seismicperformanceofcircularelevatedwatertank

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International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN

0976 6480(Print), ISSN 0976 6499(Online) Volume 4, Issue 4, May June (2013), IAEME

159

SEISMIC PERFORMANCE OF CIRCULAR ELEVATED WATER

TANK WITH FRAMED STAGING SYSTEM

Gaikwad Madhukar V.1Prof. Mangulkar Madhuri N.

2

1P. G. Student, Dept. of Structural Engineering, Jawaharlal Nehru Engineering College,

Aurangabad 431003, Maharashtra, India.2Asst,Professor, Dept. of Structural Engineering, Jawaharlal Nehru Engineering College,

Aurangabad -431003, Maharashtra, India.

ABSTRACT

Water tank is used extensively for storage water, inflammable liquids, and other

chemicals. The current analysis and design of supporting structures of elevated water tanks

are extremely vulnerable under lateral forces due to an earthquake and the Bhuj earthquakeprovided illustration when a great many water tank stagings suffered damage and a few

collapses. The aim of this paper is to understand the behavior of Elevated Water Tank with

the framed staging in lateral earthquake loading using IITK-GSDMA Guidelines by

considering two theoretical theories given by Sudhir Jain &Sameer U. S. [1990] and Rapid

Assessment of Seismic Safety of Elevated Water Tank with framed staging & Software

STAAD Pro.-2007,for calculate the lateral stiffness. Same values of lateral stiffness Ks is

used for further analysis. After details study it was found that the lateral stiffness Ksobtained

by using Rapid Assessment of Seismic Safety of Elevated Water Tank gives the optimum

value of Base Shear and Base Moment and hence it is economical. The design based on

above gives the most economical section and also it is safe.

Keywords Elevated Water Tank, Lateral Stiffness, Seismic Analysis, STAAD. Pro 2007,

Rapid Assessment of Earthquake safety.

I. INTRODUCTIONWater supply is a life line facility that must remain functional following disaster.

Most municipalities in India have water supply system which depends on elevated water

tanks for storage. Elevated water tank is a large elevated water storage container constructed

INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN

ENGINEERING AND TECHNOLOGY (IJARET)

ISSN 0976 - 6480 (Print)ISSN 0976 - 6499 (Online)

Volume 4, Issue 4, May June 2013, pp. 159-167

IAEME: Journal Impact Factor (2013): 5.8376 (Calculated by GISI)

IJARET

I A E M E


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for the purpose of holding a water supply at a height sufficient to pressurize a water

distribution system. These structures have a configuration that is especially vulnerable to

horizontal forces like earthquake due to the large total mass concentrated at the top of slender

supporting structure. So it is important to check the severity of these forces for particularregion.

1.1 Lateral Stiffness Ksof frame staging:

1.1.1. By considering Rapid Assessment of Earthquake safety of Elevated Water Tank:

The design seismic forces for the water tank depends on its flexibility and hence on

the time period. Often, column stiffness is considered as 12EI/ L3, which is based on the

assumption that bracing beams are infinitely rigid. In practice, these beams are flexible and

therefore the assumption overestimates the staging stiffness.

Most tank staging have identical bracing girders and equal panel heights. Moreover,

the top end of column in topmost panel and bottom end of column in bottommost panel are

fixed against rotation. For the most commonly used staging, having all the columns along the

periphery of a circle, panel stiffness is obtained as below-

Kpanel=

For Intermediate panels, and . (1)

Kpanel=

For Top & Bottom panels... (2)Lateral Stiffness of Staging Ks-

Ks=

. .. (3)

When Tank structure is located on soft soil, the support is not rigid and hence

bottommost panel is no more fixed against rotation. Under these condition, the panel stiffness

is calculate using Eq. (1), which accounts for end rotations.

1.1.2. By considering Sudhir Jain &Sameer U.S. [1990]-

Sudhir Jain and Sameer has given simple expression to evaluate the lateral stiffness of

framed type supporting system by considering the effect of girder flexibility. For tank staging

with equal panel heights, identical columns arranged along the periphery of a circle, and

identical bracing girders, the lateral stiffness of the staging Ksis calculated as below

=

Where . (4)

= Kpanel=

For Intermediate panel (5)

Kpanel=

For Topmost and bottommost panel . (6)


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Kaxial=

(7)Where,

H = Height of Panel from CG of container.h = Height of panel.

1.1.3. By using STAAD. Pro 2007 Software

Lateral stiffness of staging is defined as the force required to be applied at the CG of

tank so as to get a corresponding unit deflection. From the deflection of CG of tank due to an

arbitrary lateral force one can get the stiffness of staging.STADD Pro software is used to

model the staging.

II. CASE STUDY1. Numerical Problem Statement

A RC circular water container of 200 m3capacity has internal diameter of 8.50 m and

height of 3.82 m (including freeboard of 0.3 m). It is supported on RC staging consisting of 6

columns of 550 mm dia. with horizontal bracings of 300 x 550 mm at four levels. The lowest

supply level is 12 m above ground level. Staging conforms to ductile detailing as per IS13920. Staging columns have isolated rectangular footings at a depth of 2m from ground

level. Tank is located on soft soil in seismic zone III. Grade of staging concrete and steel are

M20 and Fe415, respectively. Density of concrete is 25 KN/m3. Analyze the tank for seismic

loads.

