design of water tank

Design Of Water Tank & Sewage Treatment Plant For JNNCE Campus

INTRODUCTION

Dept. of Civil Engg., JNNCE Page 1


1. INTRODUCTION

Jawaharlal Nehru National College of Engineering is a prestigious institution managed by

National Education Society. It is located on the outskirts of Shimoga city, at about 4km from the

heart of the city. The college campus is spread over an area of about 52 acres.

It was established in 1980, by great visionaries & freedom fighters, with the intention of

imparting technical education to the ambitious students of the region. The college which had less

than 100 students in the beginning has now after 28 years more than 3000 students studying in it.

The college has grown both in terms of infrastructure & the educational standards. Presently it is

one of the most sought after engineering colleges in Karnataka. Apart from engineering, various

P.G courses such as M.Tech, MBA, MCA have also been started and recently Polytechnique

courses have also been started, thus increasing the student strength even more.

The college, in these 28 years has shown a slow & steady growth. With this growth the

demand for better infrastructure also grew. As and when the requirement arose, new buildings

were constructed. Each time a new building was constructed, separate water connection was

given and each building was provided separate overhead tank and sump arrangement. Thus the

college as of now doesn’t have a single water supply and distribution system.

Thus in this project an attempt has been made to design a water tank and a sewage

treatment plant for the entire campus assuming that the college was actually planned to have

been developed in this manner.

The project work consisted of the following

1. Survey work of the campus.

2. Design of water tank.

3. Design of oxidation pond.



SURVEY WORK OF THE CAMPUS



2. SURVEY WORK OF THE CAMPUS

Detailed survey of the campus was carried out for about 20 days using the Total Station.

Total Station is a single instrument which can be used to perform all the steps involved in the

survey work such as leveling, distance and angle measurements etc., with high level of accuracy.

The survey work was carried out by rectangular coordinate method using the plinth level

of the administrative block as the reference Bench Mark with an RL 100.00m.

In the rectangular coordinate method each point is assigned its rectangular coordinates in

all three dimensions, so that all the points can easily be plotted using a software such as AutoCad

and since the level of the point is also recorded, the ground profile can also be known for a series

of points, which facilitates the location of highest or least RL.

Thus in course of the survey, important points such as building corners, road edges,

points on curves, diversion points on compound wall etc., were recorded, cross checking the

work with other accessories such as tape at regular stages of the work, so that all the information

necessary for the planning stage were made available.

After the survey work, the data in the form of points and their coordinates was transferred

to the computer from the instrument. Then using these points, the layout of the college was

prepared using AutoCad software.



DESIGN OF OVER HEAD TANK



3. DESIGN OF OVER HEAD TANK

After deciding the location of the tank, next step was to design the tank. It was decided to

go for a flat bottomed RCC circular overhead tank, with 6 columns and bracings forming the

staging, because of its easy and convenient design procedure.

Before going for the actual design, certain data required for the design were collected

which included the admission data of students, hostel intake, number of staff- both teaching and

non teaching etc. After analyzing the collected data, the average student strength of 2008 & 2009

batch was taken as the design strength since there was 15% rise in student intake from the year

2008 onwards.

3. 1 Site selection for OHT

After the layout of JNNCE was prepared, the points of highest RL and lowest RL were

located on it. Also it was observed that at these points the conditions were suitable for the

location of the water tank and the oxidation pond respectively.

Some of the factors considered for the site selection of water tank were as follows

1. The site should be located preferably at the point of highest RL.

2. Sufficient space or area should be available without any horizontal or vertical

restrictions.

3. Hard soil should be available at shorter depth with required SBC

4. The site should be preferably located closer to the builtup area so that the length

of the pipeline required for conveyance & distribution gets reduced.

Taking into account all these factors, the water tank was decided to be located near the

administrative block as shown in the college layout where almost all of the above conditions are

satisfied.



3.2 Estimation of water requirement

I) No. OF STUDENTS

B.E - (630 x 4)

P.G - (130 x 2)

Diploma - (150 x 3)

TOTAL - 3230

II) No. OF STAFF - 350

TOTAL - 3580

III) HOSTEL STRENGTH - 570

From National Building Code of India : Part IX-1, Cl. 5.2

Daily water supply ; 1) For educational institutions = 45 lpcd

2) For Hostels = 135 lpcd

Hence water supply required = (3580 x 45) + (570 x 135)

= 2,38,050 liters

Increasing this by a factor 1.25,

Total water requirement = 2,97,562 liters

Hence Volume of water req. = 3,00,000 liters.



