The document describes the design of an Intze tank. An Intze tank consists of a top dome, cylindrical wall, and bottom dome combination used to store large volumes of water. The key steps in designing an Intze tank are: 1) designing the top dome, cylindrical wall, conical bottom dome, and supporting structures; 2) calculating loads and stresses; and 3) determining reinforcement requirements for each component based on strength calculations. An example is then given to design a specific Intze tank with given dimensions.

1. Intze Tank

2. It is used to store large volumes of
water at an elevation
• Intze Tank essentially consists of a Top
Dome (roof), the cylindrical wall and the
floor slab, which is a combination of
conical dome & bottom spherical dome.

3. Top Dome
Top Ring Beam
Cylindrical Wall
Bottom Ring Beam
Cylindrical Dome
Spherical Dome
Staging ( Columns)
Braces (Beams)

4. Design Procedure
• Design of Top Dome & Top Ring Beam
• Design of Cylindrical wall
• Design of ring beam @ the junction of the cylindrical
wall and conical dome
• Design of Conical Dome & Bottom Spherical Dome.
• Design of bottom ring beam
• Design of supporting structure, i.e., Staging
• Design of Foundation.
The design of Intze tank may be divided into following steps:-

5. • Principle: The proportions of the conical
dome & the bottom dome are so arranged
that the outward thrust from the bottom
domed part of the floor balances the
inward thrust due to the conical domed
part of the floor.

6. Dome: A dome may be defined as a shell
generated by the revolution of a curve about a
vertical axis.
If the curve of revolution is a segment of a circle,
the shell formed will be a spherical dome.
If the triangle is revolved about the vertical axis
then the shell formed is called as conical dome.

8. Stresses in a Spherical Dome:
The stresses to be considered in the design
of spherical dome are
• Meridional thrust (T),
T = wr (1-cosθ)/t sin2 θ
Meridional stress is max when θ = Φ
• Hoop Stress (H)
H = wr(cos2θ + cosθ – 1)/t (1+ cosθ)
Hoop stress is max when θ = 0
• Min thickness of the dome should be 100mm
and min Ast is 0.3 %

9. Stresses in a Conical Dome:
Meridional thrust (T)
T = wy/2t cos θ
Hoop Stress (H)
H = wy tan2θ /t

10. Ring Beam
A beam which is curved in plan is called ring beam.
It is to be designed for the horizontal component of the
stresses of above components
Tension = (T cosθ) D/ 2
Ast = Tension / σst

11. P. Design an Intze tank with dimension as shown
in fig. The tank is supported on 8 columns
braced at different levels. Use M20 grade of
concrete and mild steel. Take safe bearing
capacity of soil = 250 kN/m2

12. 10 m
3.75 m
3.75 m
3.75 m
3.75 m
14 m
1.6 m
1.8 m
6.0 m
1.68 m

13. Design of Dome
Assume the thickness of the dome slab = 100mm and
Live Load = 1.5 kN/m2
Load Calculations:-
Self wt of the dome = 25 x 0.1 = 2.5 kN/m2
Live Load = 1.5 kN/m2
Total Load = 4 kN/m2
Let r be the radius of the dome, then the relation between
the radius of the dome and the Tank : (2r-h) h =R2
h = ht of the dome = 1.8 m,
R = Radius of the tank = 7 m
Therefore r = 14.51 m

14. Max. Hoop stress in the dome is at θ = 0,
Hmax = wr/2t = 4 x 14.51 /(2 x .1x1000) = 0.29 N/mm2
Meridonal stress is max @ θ = Φ,
where Sin Φ = R/r
Φ = 280 50’
Mmax = wr (cos2 θ + cosθ – 1)/t (1+ cosθ) = 0.309 N/mm2
Area of Reinforcement = 0.2 % = 0.2 x 100 x 1000/ 100 = 200 mm2
Spacing of 8 mm Φ bars = 251 mm
Hence provide 8 mm Φ bars @ 250 mm c/c in both the directions.

