Suspended concrete slab

[Timothy Hampton]

Hi all,
I'm designing an earth bermed house and need to calculate the dead load weight limit on a suspended concrete flat slab. The clear span width will be 20'. Short of hiring an engineer at this point of the project, does anyone have a formula to figure out the thickness and reinforcement requirements to support a certain load? I'm currently working on calculating the psf of the soil that will be placed on top of the roof slab. Thanks, Timothy

[Rich]

I could get the calculations out of a book - but it's too lengthy for me to type. And I only understand about half of it. :)
Would be much better off to have an engineer look at it - so they can take into account any drift loads and that type of thing.

Also - could you provide the correct email address in your profile so I don't get an email everytime someone responds to your posts - thanks.

[Timothy Hampton]

Sorry about the email address Rich, I figured it would probably be some long complicated calculation to find out the amount of weight say, a 4" slab with #4 rebar would hold! I've built a couple of flat span bridges but then they were engineered for us. I was hoping to get a rough idea just for estimating purposes at this stage of the game. Thanks,Timothy

[Rich]

4" with #4 isn't going to span very far by itself. I would imagine there would have to be some post tensioned cabled if only 4" deep. I honestly doubt it would hold itself up if spanning 20'.

[Timothy Hampton]

Rich you're right, I don't think a 4" slab would hold up much. I have seen a concrete roof done using hollow core precast panels with a 2" topping slab. I was wondering if that would be a more cost effective method. If I had to pour an 8 or 10" slab, that would take something like 100 yrds to do 3600 sf. A precast method would certainly save from doing all the false work and forming too.

[Rich]

Hollow core panels would be a great way to go. Just make sure the embed plates are right before ordering them :)