Minor Project

Major project

ANALYSIS AND DESIGN OF UNDERGROUND STORAGE TANKS OF POLYETHYLENE AND POLYMERS Guide Dr.B.S.Munjal

Makadia Hiral R. (06MCL007)

Space Application Center (SAC/ISRO) SPECIAL THANKS TO DR H V TRIVEDI SIR FOR INTERFACING WITH M/S SINTEX INDUSTRIES, KALOL FOR A RESEARCH PROBLEM

INTRODUCTION • Polyethylene tanks are used for liquid storage purpose. • It is generally used as water tank in building. • Polyethylene water tanks are placed above building or on the ground, • Nowadays these kinds of tanks are used for liquid storage but it is embedded in ground. These tanks are also used for purpose of septic tank

• These tanks are having more advantages in compare to other conventional underground tank. • These tanks are pre-fabricated just installation at site is required for use. • Tanks can be manufactured for different capacity according to use. • Septic tank is also a underground storage tank to retain waste from house.

• In India underground tanks are constructed by conventional method, with concrete or masonry. (septic tank)

• Nowadays plastic products (polyethylene products) are used for manufacturing of underground tanks.

Advantages of polyethylene tanks • Material (polyethylene) used for manufacturing are Eco friendly. • Rust proof. • Tanks are leak proof. • septic tanks are light in weight. • Easy to install, • Economical than conventional septic system.

LITERATURE SURVEY Bloys Rijkmans. ICO Courtenary. “The significance of creep in designing with plastic” Jumping curve magazine, Issue June 06.

[1]

• Stress-strain relationship is derived for finding information about tensile strength, elongation, flexural modulus and perhaps impact properties. Design tanks with, for example 900% elongation combined with a tensile stress at yield of 170Mpa.

Test sample are subjected to a load and

the strain measured over time at a set temperature.

• The FE analysis can predict how parts will behave over long time periods and highlight areas of high stress due to design or loading conditions. The rib in tank wall provides some rigidity to the tank wall but also changes the stress intensities within the tank.

[2] R. Sturt, L. Shipley, A. Ghose and M. Hiremath “Dynamic analysis of highlevel waste storage tanks” ARES Corporation, Computer & Structures Vol 56. No. 2/3 ,1995.

[3] David Royalance “Finite element analysis” Department of Material science and Engineering. Massachusetts Institute of Technology, Cambridge. 2001 • Fundamental concept [K] {u} = {F}

{u} = [K]-1{F} [K] {u} {F}

Property Behavior Action

• It is difficult to solve algebraic equation of entire domain, divide the domain in small simple element.

• FEA procedure by commercial software

[4] Prof. Oliver de Weck “Meshing in Finite Element Analysis” Open Class Work (OCW), Massachusetts institute of Technology.2006 • Types of mesh

Structured mesh

Unstructured mesh

•

Shape of meshing – Meshing should avoid both very sharp and wide angles.

•

Number of elements -

Number of elements should be moderate. Related to efficiency of finite element analysis –Convergence Studies .

Products of SINTEX industries

Water tanks of Polyethylene

Underground water sumps

underground water storage tank

Transportable water tanks

SCOPE OF WORK

• Finite element analysis of polyethylene underground tanks. • Analyses in Stress & deflection domains. • Analysis of underground tank for different loading conditions. • Deciding thickness of polyethylene wall. • Types of Stiffeners used in tank. • Placement of stiffeners (outside or inside). • Spacing of stiffeners. • Techno-Commercial design by considering all criteria.

Capacity used 3000 Litres & 5000 Liters

MODELING OF SEPTIC TANK •

Geometry of septic tank Geometry is decided with the use of capacity of the septic tank, dimensions are proposed with 5000 liters and 3000 liters capacities of underground storage tank. Depending on numbers of domestic users of tanks dimensions are decided.

Types of Stiffeners

Type-1

Type-3

Type-2

APPROACH SYNTHESIS • In this piece of work effort is made to design a techno-commercial concept of underground storage tank. • Using sensitivity approach, efforts are made to reach final design by varying different geometry parameters of the tank.

GEOMETRY: • Geometry is the basic parameter to decide initially. 1. Vertical cylindrical tank 2. Horizontal cylindrical tank RETENTION TIME:

THICKNESS OF TANK: • Thickness of tanks can be vary from 4mm to 6mm from practical aspects. MATERIALS: • Tank can manufactured from available polyethylene products. • Materials used for this work are HDPE, LLDPE and FRP (explanation follows).

