Help-Garage Slab

[jjeng2]

Ive done this calculation many times before in my old job but Im on my own now and dont have any reference calcs. Im doing something really stupid wrong but I cant figure it out. I have a large garage in a house with a basement under it. The max. span between filler beams is 9'. Im using 18Ga, 2" Lok Floor Composite Deck with a 5.5 inch slab. Im using 60psf live and 60psf dead. My unshored construction spans are ok. My uniform loads are ok. I applied a concentrated load of 2000lb to the center of the span and my moment is huge. It is 4 times the uniform load moment per foot width. No slab will work with this, so Im forgetting something. Also, as I read IBC it seems to say you can design either for 50psf uniform load OR 2000lb concentrated load. I would think this means, whichever is greater but it does not read this way. Help..I need to get this done ASAP.

 

[jjeng2]

I think I figured it out. I found an example in the deck design book. But if anyone has any comments, let me know...

 

[broekie]

How much tributary slab width are you assuming resists the 2000 pound point load?

 

[jjeng2]

Broekie,
Thats what I thought the problem was but I couldnt get the numbers squared away in my head. After going through the example, I think it will be fine. The example was almost the exact same conditions.

 

[fepc]

jjeng2
I read the IBC the same way. You may use either one. I assume you have more than one span so use continuity and reinforce the slab over the support. Other wise you will get cracks in the slab. The other choice is to use the steel deck as a form and use reinforcing in top and bottom of the slab. See the CRSI handbook for one way slabs.
Regards,
fepc

 

[LPPE]

The USD catalog has an concentrated load example problem on page 19.

 

[jjeng2]

Thanks LPPE, thats the one I found.

 

[DKPE]

I, too, am designing a suspended garage slab for a residential home. Did anyone come up with an answer for the 2000 lb vs. 50 psf code scenario? As I read 2000 IBC, section 1607.4 states that you should compare the 2000 lb point load with the 50 psf uniform load and use the one that produces the greater load effect. As stated in the above thread, the 2000 lb point load always produces a much higher maximum moment on a simply supported structure. When the 2000 lb point load is used, the slab design seems terribly impractical from the suspended garage floors I have seen in the field for this application.