Friday, May 15, 2015

Reinforced Concrete Floor System

Circular Slab

Uses of Circular Slabs:

1.Roof of a room or hall circular in plan
2.Floor of circular water tanks or towers

3. Slab of a heli-port
4. Roof of pump houses constructed above tube-wells
5. Roof of a traffic control post at the intersection of roads

Concrete calculation of circular slab: 

Two links of concrete calculation (concrete calculator)of circular slab are given below:  

 Concrete estimation calculator



Following are the formulas to calculate how much concrete you will require for a circular slab:
3.14 x r (feet) x r (feet) x T (inches) ÷ 12 = cubic feet of concrete (CF)

Number of bags of concrete needed:

CF ÷ 0.45 = number of 60 lb. bags

CF ÷ 0.6 = number of 80 lb. bags

Number of cubic yards of concrete needed:

CF ÷ 27 = cubic yards

r = radius of the circle in feet (1/2 of the diameter)

T = Thickness in inches

CF = Cubic feet of concrete

[Note:
A 60 lb. bag provides 0.45 cubic feet of cured concrete.
A 80 lb. bag provides 0.6 cubic feet of cured concrete.
If you have concrete delivered it is sold by the yard (which is a cubic yard = 27 cubic feet)]

Example:
A circle 6" thick where the circle has a radius of 5.5' (11' diameter circle)
3.14 x 5.5 x 5.5 x 6 ÷ 12 = 47.5 cubic feet of concrete
47.5 ÷ 0.45 = 106 (105.6) 60 lb bags of concrete
47.5 ÷ 0.6 = 80 (79.2) 80 lb. bags of concrete
47.5 ÷ 27 = 1.8 cubic yards of concrete

Design of a Circular Slab:

Simply supported slab with uniformly distributed load:

 




Reinforcement in Circular Slab:






Some Images of Circular Slab reinforcement:



Example (Basically Water Tank):
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).
 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)

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