.  I don't believe that it would be practical for a wood or wood composite beam (if that's what you're thinking) to span this distance under this load.

As far as the 2000 lb concentrated load over a 20 sq. in. area, are you sure that it has to be handled this way?  This is a pretty demanding load on the floor joists and it seems that this would almost always be the governing factor instead of the 50 psf uniform load.  Does this have to be applied to the joists or can it just be that the decking has to be able to handle this load and be capable of spreading it to the joists?

Thanks,
Paul G.

dik (Structural)
9 Sep 03 8:15
Even for residential suspended garages, we generally use a concrete slab, formed using 1-1/2 deck. and supported by a two span continuous beam down the middle (owner has to live with column) or clear span the steel beam (reduced head room).  The concrete can be high strength and sloped to drain for cleaning.  We also provide the owner with a letter (maintenance manual) about cleaning and re-sealing due to salt related problems...
PAGAD (Civil/Environmental) (OP)
9 Sep 03 8:39
I agree that concrete would be better and had discussed this with th owner.  He wants to go with wood as he is looking to construct this himself and feels more capable of doing it in wood.
dik (Structural)
9 Sep 03 9:26
If it has to be wood... then you may want to recommend a good wearing membrane complete with 'grit'... Due to movement, it's likely the only surface that will remain 'water resistant'; it's also pretty pricey and may require a licensed applicator...
boo1 (Mechanical)
9 Sep 03 10:36
Since you did not say where you are located (what code body goverens your area).  These loads are typical for most areas see SBC below:

SBC
Table 1203.1
Mimimum Uniformly Distributed Live Load
garage (passenger only) 50 PSF LL

Table 1203.3
Minimum Concentrated Load
Garages(1) for passenger cars accomodating not more than 9 passengers, 2000 pounds acting on an area of 20 square inches;  (2) mechanical parking structures without slab or deck, passenger cars only; 1500 pounds per wheel: (3) for trucks or buses maximum wheel load on an area of 20 sq in.

I agree with dik concrete w pan is more appropriate.  Discuse with the owner the maintaince, durabilty, life span, and life cycle cost of the two options.
jheidt2543 (Civil/Environmental)
12 Sep 03 10:43
Another thought for garage structural slabs, precast concrete plank.  For most residential applications the precast plank can clearspan the garage, no beams and columns below.  Also, the plank provide a nice clean, flat ceiling in the room below.  With a 1-1/2" - 2" topping slab pitched to drain outside through the garage door, you can solve the drainage problem.  Yes, it is a little more expensive, but it solves many of the problems the first time and it provides a fire barrier too.

Just a thought!
PAGAD (Civil/Environmental) (OP)
13 Sep 03 21:44
Thanks.  This is my first try with this forum.  This is a great asset to have.
EJSP (Mechanical)
5 Jan 04 14:29
Can anyone please relate the 50 psf load rating for garage floor to the 2000 lb/ 2o sq. in. concentrated load?

It would seem the concentrated load rating would always be significantly higher, by magnitudes, then the requirement for a 50 psf load rating?
boo1 (Mechanical)
5 Jan 04 15:50
The concentrated loading is a tire foot print area:

20 sqin x 100 psi(max truck tire pressure)

The 50 psf is a live load over the entire area

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