3.3 Design of OHT

3.3.1. DATA :

Capacity of tank = 300 m3

Grade of concrete = M20

Grade of steel = Fe415

Method adopted – WORKING STRESS METHOD

3.3.2. PERMISSIBLE STRESSES :

From IS:3370 stresses relating to resistance to cracking are ;

σct= 1.2 N/mm2 σst= 150 N/mm2

For strength calculations, stresses in concrete and steel as recommended in IS:456 are ;

σcc = 5 N/mm2 m = 13

σcb = 7 N/mm2 Q = 1.14

j = 0.897

3.3.3 Dimensions of the tank :

Let D = inside diameter of the tank. Assuming an avg. depth of 0.6D, we have

Provide a free board of 0.2m, hence height of the cylindrical portion=5m.



3.3.4. DESIGN OF TOP DOME :

Adopt thickness of dome slab = t = 100mm

Live load on dome = 1.00 kN/m3

Self weight of dome = (0.1 x 24) = 2.4 kN/m3

Finishes = 0.2 kN/m3

If, R = Radius of the dome.

D = Diameter at the base (=9m)

r = Central rise (=1.5m)

Now , cos θ = (4.5 / 6) = 0.8



Since the stresses in dome are within safe permissible limits, provide nominal reinforcements of 0.3%

Provide 8 mm dia. bars @ 160 c/c , both circumferentially & meridionally.

3.3.5. DESIGN OF TOP RING BEAM :

Provide 4- 12 mm dia. bars [Ast = 452 mm2], with 6mm dia. stirrups @150 c/c(nominal).

If, Ac = c/s area of ring beam , we have

Solving we get Ac = 39,576 mm2

Hence adopt a ring beam of size 210mm by 210mm



3.3.6. DESIGN OF CYLINDRICAL TANK WALL :

For the tank H=5m, D=9m

Since maximum Hoop tension occurs @ 0.6H (=3m) from the top

From IS:3370, table 17.2(a), hoop tension coefficient = 0.639

Provide 16mm dia. bars @ 200 c/c along the outer face of the tank

From IS:3370, table 17.2(b),

the maximum –ve moment occurs @ the base, co-efficient for –ve moment = 0.0090

Maximum +ve moment occurs @ 0.7H from the top, coefficient for +ve moment = 0.0019



= 0.0019 x 10 x 52

= 2.375 kNm

Also vertical distribution steel = 0.3 %

3.3.7. DESIGN OF TANK FLOOR SLAB :

The tank floor slab is circular & is fixed on the periphery to the circular ring beam.

Load on the circular beam = w

= (Weight of water) + (Self weight of slab assumed as 450mm)

w = (10 x 4.8) + (0.45 x 24)

w = 58.8 kN/m

a) Maximum radial & circumferential moments ;

Positive moment at the centre of span is

Negative moment at the supports is

Circumferential moment is given by



Adopt d = 475mm & D = 500mm

b) Reinforcements in circular slab ;

Using the above values of moments, the steel required is calculated.



3.3.8. DESIGN OF BOTTOM RING BEAM :

a) Total load on the ring beam;

Weight of water = 3000 kN

Load from dome = (2πRrw) =254 kN

Weight of top ring beam = (π x 9.21 x 0.21 x 0.21 x 24) = 30.62 kN

Weight of cylindrical wall = (π x 9.2 x 0.2 x 5 x 24) = 693.6 kN

Weight of floor slab = (π x 4.52 x 0.475 x 24) = 725.24 kN

Weight of bottom ring beam(assuming a .4 x .6 section) = (π x 9.2 x 0.4 x 0.6 x 24)

= 124.8 kN

b) Moment and shear forces in the ring beam;

Assuming six columns supporting the ring beam, the moments are as follows;

Negetive B.M at the supports = 0.0148 WR

= 0.0148 x 4830 x 4.6

= 328.8 kNm

Positive B.M at the centre of span b/w supports = 0.0075 WR

= 0.0075 x 4830 x 4.6



= 166.635 kNm

c) Design of support scetion ;

Bending moment = M = 328.8 kNm

Shear force = V = 402.5 kN

Adopt d = 900 mm and overall depth = 950 mm

Provide 4-32 mm dia. bars (Ast = 3217 mm2)

From IS:456, table 23 , = 0.372 N/mm2 shear reinforcements are required

Using 12 mm dia. 2L stirrups, the spacing is given by



d) Design of centre of span section ;