15. Design of Top Ring Beam
Horizontal component of Meridional thrust,
p = Mmax Cosθ = 0.309 x 100 x 1000 x cos 28o 50’
Total tension, T = p.r = 189.49 kN
Assuming ring beam of size 400mm x 400 mm
Area of reinforcement required,
Ast = T / σst = 189.49 x 103 / 115 = 1648 mm2
No. of 20mm dia. bars = 6, Ast.prov = 6 x π /4 x 202
Check for tensile stress,
σct = T/ Area of concrete = 1.18 < 1.2 N/mm2, Hence safe.
Shear Reinforcement: Provide 2-legged 8 mm dia stirrups,
Spacing, S = 2.5 x Asv x fy / b = 157.08 mm2, say 150 mm c/c

16. Design of Cylindrical Wall
Note: Same as in case of walls of circular water tank hinged at base.
Max. Hoop Tension, Tmax = w h D/2 = .5 x 10 x 6 x 14 =420 kN
Area of reinforcement required,
Ast = T / σst = 420 x 103 / 115 = 3652.2 mm2
Thickness of wall, σc = T / ( t x 1000 + (m-1) Ast )  t = 305 mm
Hence provide 350mm thick wall.
As the thickness of the wall > 225 mm, the reinforcement is to be provided in two layers.
Reinforcement in each layer = 3652.2 /2 = 1826 mm2
Spacing of 16mm dia, s = AΦ x 1000/ Ast = 110 mm
Distribution steel,
For 450mm – 0.2 %
100mm – 0.3 %, for 350 mm 0.25 %,
Ast = 644 mm2 i.e., 344 mm2 on each face
Spacing of 10mm dia bars, s = 220 mm c/c

17. Design of bottom ring beam
Load calculations:
Load due to Top dome = Area of Slab x Meridional stress x Sin θ
= 100 x 1000 x 0.309 x Sin 280 50’ /1000
= 14.9 kN/m
Load due to Top ring beam = 0.4 x 0.4 x 25 = 4 kN/m
Load due to cylindrical wall = 0.35 x 6 x 25 = 52.5 kN/m
Self wt of beam = 0.75 x 0.75 x 25 = 14.1 kN/m
( assuming 750 x 750 mm size)
Total Load = 85.47 kN/m
Tension, P = w tanβ = 85.47 x tan 51.34 = 106. 84 kN
Hoop tension = pD/2 = 747.86 kN
Hoop tension due water pressure on ring beam = (w.h.d ) x D/2 = 252 kN
Total tension , T = 747.86 + 252 = 1000 kN
Ast = T / σst = 8695.66 mm2 ,  No. of 25 mm Φ = 18 nos
Shear Reinforcement :
2-legged -10mm Φ , s = 2.5 x Asv x fy / b = 2.5 x 78.5 x 250 / 750
= 125 mm c/c

18. Design of Conical Dome
Average diameter of conical dome = (14 + 10) /2 = 12
Avg depth of water = 6 + 1.68 / 2 = 6.84 m
Wt. of water above conical dome = 12 π x 6.84 x 10
= 5157.24 kN
Load from Top dome, cylindrical wall, ring beams
= 67.65 x π x 14
= 2975.4 kN
Self wt. of slab = 12 π x 2.61 x 0.55 x 25 = 1352.93 kN
( assuming 550mm thickness)
Total Load, W = 9485.57 kN
Load per m length @ base, w = W/(10π) = 301.935 kN/m
Max hoop stress in conical dome is given by
T = wy tan2θ/ 2t = 654.94 kN

19. Ast = T / σst = 5695.2 mm2
Ast on each face = 2848 mm2,
spacing of 20mm Φ bars = 110 mm c/c on each face
The conical dome also acts as a slab spanning between ring beam @
circular beam subjected to bending moment due to weight of water
and its self wt.,
w3 = (5157.24 + 1352.93) / (10π) = 207.225 kN
B.M = wL/12 = 207.225 x 2.61 / 12 = 45.07 kN.m
Ast = M/σst j d = 900.92 mm2
Min Reinforcement = 0.2 % = 0.2 x 550 x 1000 / 100 = 1100 mm2
Steel on each face = 550 mm2.
Hence provide 12mm Φ @ 200mm c/c on each face.

20. Design of bottom Spherical Dome
Assuming the thickness of dome slab = 300 mm
Radius of dome is given by ( 2R-h) = r2  2R = 52 + 1.6  R = 8.61m
SinΦ = r/R = 0.581 => Φ = 350 30’
Self wt. of the dome = 25 x 0.3 x 2π x 8.61 x 1.6 = 650 kN
Wt. of water = ( π /4 x 102 x ( 6 + 1.68) x 10 = 6031.86 kN
Total load = 6682 kN
Load per m = 6.682 kN/m
Max. Meridional thrust, M = wr / (1+cos θ) = 31.68 kN
Max. Meridional stress = 31.68 x 103/ (300 x 1000) = 0.11 N/mm2
Max. Hoop stress, H = wr/ 2t
= 6.682 x 6.81x 103 / (2 x 300 x 103) = 0.076 N/mm2
Providing Min Reinforcement
450mm – 0.2 %
100mm – 0.3 %, for 300 mm 0.243 %, Ast = 729 mm2
Spacing of 12 mm Φ, s = 130 mm c/c