design of water tank

Design Of Water Tank & Sewage Treatment Plant For JNNCE Campus

INTRODUCTION

Dept. of Civil Engg., JNNCE

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Design Of Water Tank & Sewage Treatment Plant For JNNCE Campus

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.

Dept. of Civil Engg., JNNCE

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Design Of Water Tank & Sewage Treatment Plant For JNNCE Campus

SURVEY WORK OF THE CAMPUS

Dept. of Civil Engg., JNNCE

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Design Of Water Tank & Sewage Treatment Plant For JNNCE 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.

Dept. of Civil Engg., JNNCE

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Design Of Water Tank & Sewage Treatment Plant For JNNCE Campus

DESIGN OF OVER HEAD TANK

Dept. of Civil Engg., JNNCE

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Design Of Water Tank & Sewage Treatment Plant For JNNCE Campus

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.

Dept. of Civil Engg., JNNCE

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Design Of Water Tank & Sewage Treatment Plant For JNNCE Campus

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.

Dept. of Civil Engg., JNNCE

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Design Of Water Tank & Sewage Treatment Plant For JNNCE Campus

Dept. of Civil Engg., JNNCE

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Design Of Water Tank & Sewage Treatment Plant For JNNCE Campus

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 σcb = 7 N/mm2

m = 13 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.

Dept. of Civil Engg., JNNCE

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Design Of Water Tank & Sewage Treatment Plant For JNNCE Campus

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

Dept. of Civil Engg., JNNCE

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Design Of Water Tank & Sewage Treatment Plant For JNNCE Campus

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

Dept. of Civil Engg., JNNCE

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Design Of Water Tank & Sewage Treatment Plant For JNNCE Campus

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

Dept. of Civil Engg., JNNCE

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Design Of Water Tank & Sewage Treatment Plant For JNNCE Campus

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

Dept. of Civil Engg., JNNCE

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Design Of Water Tank & Sewage Treatment Plant For JNNCE Campus

Adopt d = 475mm & D = 500mm

b) Reinforcements in circular slab ; Using the above values of moments, the steel required is calculated.

Dept. of Civil Engg., JNNCE

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Design Of Water Tank & Sewage Treatment Plant For JNNCE Campus

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

Dept. of Civil Engg., JNNCE

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Design Of Water Tank & Sewage Treatment Plant For JNNCE Campus

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

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

Dept. of Civil Engg., JNNCE

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shear reinforcements are required

Design Of Water Tank & Sewage Treatment Plant For JNNCE Campus

d) Design of centre of span section ; Bending Moment, M=166.6 kNm

Provide 4-22 mm dia. bars (

DESIGN OF THE OXIDATION POND

Dept. of Civil Engg., JNNCE

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Design Of Water Tank & Sewage Treatment Plant For JNNCE Campus

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.

Dept. of Civil Engg., JNNCE

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Design Of Water Tank & Sewage Treatment Plant For JNNCE Campus

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 = 72 kg/day

Dept. of Civil Engg., JNNCE

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300

10-6

Design Of Water Tank & Sewage Treatment Plant For JNNCE Campus

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

Dept. of Civil Engg., JNNCE

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Design Of Water Tank & Sewage Treatment Plant For JNNCE Campus

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

Dept. of Civil Engg., JNNCE

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Design Of Water Tank & Sewage Treatment Plant For JNNCE Campus

CONCLUSIONS

Dept. of Civil Engg., JNNCE

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Design Of Water Tank & Sewage Treatment Plant For JNNCE Campus

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.

Dept. of Civil Engg., JNNCE

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Design Of Water Tank & Sewage Treatment Plant For JNNCE Campus

SCOPE FOR FUTURE STUDY AND IMPROVEMENT

Dept. of Civil Engg., JNNCE

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Design Of Water Tank & Sewage Treatment Plant For JNNCE Campus

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. .

Dept. of Civil Engg., JNNCE

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Design Of Water Tank & Sewage Treatment Plant For JNNCE Campus

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.

Dept. of Civil Engg., JNNCE

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