Bending Moment, M=166.6 kNm

Provide 4-22 mm dia. bars (

DESIGN OF THE OXIDATION POND



4. DESIGN OF THE OXIDATION POND

Oxidation pond combines the features of the aerobic and anaerobic ponds. Constructed of

intermediate depth (1.0m to 1.5m) , an oxidation pond consists of three zones; (a) aerobic zone at

the top, (b) anaerobic zone at the bottom, (c) facultative zone situated between the aerobic and

anaerobic zones, where decomposition of incoming organic wastes and products of anaerobic

decomposition are done by facultative bacteria. The aerobic layer acts as a good check against

odour evolution from the pond. The pond depth inhibits mixing; hence organic solids which

settle will remain on the bottom and will be subjected to anaerobic decomposition. The treatment

effected by this type of pond is comparable to that of conventional secondary treatment

processes. Hence the oxidation pond is best suited and most commonly used for treatment of

sewage.

4.1 Site selection for oxidation pond

The site for the oxidation pond was decided considering the following

1. The site should be located preferably at the point of least RL.

2. Sufficient space or area should be available without any horizontal or vertical

restrictions.

3. It should be located nearer to the compound or boundary so that the disposal

of treated effluent becomes easy.

4. A water body such as a pond, lake or stream must be situated near the site so

that the disposal becomes easy.

Considering all these factors the oxidation pond was decided to be located near the

compound wall beside the Thunga hostel as shown in the layout, where all of these conditions

are satisfied. Moreover a pond is located just outside the compound wall facilitating easy

disposal of the treated effluent.



4.2. Design of oxidation pond

4.2.1. Data

Location or Latitude of the site [SHIMOGA] = 14 N

Elevation = 600 m [Above MSL]

Mean monthly temperature = 30 c max & 10 c min

Now assuming 80% of water supplied to be converted as sewage,

Total sewage flow to be treated = 0.8 3, 00,000

= 2, 40,000 liters/day

Hence the total sewage flow = 240 m3/day

Also the desired effluent BOD = 30 mg/day

Assuming the sewage produced as purely domestic,

It’s initial BOD5 = 300 mg/l [avg. strength]

Pond removal constant @ 20 c = 0.1/day

4.2.2. Total BOD Load

Total BOD load on the OXIDATION pond = 2, 40,000 300 10-6

= 72 kg/day



4.2.3. Permissible areal BOD Loading

Areal BOD loading @ 14 latitude = 287.5 kg/ha.day (from IS:5611)

Correction factor for elevation = 1+0.003 EL

[Assuming that the sky is clear for 60% of days of an year]

= 270.255 kg/ha.day

4.2.4.Pond Area

4.2.5. Detention Period

Pond removal constant @ 10 c (min temp)

= 0.06317/day



4.2.6. Pond Volume & Depth

Total inflow = 240 m3/day

4.2.7. Pond System

Total pond area= 0.2664 ha = 2664m2

Adopt rectangular ponds with length to breadth ratio as 2.5

Hence provide a pond of area (81 33) m2,

Therefore actual area provided =2673m2



CONCLUSIONS



5. CONCLUSIONS

1. The capacity of the OHT required is 300 m3.2. The size of the oxidation pond required is 81m X 33m.3. The project work is a case study where an attempt has been made to design the OHT and

oxidation pond to fulfill the requirements of the institution for another decade.4. The site-map of the college prepared for this project can be used as a reference map for

the future planning of the campus.



SCOPE FOR FUTURE STUDY AND IMPROVEMENT



6. SCOPE FOR FUTURE STUDY AND IMPROVEMENT

It was possible to prepare the layout of the campus and design the water tank and oxidation pond in the limited time. The following works are to be completed for the satisfactory functioning of the system.

1. The design of staging for the water tank.2. Design of the distribution system for the water supply.3. Design of Underground Drainage system to carry the sewage to the oxidation pond.

.



7. REFERENCES

1. National Building Code of India.

2. IS:3370 -Indian Standard Code of practice for concrete structures for the storage of liquids.

3. IS:456-Indian Standard Code of practice for Plain & Reinforced Concrete.

4. SP-16-Design Aids for Reinforced Concrete to IS:456.

5. IS:5611-Indian Standard Code of Practice of stabilization of ponds.

6. “Design of R.C. Structures” by Krishna Raju.

7. “Waste Water Management” by B.C.Punmia , S.K.Jain & A.K.Jain.

8. “Concrete Structures” by V N Vazirani & M M Ratwani.


design of water tank

Documents

jnnce campus design

jnnce campus survey

design strength

college campus

jnnce page

actual design

site selection of water

jnnce campus introduction