Design of Elevated Level Storage Reservoir

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Design of Elevated Level Storage Reserviour

Tejaswi Koramutla1

Asst. Prof,

Annamacharya institute of technology and sciences, Rajampet. (Autonomous)

Anusha Sapatla2

Asst. Prof.

Annamacharya institute of technology and sciences, Rajampet. (Autonomous)

Abstract: Without water survival is impossible. Water is one of the most important substances on earth. All plants and animals must have water to survive. If there was no water there would be no life on earth. As water is very precious and due to the scarcity of drinking water in day to day life one has to take care of every drop.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 imperviousness1 of concrete is most essential. Overhead water tank is the most effective storing facility used for domestic or even industrial purpose. By considering all the requirements which are essential for economical2 construction, in this project an overhead tank is designed for AITS college population of around 4,419 members by manually and using software. The complete design of the elevated structure is given in the project by using LIMIT STATE METHOD from IS: 3370-20093.

Key words: Imperviousness, economical, IS:3370-2009

1 INTRODUCTION

Without water survival is impossible. Water is one of the most important substances on earth. All plants and animals must have water to survive. If there was no water there would be no life on earth. As water is very precious and due to the scarcity of drinking water in day to day life one has to take care of every drop. A water tank is used to store water for daily requirements like drinking, washing etc. An elevated water tank is a large water storage container constructed for the purpose of holding water supply at certain height to provide sufficient pressure in the water distribution system. Liquid storage tanks are used extensively used by municipalities and industries for storing water, inflammable liquids and other chemicals. These tanks have various types of support structures like RC braced frame, steel frame, RC shaft, and even masonry pedestal. The most commonly used staging in practice is the frame type. The main components of this type of staging are columns and braces. The staging acts like a bridge between the overhead container and foundation to transfer loads acting on the tank. Thus Water tanks are very important for public utility and for industrial structure and also to withstand more design forces. The frame support of the ELSR should have adequate strength to resist axial loads, moment and shear force due to lateral loads. These forces depend upon total weight of the structure, which varies with the amount of water present in the tank container.

    1. TYPES OF WATER TANKS

      The water tanks are majorly classified into water tank resting on ground, under the ground and the water tank about the ground. Based on the shape, water tanks are majorly circular rectangular and triangular shape. Elevated tanks are supported on staging which may consist of masonry walls, R.C.C. tower or R.C.C. columns braced together. The walls are subjected to water pressure. The base has to carry the load of water and tank load. The staging has to carry load of water and tank. The staging is also designed for wind forces. From design point of view the tanks may be classified as per their shape- rectangular tanks, circular tanks, intz type tanks. Spherical tanks conical bottom tanks and suspended bottom tanks. A circular shaped ELSR is adopted in this project for AITS College, Boyanpalli, Rajampeta, in Kadapa district in Andrapradesh.

    2. METHODOLOGY

      Limited cracking in the structure designed by working stress method was the main reason why the Indian Standard IS: 3370 (1965) did not adopt the limit state design method even after adoption by IS; 456 1978.However, with the following advantages of Limit State Design method, IS:3370 adopted Limit State Design Method in 2009.

      1. Limit State Design Method considers the materials according to their properties

      2. Limit State Design Method considers the load according to their nature

      3. The structures also fails mostly under limit state and not in elastic state

      4. Limit State Method also checks for serviceability

      IS: 3370-2009 Part (I-IV) adopts Limit State Design Method with precautions. It adopts the criteria for limiting crack width when the structures are designed by considering ultimate limit state and restricts the stresses to 130MPa in steel so that cracking width is not exceeded. These precaution ensures cracking width to be less than 0.2 mm i.e. fit for liquid storage. This also specifies clearly how a liquid storage structure differs with other structures.

    3. DESIGN METHODS USED

      As per discussion above, the three water tank design problems are designed by the following four design methods.

      1. Working stress method in accordance IS 3370 (1965).

      2. Working stress method in accordance IS 3370 (2009).

      3. Limit state design method with crack width calculations and check in accordance IS 3370 (2009).

      4. Limit state design method deemed to satisfy (limiting steel stresses) in accordance IS 3370 (2009).

    4. FLEXIBLE BASE CIRCULAR WATER TANK

      For smaller capacities rectangular tanks are used and for bigger capacities circular tanks are used .In circular tanks with flexible joint at the base tanks walls are subjected to hydrostatic pressure .so the tank walls are designed as thin cylinder. As the hoop tension gradually reduces to zero at top, the reinforcement is gradually reduced to minimum reinforcement at top. The main reinforcement consists of circular hoops. Vertical reinforcement equal to 0.3% of concrete are is provided and hoop reinforcement is tied to this reinforcement.

