WIND ANALYSIS OF ELEVATED WATER TANK FOR DIFFERENT …

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WIND ANALYSIS OF ELEVATED WATER TANK FOR DIFFERENT

BRACING SYSTEM

Ms. Susmitha S.K*1, Mr. Pradeep Karanth*2 *1M.Tech Structural Engineering, Department Of Civil Engineering, NMAM Institute

Of Technology, Nitte. India.

*2Assistant Professor, Department Of Civil Engineering, NMAM Institute

Of Technology, Nitte. India.

ABSTRACT

Elevated water tanks, are critical structures that must be capable of maintaining expected performance, i.e.

functioning during and after strong winds. Analysis of a hydrodynamic construction such as elevated concrete

water tank is particularly difficult. That may be because of a lack of understanding of right behaviour of the

tank's supporting system due to the dynamic effect, as well as improper geometrical staging selection. The

primary goal of this research is to better understand the behaviour of various staging systems under various

loading condition, as well as to improve the traditional staging system to provide better performance during

high winds. STAAD Pro is used to do equivalent static analysis for several forms of bracings system, which is

then used to the staging of an elevated intze water tanks. The base shears and displacements of the water tank

in X, Y, and Z directions are compared for empty, half-filled, and full conditions. After calculation of base shears,

nodal displacements, and buckling of columns for empty, half full, and full containers using various types of

bracing systems in staging, the project study will recommend the types of bracings that give the least base

shears and the most displacement for measuring wind zones.

Keywords: Elevated Intze Tank ,Wind Analysis, Base Shear, Nodal Displacement, Wind Zones.

I. INTRODUCTION

Water is an essential necessity for daily existence, and its distribution is determined by the construction of a

water tanks in a particular location. Supply of water is lifeline which should stay operational in the event of a

calamity. An elevated water tank is a water tank that is constructed to deliver water at a height high enough to

pressurise a water distribution system. Institutions and industrial estates have their very own supply networks

include elevated tanks, supplement the main supply plan in major cities. During the hurricane, the storage

tanks were also shifted by a few metres and some were flipped due to the wind.

The wind picked them up and carried them away. When flying debris collided with the tanks, it left dents on the

surfaces. As a result, it's critical to assess the severity of these forces in a given place. Reinforced concrete

raised water tanks are damaged or fail of modest to higher capacities was discovered through the examination

of damage histories. Even after a disaster, damage to critical lifeline facilities such as elevated water tanks can

cause substantial challenges, resulting in human deaths and economic losses to the built environment. The

study of wind's effects has been acknowledged as an essential step in understanding natural hazards and their

long-term risk to society.

A water towers can be used as a reservoirs to meet water demands during optimum periods. Elevated building

that supports a water tanks that is tall enough to pressurise water supplies systems for delivery of water as

well as provides immediate storages for fire safety. People use word "stand pipe" to address to a water towers,

particularly with high and fine proportion. Water tower can provide water still in the event of a power outage

since they depend on hydrostatic pressures (caused with gravity) to force water into home and industrial water

distribution systems.

a) Classification of water tanks based on shape

1) Circular tanks

2) Rectangular tanks

3) Spherical tanks





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4) Intze tanks and

5) Circular tanks with conical bottoms

b) Intze Tanks

The Intze principles is used to a types of water towers in one example and kind of dam in the other.Circular

tanks with a flat bottom and a domical bottom are available.The thickness and strengthening of the flat bottom

are determined to be substantial. Though the dome's thickness and reinforcement are normal, the ring beam's

reinforcement is excessive. As a result, in the case of big diameter tanks, a cost-effective solution would be to

use a conical dome to minimise the diameter at the bottom. The Intze tank is a type of tank that is fairly

widespread. The fundamental advantages of the Intze tanks is that the conical bottom's in-ward radial thrusts

balances the spherical bottom out-ward radial thrusts.

General Layout Of Intze Tank

c) Wind Load

While analyzing the stresses the combination shall be as follows.

1) Wind load with empty tank

2) Wind load with tank half full tank and

3) Wind load with full tank.

d) Objectives

1) To determine the base shear, buckling of columns, roof displacement for wind loads with different

boundary condition for different bracing system.

