Waffle slab parking deck with overhang

[leighcheri]

I've been asked to calculate the allowable load on the overhang portion of a waffle slab parking deck. How do I treat this case? The L/s for the overhang section is < 2 so it normally would be treated as a one-way slab but the joists make it so it deflects as a two-slab.

Thank you in advance. I hope I've explained my problem clearly.

 

[leighcheri]

Correction to my original post: L/S > 2 (30'/9')

 

[cap4000]

I have done this calculation before but can't find a book that directly indicates its OK to do so for a cantilever. Here goes. Based on your dome data, void volume and top slab thickness their is an "average equivalent slab thickness". You have to compare both the transformed sections and equate each of the moments of inertia. You must get the 1980 or 2002 CRSI Manuals to review their calculations procedures and adjust it to your overhang condition. Hope this points you in the right direction. Good Luck.

 

[hormozzadeh]

I think the joists are not rigid enough to act as supports.so the slab doesnt treet as a one-way slab.so you shoud distribute the loads based on the stiffness of slab and joists.I can suggest you using SAFE or ETABS2000.

 

[rapt]

leighcheri,

If by overhang you mean cantilever, the L/s > 2 rule would not apply anyway. This is for normal spans supported on 4 sides.

With a 9' cantilever and a 30' span, it will be 2way.

Do not forget to calculate real deflections if you are using safe or etabs or any other FEM package, allowing for cracking and long term effects.