CHAPTER 7 WATER TANK
As per Greek philosopher Thales, “Water is the source of every creation.” In day to day life one cannot live without water. Therefore water needs to be stored for daily use. Over head water tank and underground water reservoir is the most effective storing facilities used for domestic or even industrial purpose. Depending upon the location of the tank the tanks can be named as overhead, on ground or underground. The tanks can be made in different shapes usually circular and rectangular shapes are mostly used. The tanks can be made of RCC or even of steel. The overhead tanks are usually elevated from the roof top through column. In the other hand the underground tanks are rested on the foundation. Different types of tanks and their design procedure is discussed in subsequent portion if this chapter. The water tanks in this chapter are designed on the basis of no crack theory. The concrete used are made impervious.
TYPES OF WATER TANK
Basing on the location of the tank in a building s tanks can be classified into three categories. Those are: • • • Underground tanks Tank resting on grounds Overhead tanks
In most cases the underground and on ground tanks are circular or rectangular is shape but the shape of the overhead tanks are influenced by the aesthetical view of the surroundings and as well as the design of the construction. Steel tanks are also used specially in railway yards. Basing on the shape the tanks can be circular, rectangular, square, polygonal, spherical and conical. A special type of tank named Intze tank is used for storing large amount of water for an area. The overhead tanks are supported by the column which acts as stages. This column can be braced for increasing strength and as well as to improve the aesthetic views.
BASIS OF DESIGN
One of the vital considerations for design of tanks is that the structure has adequate resistance to cracking and has adequate strength. For achieving these following assumptions are made: • Concrete is capable of resisting limited tensile stresses the full section of concrete including cover and reinforcement is taken into account in this assumption. • To guard against structural failure in strength calculation the tensile strength of concrete is ignored. • Reduced values of permissible stresses in steel are adopted in steel are adopted in design.
The simplest from of water tank is circular tank for the same amount of storage the circular tank requires lesser amount of material. More over for its circular shape it has no corner and can be made water tight easily. It is very economical for smaller storage of water up to 20000000 liters and with diameter in the range of 5 to 8 m. The depth of the storage is between 3 to 4 m. The side walls are designed for hoop tension and bending moments.
7.4.1 PERMISSIBLE STRESSES IN CONCRETE
To ensure impervious concrete mixture linear than M 20 grade is not normally recommended to make the walls leak proof the concretes near the water face need to such that no crack occurs. To ensure this member thicknesses are so designed that stress in the concrete is lesser then the permissible as given in table 7.1.
THE PERMISSIBLE STRESS IN STEEL
The stress in steel must not be allowed to exceed the following values under different positions to prevent cracking of concrete. • When steel is placed near the face of the members in contact with liquid 115 N/ sq mm for ms Bars and 150 N/ sq mm for HYSD bars. • When steel is placed on face away from liquid for members less then 225 mm in thickness same as earlier. • When steel is placed on the face away from the liquid for members 225 mm or more in thickness: 125 N/ sq mm for M.S. bars and 190 N/sq mm for HYSD bars.
Table 7.1 Permissible Stresses In Concrete (For calculations relating to resistance to concrete)
Permissible Stresses Grade of...
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