24-10-2016, 12:34 PM
1460789780-INTZTANKPPT.pptx (Size: 633.09 KB / Downloads: 6)
OBJECTIVE-
To study the variation
Of intze tank parameters using
Three grades of concrete M20,
M25,M30.
A water tank is used to store water to tide over the daily requirement. In the construction of concrete structure for the storage of water and other liquids the imperviousness of concrete is most essential .The permeability of any uniform and thoroughly compacted concrete of given mix proportions is mainly dependent on water cement ratio .
Intz tank-
Intze tank is found at for storage large volume of water and elevated circular tank provided with flat floor slab works out to an uneconomical design.
It is mainly on account of the fact at the floor slab becomes too thick for large diameter. Intz tank is best suitable under such circumstances.
Structural elements of intze tank
Top spherical Dome
Top ring beam
Bottom ring beam
Conical dome
Bottom spherical dome
Circular side walls
Bottom circular girder
Tower with columns and braces
Foundations
Design principles-
The r/f in the dome are designed for maximum meridional thrust and circumferential force.
The cross section area of the ring beam is determined by limiting the tensile stress in the ring beam to values specified in IS :456-2000 depending upon the grade of concrete .
The minimum thickness of 150-200 mm is provided of the top of the dome and thickness at the base of the vertical wall is designed by limiting the tensile stress.
Distribution and temperature r/f of .3% of the gross section is provided at the vertical direction.
The r/f in the ring beam are designed to resist the hoop tension and the section is designed limiting the tensile stress in concrete .
The r/f in the conical dome is designed for hoop tension and meridional thrust.
The design load for the dome includes the self weight of the dome and the weight of water column above the dome.
The column and brasses are design for maximum forces and moments develop due to the dead loads and wind loads acting on tower.
Cement Content –
1- The concrete used for tank should be a minimum of M25 grade mix so as to provide not only the strength but also higher density to prevent seepage .
2-The cement content should not be less than 300kg/m3 to get water tightness and not more than 530 kg/m3 to avoid cracking due to shrinkage of concrete .
3-A well graded aggregate with a w/c ratio less than 0.5 is recommended for making impervious concrete.
Permissible stress in steel-
1-HYSD steel r/f can be used in storage tanks.
2-The permissible stress in the r/f is controlled by the strain and crack widths rather than by the strength.
Minimum steel-
A minimum amount o steel shall always be provided in two principal direction to minimize cracking due to shrinkage temperature etc.
Spacing of steel -
For member upto 200 mm thickness ,the r/f may be provided in one layer and in members over 200 mm thickness, the steel should be equally divided on both faces.
The maximum spacing of steel is restricted to 300 mm.
For strength calculations:-
In strength calculations the permissible stress shall be as follows:
a) Tensile stress in member in direct tension 1000 kg/cm2.
b)Tensile stress in member in bending on liquid retaining face of members or face away from liquid for members less than 225mm thick 1000 kg/cm2.
c)On face away from liquid for members 225mm or more in thickness 1250 kg/cm2.
d)Tensile stress in shear reinforcement For members less than 225mm thickness 1000 kg/cm2 for members 225mm or more in thickness 1250 kg/cm2.
(e)Compressive stress in columns subjected to direct load 1250 kg/cm2.
Design in step-
The design of the tank will involve the following.
(1)The dome: at top usually 100 mm to 150 mm thick with reinforcement along the meridians and latitudes. The rise is usually l/5th of the span.
(2)Ring beam supporting the dome: The ring beam is necessary to resist the horizontal component of the thrust of the dome. The ring beam will be designed for the hoop tension induced.
(3)Cylindrical walls: This has to be designed for hoop tension caused due to horizontal water pressure.
(4)Ring beam at the junction of the cylindrical walls and the conical wall: This ring beam is provided to resist the horizontal component of the reaction of the conical wall on the cylindrical wall. The ring beam will be designed for the induced hoop tension.
Conclusion
It is found that for storing large volumes of water an elevated circular tank, provided with flat floor slab, works out to an uneconomical design. It is mainly on account of the fact that the floor slab becomes too thick for large diameters tanks. Intze tank is best suitable under such circumstances. An Intze tank essentially consist of a top dome (roof), the cylindrical wall and the floor slab, which is a combination of conical dome and bottom spherical dome.