2) To determine the base shear, buckling of columns, roof displacement for wind loads with different zone

condition for different bracing system.

3) To analyse and conclude the better bracing system for intze elevated tank.

II. METHODOLOGY

In this project elevated intze tank is considered and normal cross and radial bracing system is applied by

considering the full half and empty tank conditions. Analysis is made for roof displacement and buckling for the

above tank conditions for wind velocity of 47m/s and 55 m/s and they are compared to know which bracing

system gives the best result in terms of roof displacement and buckling. The methodology is represented below

in terms of a flow chart.





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Figure:1 Flow Chart Of Methodology

Initially an intze water tank is designed and modelled in the STAAD PRO. Manual data such as wind intensity

and water pressure is calculated. With the given data we finally design the model in STAAD PRO for empty, half

and full water condition.This is designed to every bracing systems such as normal, cross and radial. Roof

displacement, buckling of columns, base shear is noted down.

a) Description of Intze Elevated Water Tank

For the analysis purpose intze tank is considered of tank capacity 1000m3 of diameter 14m and of staging 12m.

Other parameters and its value is given in the table below. The bracing system such as normal, cross and radial

is considered and their dimensions are given below.

Table 1: Details of intze Elevated RC Water Tank

SL.NO PARAMETERS VALUES

1. CAPACITY (m3) 1000

2. DIAMETER (m) 14

3. HEIGHT OF CYLINDRICAL WALL(m) 5.5

4. THICKNESS OF CYLINDRICAL WALL(mm ) 275

5. HEIGHT OF STAGING(m) 12

6. NO. OF COLUMNS 8





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7. DIAMETER OF COLUMNS(mm) 700

8. SIZE OF BEAM BXD (mm)

• TOP RING BEAM 400x300

• BOTTOM RING BEAM 1200X600

9. BOTTOM RING GIRDER(mm) 600x1200

10. BRACING SIZE (mm)

• Normal

• Cross

• Radial

300x600

300x300

300x300

11. DENSITY OF CONCRETE (KN/m3) 25

b) Manual calculation

Design wind speeds of (Vz) at some height is

Vz = Vb k₁ k₂ k₃ ……….[1]

Where, Vz = Design wind speeds at someheight ‘z’ in m/s

Vb = Basic wind speed for any site

k₁ = Probability factor (Risk coefficient)

k₂ = Terrain, height and structure size factor

k₃ = Topography factor

k₁, k₂ & k₃ are calculated by means of tables in IS 875 (Part-3) 2003.

The design wind pressures at some height is

here, Pz = Design Wind pressures in N/m² at height z,

Vz = Design wind velocities in m/s height z

In this project we are considering wind velocity as 47 m/s and 55m/s for category 2 .

1. For Vb=47m/s

Vz=47x1x1.09x1x1

=51.23 m/s

Pz=0.6x51.23x51.23

=1.5KN/m2

2. For Vb=55m/s

Vz=55x1x1.09x1x1

=59.95 m/s

Pz=0.6x59.95x59.95

=2.1 KN/m2

Self weight of bottom spherical dome = 2x xRxHxTx25………….[3]

Here R= radius of spherical dome

H= Central rise of dome

T= thickness of dome

Hence self weight =2x x5.52x2x0.25x25

=433.54KN

Weight of water = [(π/4)x8.52(5.5+2)-(π/3)x22(3x5.52-2)]x9.8





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=3573 KN

Total load = 3573+433.54=4006.54KN

Therefore ,

Water pressure =4006.54/(π(8.5/2)2)

=70.6KN/m2

III. MODELING AND ANALYSIS

By collecting the data from manual calculation we model the intze tank in STAAD PRO and accordingly the

model is obtained. Now as per calculations we are modelling the intze tank for normal cross and radial bracing

for 2 different wind velocity that is 47m/s and 55m/s. Along with this we are also considering the water

pressure 70.6 KN/m2 as full tank condition. 35.3KN/m2 for half tank condition and zero for empty tank

condition.