STIFFENERS: • In case of plastic tanks stiffeners are the major requirement for structural stability. Stiffeners are provided with different shape, spacing, orientation etc. • • •

Shape of stiffeners Spacing of stiffeners Orientation of stiffeners

MATERIALS Materials used for this piece of work are • • •

Linear Low density polyethylene (LLDPE) High density polyethylene (HDPE) Fiber reinforced Polymers (FRP)

MATERIALS TESTING • Polyethylene materials are tested to find their mechanical properties. Testing is done on raw material as well as on molded sheet (Tests were conducted by M/S Sintex Industries) • Results have been used in sensitivity analysis ). • STANDARD TEST METHODS FOR TENSILE PROPERTIES OF PLASTIC (ASTM D 790-03)

Specimen for test

Testing on UTM

Breaking of specimen

400 350 300

Load in N

250 200 150 100 50 0 0

6

12

18

24

30

36

42

E long atio n in m m

48

54

60

Max load Elongation at max load % Elongation Elongation at break % elongation Tensile strength N/mm2

373.75 N 5.52 mm 22.08 72.41 mm 289.64 19.089

• STANDARD TEST METHODS FOR FLEXURAL PROPERTIES OF PLASTIC ASTM D 790-03

Shape of test specimen

Loading assemblies for testing

20 18

Max load Bending strength Flexural modulus

16 14

Load in N

12 10 8

17.956 N 4.373 N/mm2 615.89 N/mm2

6 4 2 0 0

1

2

3

4

Elongation in mm

LIMITING VALUES: Linear Low Density Polyethylene (LLDPE) High Density Polyethylene (HDPE) Fiber Reinforced Polymers (FRP)

22 MPa 43 MPa 132 MPa

LOADINGS • Loadings are basic requirement for analysis of any structures. • loadings are depending upon different parameters. • Tank system will be outside of house premises, so it is possible that some vehicles will be passing over it. • By considering all parameters, typical loadings furnished by M/S Sintex are explained in subsequent presentation.

Axle load Tractor axle GL Manhole W

Septic tank

Man + Animal load Man+cow load GL Manhole Septic tank

Liquid pressure GL Manhole Septic tank

Liquid pressure

Soil pressure GL Manhole

Soil pressure

Septic tank

500mm Soil load GL Manhole

500 mm Septic tank

• Above loadings are used in analysis. • All loads are not consider at a time for analysis. • Load combinations are carried out, after detailed discussions with Sintex Industries from practical point of view...

Results and discussions • Wide gamut of Analysis runs are made with different topologies of geometries and stiffeners positions and shapes to arrive at a technocommercial design needed by Sintex Industries... • Stresses and deflection analysis is carried out using finite element analysis software-ANSYS. • Results are presented for Sensitivity analysis.

Model-1 and mashed model

Boundary condition

All degree of freedom restrained at bottom

Load combinations Load Case-1 [1] [2] [3]

5500 N (550 Kg) – Man + Animal Load 0.0689 N/mm^2 (10 Psi)- Soil Pressure 500 mm soil over head load

Displacement contours model-1 Large value of deflection

Minimum stiffener case

Displacement in mm

Von misses stress (N/mm ) 2

Higher stress region

• • • • • • •

Load case-2 50000 N(5 ton)-tractor axle load 0.0689 N/mm^2-Soil Pressure 0.0620 N/mm^2-Liquid Pressure 500 mm soil load Load case-3 50000 N – tractor axle load 0.0689 N/mm^2 Soil Pressure 500 mm soil load

Displacement contour Model-1

Deflection in mm

Von misses stress (N/mm ) 2

Stress is higher 190 N/mm2

Model-2

Stiffeners Type-1

Type-2

1 2 2 1 2 2 1

Displacement contour Deflection reduced

Deflection in mm

Von misses stress (N/mm ) 2

Stress: 93.9 N/mm2

Def lection in model-1 Def lection in modle-2

1200

Deflection in mm

1000 800 600 400 200 0 0

0.5

1 1.5 2 Height of tank in m

2.5

3

Displacement comparisons for model-1 & model2 Von misses stresses in model-1

160

Von misses stresses in model-2

Stresses in Mpa

140 120 100

0.6 0.4 0.2 0

80 60 40 20 0 0

0.5

1

1.5

2

2.5

3

Height of tank in m

Displacement comparisons for model-1 & model2

UNDERGROUND TANKS TYPE-2 • Geometry was changed from vertical cylindrical tank to horizontal cylindrical tank. • In these tanks three types of models were prepared for investigation. • Tanks are also analyzed for different materials.