    5. PERMISSIBLE STRESSES IN CONCRETE Table: 1: Stress for different grades of concrete

      GRADE OF CONCRE TE

      DIRECT PERMISSIBLE STRESS IN

      KN/M^2 TENSION

      BENDING PERMISSIBLE STRESS IN

      KN/M^2 TENSION

      SHEAR

      M15

      1.1

      1.5

      1.5

      M20

      1.2

      1.7

      1.7

      M25

      1.3

      1.8

      1.9

      M30

      1.5

      2.0

      2.2

      M35

      1.6

      2.2

      2.7

      M40

      1.7

      2.4

      2.9

  1. DESIGN OF OVER HEAD WATER TANK

    The water tank is designed for the AITS college population of 4,475. Based on the per capita demand for institutional buildings the capacity of the water tank is reached as 100KL. The salient features of the overhead water tank is as tabulated below.

    Table: 2: Salient features of water tank

    Grade of Concrete : M20 Capacity of water tank : 100KL Staging of over head tank : 16m Number of columns : 6

    Number of braces : 3 Inner diameter of tank : 6 m Height of cylindrical walls : 4 m Rise of dome : 1.2 m

    Thickness of dome : 0.1 m Thickness of cylindrical walls : 0.18 m Dimensions of columns : 0.45 x 0.45m Dimensions of braces : 0.40 x 0.35m Top ring beam size : 0.2 x .2 m Bottom ring beam size : 0.3 x 0.2 m Thickness of floor slab : 0.1 m

    SBC of soil : 31.5t/m2

    Depth of footing : .37 m STRENGTH PARAMETERS

    Concrete Grade

    : M20

    Permissible stresses (from IS 3370{ part- 2}:2009)

    Direct tensile stress : 2.8 KN/m2 Direct compressible stress : 5 N/mm2

    Bending compressive stress (cbc) : 7 KN/m2 Characteristic compressive stress (fck) :20 N/mm2 Grade (for staging and sub structure)

    :H.Y.S.D Fe415

    Fig: 1: Circular shaped ELSR

    1. : POPULATION FORECASTING:

      Different methods of population forecasting are

      1. Arithmetic method

      2. Geometric method

      3. Incremental method

      4. Logistic method

      5. Graphical method

      By using geometric method population forecasted to 4,475. The total capacity of water required for the population is calculated as 100KL included with the fire demand.

      For the capacity obtained size of the tank is decided as Radius of the overhead tank: 3m

      Height of the overhead tank: 4m

    2. : Design of dome:

Minimum dome thickness must not be less than 100mm. Hence thickness of dome is assumed as 100mm.

Meridional Thrust T1=(WR/(cos+1)) Meridional stress =T1/(bXd)

Hoop stress = )

Meridional and hoop stresses developed in the spherical dome are 0.19N/mm2 and 0.04N/mm2 respectively. The obtained stresses are within the permissible stresses are the dome is safe against the stresses.

Total load on the dome is calculated as: 5 KN/m2 Factored load on the dome : 7.5 KN/m2

Providing minimum percentage of steel in the dome: Ast=

Table: 3: Reinforcement details in cylindrical side wall

Height above floor slab(m) (H2/Dt)

Heigh t below (M.W

.L)

Hoop coeffici ent

Hoop tensio n (KN)

Ar ea

(mm2)

Bo th

faces

Reinforceme nt

on each face

Propose d area

(mm2

)

No

.of bar s

spacin g

4

0.0H

0.0002

0.152

0.1

10

200

392

3.6

0.1H

0.0989

7.526

49.87

10

200

785

3.2

0.2H

0.1991

15.15

100

10

200

785

2.8

0.3H

0.3042

22.14

153

10

150

1046

2.4

0.4H

0.4137

31.48

209

10

140

1611

2

0.5H

0.5318

40.46

268

10

130

1740

1.6

0.6H

0.6408

48.76

323

10

130

1740

1.2

0.7H

0.6849

52.12

345

10

120

1884

0.8

0.8H

0.5779

39.41

261

10

120

1884

0.4

0.9H

0.2620

19.93

132

10

120

1884

Height above floor slab(m) (H2/Dt)

Heigh t below (M.W

.L)

Hoop coeffici ent

Hoop tensio n (KN)

Ar ea

(mm2)

Bo th

faces

Reinforceme nt

on each face

Propose d area

(mm2

)

