Circular Slab

[sb79]

Hello

I am designing a pedestal with a circular slab of diameter 50 feet supported on a circular wall of 8" thick and 38 feet outer diameter. The thickness of the slab is 28" (governed by shear design)

I am looking for a good example for two-way reinforcement detail. Can someone give me any suggestion on how to proceed. Thank you.

 

[BAretired]

What is the live load? Will the slab be 28" in the 6' cantilever as well?

BA

 

[sb79]

Loads on the Slab:

Self Wt of Slab = (145 lb/ft^3)* thickness (2.33') = 0.34 kips/ft^2
Wt of Water = 438000 Gal = (438000*8.33)/(pi/4*48^2)=2.02 kips/ft^2 ------------- (8.33 is the conversion of Gal to lb and 48 is the diameter of the steel tank). This load as the area load over 48' diameter

Wt of Steel Tannk = 40750 lb = 40750/(pi*d) = 40750/(pi*48) = 0.27 kips/ft

Wt. of Snow load = 30 psf (Act as a line load along the circumference of the tank) = (30*pi*48^2)/(pi*48) = 0.360 kips/ft

Note: For simplicity snow load is taken as dead load

Load Combination = 1.4*(Dead load+Water Load)

Hope this will clearly explain my whole problem

 

[BAretired]

For simplicity, I would suggest:
Provide two way bottom reinforcement for maximum positive moment. Provide two way top reinforcement for maximum negative moment. Provide nominal circumferential bars on edge of slab.

BA

 

[sb79]

BAretired: Yes, I am providing two way bottom reinforcement (for positive moment), two way top reinforcement (minimum reinforcement). Radial reinforcement for negative moment and circumferential reinforcement (minimum reinforcement based on shrinkage and temperature)

Please confirm my reinforcement detail

I got my negative and positive moment from RISA model. I want to check it with hand calculation. So is there anyway I can calculate moments for given loading.

 

[hokie66]

I would not use radial reinforcement. Just use orthogonal reinforcement, and the same result is achieved.

 

[JoshPlumSE]

I agree with Hokie. No need to get all fancy with your bar placement. Orthogonal bars work just fine.

Though, as BARetired suggests, a circumferential bar at the edge of the slab is a good idea. But, that's just to better control localized shrinkage cracking in locations where the orthogonal bars don't have sufficient development length.

 

[dik]

You should have the same moment resistance in both direction, modified for the slightly different depth to rebar centroid... This can be done for the +ve and -ve reinforcing. This way the slab has the same moment capacity in any direction... which you will have due to symmetry of a circular slab.