Geometries of tank type-2

Model-1 with minimum stiffeners

Model-2 with more stiffeners

Model-3 with inside stiffeners

Result contours

Displacement contours (Model-1)

Stress contours (Model-1)

Stress contours (Model-1)

LLDPE material (model-1) 400

120

376

102

300

245 180

200 100

Stress in MPa

Deflection in mm

100

Model-1

80 60

40

40

25.5

20 0

0 4

5 Thickness of tank in mm

4

6

5 Thickness of tank in mm

Deflection comparison

6

Stress comparison

LLDPE material (model-2) 127

40

120

35

100

30

75

80 60

45

40 20

Stress in MPa

Deflection in mm

140

37.8 30

25

21.7

20 15 10 5 0

0 4

5

6

Thickness of tank in mm

Deflection comparison

4

5

6

Thickness of tank in mm

Stress comparison

Model-2

LLDPE material (model-3) 151

160

60

52.7

50

120

Stress in Mpa

104

100 80

65

60 40

Model-3

45

40 30

24.6

20 10

20 0

0

4

5 Thickness of tank in mm

6

4

5 Thickness of tank in mm

Deflection comparison

6

Stress comparison

HDPE material (model-1) 140

60

137

50

120

98

100

90

80 60 40 20

Stress in Mpa

160 Deflection in mm

Deflection in mm

140

48 40

40

32

30 20 10

0 4

5

6

Thickness of tank in mm

Deflection comparison

0 4

5

6

Thickness of tank in mm

Stress comparison

HDPE material (model-2) 85

90

40

38

35

70

60.5

60

46

50 40 30 20

Stress in MPa

Deflection in mm

80

30

30 25

21

20 15 10

10

5

0 4

5 Thickness of tank in mm

0

6

4

Deflection comparison

5 Thickness of tank in mm

6

Stress comparison

HDPE material (model-3) 60

120 100

67

60

51

40

Stress in MPa

Deflection in mm

100 80

51

50 40 40

33.6

30 20 10

20

0

0 4

5 Thickness of tank in mm

6

Deflection comparison

4

5

6

Thickness of tank in mm

Stress comparison

FRP material (model-1) 2.5

10

1

Stress in MPa

1.65

1.5

0.5

5

7 6

6.05 4.5

5 4 3 2 1 0

0 4

9

9 8

1.9

6

4

Thickness of tank in mm

5

6

Thickness of tank in mm

Deflection comparison

Stress comparison

3000 liters tank is also analyzed for model-1 90

80

80 Stress in MPa

Deflection in mm

2 2

68

70 60 50 40

32

30 20 10 0 4

5

6

Thickness of tank in mm

Stress contours

Stress comparison

COMPARATIVE STUDIES • COMPARISON OF 5000 LITERS TANK (horizontal cylindrical tank) • LLDPE material 120