No

.of bar s

spacin g

4

0.0H

0.0002

0.152

0.1

10

200

392

3.6

0.1H

0.0989

7.526

49.87

10

200

785

3.2

0.2H

0.1991

15.15

100

10

200

785

2.8

0.3H

0.3042

22.14

153

10

150

1046

2.4

0.4H

0.4137

31.48

209

10

140

1611

2

0.5H

0.5318

40.46

268

10

130

1740

1.6

0.6H

0.6408

48.76

323

10

130

1740

1.2

0.7H

0.6849

52.12

345

10

120

1884

0.8

0.8H

0.5779

39.41

261

10

120

1884

0.4

0.9H

0.2620

19.93

132

10

120

1884

0.3% (cross sectional area)

=300mm2

Hence provided reinforcement: 8mm Ø bars of 190mmc/c

Fig : 2 : Meridional and hoop stresses in spherical dome.

    1. : DESIGN OF TOP RING BEAM:

      Horizontal components of thrust(Ht) = T1xcos Hoop tension in ring beam(Ft) = Ht x(D/2) Tensile stress =

      Area of concrete calculated as 607mm2

      Hence provided a ring beam of size 200X200mm Total load on top ring beam = 7.5 KN/m2 Reinforcement provided as 4 nos of 20mm Ø bars.

    2. : DESIGN OF CYLINDRICAL WALL:

The reinforcement details of the cylindrical side wall with a hoop tension of 76.1KN was given as tabulated below

    1. : DESIGN OF BOTTOM RING BEAM:

      Horizontal thrust, H = T 1

      =

      = V1cot

      Tension due to vertical loads Hg = HD/2

      Hoop tension due to water pressure HW = Total load on bottom ring beam = 7.5KN

      Total factored load = 114.75

      KN/m

      Total Hoop tension on bottom ring beam=hoop tension due to vertical loads+ hoop tension due to water pressure

      = 389 KN

      The main reinforcement provided as 8nos of 20mmØ @ 120mm c/c.

    2. : DESIGN OF CIRCULAR SLAB:

      For every of the elevated water tank options, the base slab characteristic serviceability uniformly distribute load in kN/m per meter was the sum of its dead load, self-weight concrete and its finishing loads , and its live load, that is, the weight of water to be contained. And the serviceability point load in kN / meter, acting on each of the base slabs, at the extremes of the overhangs was derived by adding up the wall dead load that is the base projection weight and a calculated fraction of the top slab load. But some notice difference may be experience in the calculations of the fractions of the loads from the circular water tank top slabs. Thickness of circular slab =100mm

      Clear span of the slab = 6m

      Total load on the slab = 43.5 KN/m2 Total factored load on the slab = 62.25KN/m2

      Note : For every 1 m increase/decrease in length of compound wall the increase / decrease in basic rateof capacities from 500 to2500 KL as follows.

      500KL=0.086% , 1000KL = 0.047%

      0.00

      20.8

      8

      Add contractors profit @ 13.615%

      2.02

      Total rate

      Provision Towards VAT @ 5%

      0.84

      Provision Towards Labor Cess@1%

      0.17

      Note : For every 1 m increase/decrease in length of compound wall the increase / decrease in basic rate of capacities from 500 to2500 KL as follows.

      500KL=0.086% , 1000KL = 0.047%

      0.00

      20.8

      8

      Add contractors profit @ 13.615%

      2.02

      Total rate

      Provision Towards VAT @ 5%

      0.84

      Provision Towards Labor Cess@1%

      0.17

      Moment Mu = (Wa2/6) Ast provided as 412mm2

      The reinforcement provided in the slab was 10mm Ø @

      190mm c/c

    3. : DESIGN OF COLUMNS:

      Size of the column = 450X450mm Total vertical load on column =445.46 KN Wind intensity = 1.5 KN/m2 Number of columns = 6

      Moment at column base = 13.5 KN/m

      Reinforcement provided was 6nos of 20mm Ø @ 300mm c/c

      TOTAL RATE : 23.91 PER LITRE

      Total rate for 100 KL ELSR=23.91*100*100/10000 RS.23.91 Lakhs

    4. : DESIGN OF BRACINGS:

      Number of bracings = 6

      Size of bracings = 400X350mm Provide 4 bars of 16 mm diameter.

    5. : DESIGN OF FOOTINGS:

      Soil bearing capacity for the soil was 31.5t/m2 Total load on the footing = 396KN

      Total factored load = 594KN

      Size of the footing was decided as 1.4X1.4m

      Provide 5nos of 12mm Ø @ 220mm c/c.