So respectively the models were prepared for intze tank with different zones and different boundary

conditions. So each model is made with bracing condition , zone condition and boundary condition. All the

manual data like wind intensity and water pressure are applied in STAAD PRO to get the wind zone condition as

well as the boundary conditions. The tank with all the other dimensions were created and the given specific

bracing system. Fig 2, fig 3, fig 4 shows the 3 D MODEL of the intze tank.

Figure:2 3D model of normal bracing

Figure:3 3D model of cross bracing

Figure:4 3D model of radial bracing





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Figure:5a Shear Bending Of Columns

Figure:5b Roof Displacement Of Top Node

IV. RESULTS AND DISCUSSION

The calculation of wind force is a critical parameter for raised water tanks, which are particularly vulnerable to

horizontal forces due to their huge mass concentration at a great height. The magnitude of the wind force

varied numerous factors, and the results were tabulated for 24 tanks.

By adding the appropriate Wind forces to the FEM model, the Roof displacements for tank empty, tank half, and

tank full situations are calculated. Table 2 shows the roof displacements for normal, radial, and cross bracing

systems in various tank filling conditions at varied Basic wind speeds in zone 4 and zone 5. In the tank, the roof

displacement The empty condition is higher than the half-full and half-full conditions, as can be observed.

Table 2: Roof Displacements Values





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Figure:6 Graph Of Roof Displacements

By applying the corresponding Wind forces to the FEM model, the base shear for tank empty, tank half, and tank

full situations is obtained. Table 3 shows the Base shear for normal, radial, and cross bracing systems in various

tank filling conditions. The Base shear in the tank empty state is larger than the tank half and full condition.

Table 3: Base Shear Values

Figure:7 graph of base shear

The buckling of the column of elevated tank is examined and we are observing that buckling of column is more

in empty tank rather than half and full. The buckling value is lesser with full tank conditions than the other tank

condition as well as the values increasing with increase in wind velocity. This can be observed in the table 4.





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Table 4: buckling values

Figure:8 Graph Of Buckling

V. CONCLUSION

• Base shears, Buckling of columns, Roof displacements values are compared.

• These values are more for empty tank conditions than for half full and full tank conditions and they increase

with increase in wind velocity.

• When compared its observed that radial bracing system is much more safer than any normal and cross

bracing system.

• Full tank condition is always safer when compared to half and empty conditions.

VI. REFERENCES

[1] Luis A. Godoy, Fernando G. Flores(1998) “Buckling of short tanks due to hurricanes” Civil Engineering

Department, University of Puerto Rico at Mayaguez, Mayaguez, PR 00681-5000, USA.

[2] Zhao et.al.(2013) “Design of large circular steel silos subject to wind pressure”, Space Structures

Research Center, Zhejiang University, Hangzhou, China.

[3] Yang Zhaon & Yin Lin(2014) “Buckling of cylindrical open-topped steel tanks under wind load” Spatial

Structures Research Center, Zhejiang University, Hangzhou 310058, China.

[4] Uematsua et.al.(2015) “Design wind loads for open-topped storage tanks in various arrangements”

Department of Architecture and Building Science, Tohoku University, Sendai, Japan.





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[5] A R. Shokrzadeh & M R. Sohrabi(2016)“Buckling of ground based steel tanks subjected to wind and

vacuum pressures considering uniform internal and external corrosion” Department of Civil

Engineering, University of Sistan and Baluchestan, Zahedan, Sistan and Baluchestan, Iran.

[6] L A Godoy (2016)“Buckling of vertical oil storage steel tanks: Review of static buckling studies” science

and Technology Research Council (CONICET), Argentina.

[7] Y.C Chiang & S.Guzey(2019) “Dynamic analysis of above ground open-top steel tanks subjected to wind

loading”, Lyles School of Civil Engineering ,PurdueUniversity, WestLafayette,USA.

[8] Jumpei Yasunaga & Yasushi Uematsu(2020)” Dynamic buckling of cylindrical storage tanks under

fluctuating wind loading” Steel Research Laboratory, JFE Steel Corporation, Kawasaki, Japan.

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WIND ANALYSIS OF ELEVATED WATER TANK FOR DIFFERENT …