80 70 Stress in MPa

Deflection in mm

160 140 100 80 60 40 20

Model-1

90

THK 4 mm THK 5 mm THK 6 mm

180

THK 4 m m THK 5 m m THK 6 m m

60 50 40 30 20 10 0

0 0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

Height of tank in m

Deflection comparisons for tank model-1

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

Height of tank in m

Stress comparisons for tank model-1

Model-2 THK 4 mm THK 5 mm THK 6 mm

160 120 100 80 60 40

THK 4 mm THK 5 mm THK 6 mm

40 35 30 Stress in Mpa

Deflection in mm

140

25 20 15 10 5

20

0

0 0

0.2

0.4

0.6

0.8

1

1.2

1.4

0

1.6

0.2

0.4

0.6

Height of tank in m

0.8

1

1.2

1.4

1.6

Height of tank in m

Deflection comparisons for tank model-2

Stress comparisons for tank model-1

Model-3 160

THK 4 mm THK 5 mm THK 6 mm

120 100 80 60 40 20

THK 4 mm THK 5 mm THK 6 mm

45 40 Stress in Mpa

Deflection in mm

140

35 30 25 20 15 10 5 0

0 0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

Height of tank in m

Deflection comparisons for tank model-3

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

Height of tank in m

Stress comparisons for tank model-1

COMPARISONS FOR STIFFENERS SHAPE

Stiffener type-2

180 160 140 120 100 80 60 40 20 0

Stiffener type-1 Stiffener type-2

Stress in MPa

Deflection in mm

Stiffener type-1

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

Height of tank in m

Deflection comparisons for tank model-3

Stif fener type-1

50 45 40 35 30 25 20 15 10 5 0

Stif fener type-2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

Height of tank in m

Stress comparisons for tank model-1

Comparison for spacing of stiffeners

Model-1

Deflection in mm

140 120 100 80 60 40 20

With minimum stiffeners With more stiffeners

45 40 35 Stress in MPa

With minimum stiffeners With more stiffeners

160

Model-2

30 25 20 15 10 5 0

0 0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

Height of tank in m

Deflection comparisons for tank model-3

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

Height of tank in m

Stress comparisons for tank model-1

Comparison for orientation of stiffeners

Outside Inside

45 40 Stress in MPa

35 30 25 20 15 10 5 0 0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

Height of tank in mm

Stress comparisons for tank model-1

SUMMARY & CONCLUSION •

• • •

Analysis of underground tank with two different geometries is carried out using Sensitivity approach. Vertical and horizontal cylindrical shapes have been investigated. Two different capacities of tanks are 5000 liters and 3000 liters have been investigated. For initial study simple cylindrical shape is selected, with the spherical dome shape in the top portion.

• In case of tank type-1, model-1 with minimum number of ribs, higher values of deflection at top portion have been obtained. This deflection reduces in the bottom region; • It is observed that in top portion of tank stresses increase beyond yield stress and it may fail due to higher deflection. • To investigate effect of stiffeners, radial stiffeners are introduced in top portion.

Model-1

Displacement contours

• For model-1 value of stresses are also high in some regions.( Von misses stress is consider for study of all affect.) • Von-stress is found more than 200 N/mm2 for this proposed typical geometry by Sintex industries. • Permissible value for LLDPE is 20 N/mm2

• •

• •

Model-2 is prepared with more stiffeners in tank wall But top part is retained same as model1. In this case deflection is again found higher, Overall deflection is reducing in comparison to model-1. In this case, it is noticed that due to more stiffeners, stress is reduced .

Stress reduction Von misses stresses in model-1

160

Von misses stresses in model-2

Stresses in Mpa

140 120 100 80 60 40 20 0 0

0.5

1

1.5

2

2.5

3

Height of tank in m

Stress comparison Tank type-1, model-2

Shape of stiffeners 93.9 N/mm2

Type-1

82.2 N/mm2

Von misses stress

Type-2

Tank type-2 • These tanks are horizontal cylindrical shape. • Three models are prepared for this type of underground tank. • For model-1 deflection and stresses are higher. • For model-1 stresses are crossing permissible limits of LLDPE and HDPE materials. • Model-2 is analyze with more stiffeners. • Model-2 with LLDPE is found to have higher stress but it is safe for HDPE material with 6mm thickness.

• Now for techno-commercial aspects, FRP material was introduce after detailed discussions with Sintex industries for model-1 • It is observed that deflection and stresses are reduced due to the reason that FRP has higher strength to weight ratio than LLDPE and HDPE • Deflection is 2mm for FRP material with only 4mm thickness. And highest stress is 9N/mm2 This investigation reveals that there are two tanks, which can be safe against given set of loadings by Sintex. • Now efforts are made to propose a tank design from techno-commercial aspects.

Techno-commercial aspect 160 140 Weight (Kg)

120 100 80 60 40 20 0

4

5

6

Model-1

69.25

86.9

103.23

Model-2

75.05

93.84

111.5

Model-3

90.68

113.35

136.03

Thickness of tanks (mm)

Weight comparison for tank type-2

•Now considering safe designs for weight comparison.

Design process

• • •

Model-1

Model-2

Weight- 69.25 Kg

Weight- 137.5 Kg

With FRP material Thickness 4 mm Minimum stiffeners

• • •

With HDPE material Thickness 6 mm More stiffeners

Tank with FRP material is best suited as underground storage tank

Future scope of work • For future work, it is possible to design multipurpose tanks, which can be used as underground storage tank as well transportable mobile tanks. • These investigations may include sloshing analysis of tank for transportable versions of Sintex industries. It is possible to produce more economical geometry by considering structural and practical aspects of tanks.

THANK YOU

Courtesy thanks to : M/s Sintex Industries Kalol for Sharing their Commercial drawings for Analysis work purely from academic point of view….