      Unit

      Description

      Rate

      Tota l amo unt

      Rate for 100KL ELSR

      20.50

      Rate for 500 KL ELSR

      18.27

      Rate for 1000KL ELSR

      15.10

      Rate for 100 KL ELSR

      20.5

      0

      For 16Mts Staging

      For staging more than 15 Mt , the Rate shall be increased by Rs.0.10 Paisa on basic rate per every meter increase in staging

      0.10

      For SBC of 14.0 T/sq m

      For every decrease of 2.50 T/Sq m of SBC the rate shall be increased by 2.5%bon basic rate and for every increase of 2.5 T/Sq m of SBC the rate shall be decreased by 0.1% on basis rate

      – 0.70

      Wind pressure

      The above rate are applicable for wind pressure up to 350Kgs/Sq m for every 100 Kg/Sq m decrease in wind pressure the rate is to be decreased by 5%

      (PH SSR item No. 43 (11) ) formula =

      Basis

      – 1.51

      Cement variation

      The above rate shall be increased / decreased due to increase/decrease in cost of cement by basic rate * (6400-4000)*0.00007(PH SSR item No.43(7))

      2.54

      Steel variation

      The above rate shall be increased / decreased due to increase/decrease in cost of steel by basic rate (42000-46500)*0.00002

      – 1.36

      Unit

      Description

      Rate

      Tota l amo unt

      Rate for 100KL ELSR

      20.50

      Rate for 500 KL ELSR

      18.27

      Rate for 1000KL ELSR

      15.10

      Rate for 100 KL ELSR

      20.5

      0

      For 16Mts Staging

      For staging more than 15 Mt , the Rate shall be increased by Rs.0.10 Paisa on basic rate per every meter increase in staging

      0.10

      For SBC of 14.0 T/sq m

      For every decrease of 2.50 T/Sq m of SBC the rate shall be increased by 2.5%bon basic rate and for every increase of 2.5 T/Sq m of SBC the rate shall be decreased by 0.1% on basis rate

      – 0.70

      Wind pressure

      The above rate are applicable for wind pressure up to 350Kgs/Sq m for every 100 Kg/Sq m decrease in wind pressure the rate is to be decreased by 5%

      (PH SSR item No. 43 (11) ) formula =

      Basis

      – 1.51

      Cement variation

      The above rate shall be increased / decreased due to increase/decrease in cost of cement by basic rate * (6400-4000)*0.00007(PH SSR item No.43(7))

      2.54

      Steel variation

      The above rate shall be increased / decreased due to increase/decrease in cost of steel by basic rate (42000-46500)*0.00002

      – 1.36

    6. : ESTIMATION OF OVERHEAD WATER TANK

3. CONCLUSION:

Elevated water tanks provide head for supply of water. When water has to be pumped into the distribution system at high heads without any pumps for supply however pumps are necessary for pumping only till tank is filled. Once it is stored in tank the gravity creates the pressure for free, unlike pumps. We need pressurized water to fledge and make taps eject water at an appropriate rate. Elevated tanks do not require continuous operation of pump, as it will not affect the distribution system since the pressure is maintained by gravity. Strategic location of tank can equalize water pressure in the distribution system. The design of overhead tank is designed manually and a rough estimation for the proposed water tank is included.

REFERENCES

  1. IITK-GSDMA Guidelines for Seismic Design of Liquid Storage Tanks 2007.

  2. Chirag N. Patel & H. S. Patel, Supporting systems for reinforced concrete elevated water tanks: a state-of-the-art literature review, International Journal of Advanced Engineering Research and Studies, Vol. II, Issue I, Oct-Dec, 2012, 68-71,E-ISSN 22498974.

  3. IS: 11682-1985 Criteria for design of RCC staging for over head water tanks, Bureau of Indian Standards, New Delhi.

  4. S. K. Jangave et al., (2014). STRUCTURAL ASSESSMENT OF CIRCULAR OVERHEAD WATER TANK BASED ON FRAME STAGING SUBJECTED TO SEISMIC LOADING. Research gate, July 2014

  5. Reinforce concrete structures (Dr B.C PUNMIA).

  6. Reinforced concrete design (RAMAMRUTHAM)

  7. IS: 3370 1965 Code of practice for concrete structure for

    storage of liquids parts 1, part 2, part 4, BIS. New Delhi.

  8. IS:875-1987 Code of Practice for Design Loads parts 3, BIS.

    New Delhi

  9. N. Krishnaraju. Advanced Reinforced concrete Design, CBS

    publisher and distributors, New Delhi.

  10. IS: 456 2000 Code of practice for plain and Reinforced

    Concrete, BIS New Delhi.

  11. Bhandari M, Singh Karan Deep (2014), Comparative study of design of water tank, 231- 238

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