Elevated water tank can be analyzed by both the condition i.e. for tank full condition

and tank partially filled condition.


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1.1 Preliminary Data

Table 1:Sizes of various components

Sr. No. Components Size (mm)1 Roof Slab 175 Thick

2 Wall 225 Thick

3 Floor Slab 225 Thick

4 Gallery 110 Thick

5 Floor Beams 300 *600

6 Braces 300 *550

7 No of Column 06

8 Dia. of Column 550

1.2 Formulation of Problem

Table 2:Constants which are considered for calculation

Sr. No. Constant Values Remarks

1 Z 0.16 Structure assumed in Zone III

2 I 1.5 Importance Factor

3 R 3.0 Response Reduction Factor

4 M-20 Grade of Concrete

5 Fe- 415 Grade of Steel

1.3 Details of Tank Geometry


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1.4 Change in Iteration with respect to volume:

Table 3:Table showing change in iterations with respective to volume

Sr, No. IterationsVolume in

Lit.

Diameter of

container in

meter

Height of

tank in

meter

Free Board

of Tank in

meter

01 1 200,000 8.50 3.82 0.30

02 2 8.00 4.28 0.30

03 3 7.50 4.90 0.30

04 4 7.00 5.50 0.30

05 5 6.50 6.40 0.30

III. ITERATION OF RESULTS BY GRAPHICAL METHODIteration of Results includes the graphical representation of output parameters which

are calculated as a solution.

Graph No 01:Comparison of Lateral Stiffness obtained by Software & Theoretical Method

Graph No 02:Comparison of Base Shear obtained by Software & Theoretical Method for

Static Full condition

LateralStiffness

Iteration No

Comparison of Lateral Stiffness

BaseShear

Iteration No

Comparison of Base Shear for Static full condition-


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Static Empty condition


Hydrodynamic Full condition

Graph No 05:Comparison of Base Shear obtained by Software &Theoretical Method for

Hydrodynamic Empty condition

BaseShear

Iteration No

Comparison of Base Shear for Hydrodynamic Empty

condition

BaseShear

Iteration No

Comparison of Base Shear for Static Empty condition

BaseShear

Iteration No

Comparison of Base Shear for Hydrodynamic Full

condition


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Graph No 06:Comparison of Base Moment obtained by Software & Theoretical Method for

Hydrostatic full condition


Hydrostatic Empty condition


Hydrodynamic Full condition

BaseMoment

Iteration No

Comparison of Base Moment for Hydrodynamic Full

condition-

BaseMoment-

Iteration No

Comparison of Base Moment for Hydrodstatic Full

condition-

BaseMoment

Iteration No.

Comparison of Base Moment for Hydrostatic Empty

condition-


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Hydrodynamic Empty condition

Graph No. 10:Comparison of Total Hydrodynamic Pressure by Software & Theoretical

Method for Hydrodynamic Analysis of Elevated Water Tank

IV. CONCLUDING REMARKSFrom above mentioned detailed study and analysis some of the conclusion can be

made as follow

Graph No 1 clearly shows the comparison of Lateral Stiffness obtained from three

different methods. If we observe the graph, the value of Ksobtained from Sudhir Jain and

STAAD Pro. is higher than the Rapid Assessment of seismic safety. If we analyze the

elevated water tank by considering the higher value of K sand same is used for Analysis &

design we will get the over stabilized or say over reinforced section, but it will be

uneconomical. Hence Ksby using Rapid Assessment of seismic safety is economical.

Graph No 2 to 5 shows the comparison of Base Shear for Tank Full and Empty

condition by using three different methods for Hydrostatic& Hydrodynamic Analysis of

Hy

drodynamicPressure-

Iteration No

Comparison of Hydrodynamic Pressure-

BaseMoment-

Iteration No

Comparison of Base Moment for Hydrodynamic

Empty condition-


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Elevated Water Tank. The values of Base Shear obtained from Tank full condition is greater

than the Tank Empty condition and hence considered for further analysis. If we observe the

graphs we find that the Base Shear obtained from Rapid Assessment of seismic safety is

lesser than the other two, and hence it is economical.Graph No. 6 To 9 shows the comparison of Base Moment for Tank full and Empty

condition by using three different methods for Hydrostatic & Hydrodynamic Analysis of

Elevated Water Tank. Base Moment obtained from Rapid Assessment of seismic safety is

lower than other two. If we design by considering the higher value we get over stabilized or

say over reinforced section. It is safe but uneconomical. Thats why Hydrostatics system of

designing of elevated water tank is not useful in seismic Zones. And hence, IS code provision

for static analysis is restricted for small capacities of tanks only. For Hydrodynamic analysis

the Base Moment obtainsfrom Rapid Assessment of seismic safety is lesser than the other

two, and hence it is economical.

Graph No 10 shows the comparison of Hydrodynamic pressure on wall as well as on

base of Elevated Water tank. Total hydrodynamic pressure obtained from Rapid Assessment

of seismic safety is lesser than the other two, and hence it is economical.From detail study and analysis, it was found that the analysis and design based on

Lateral Stiffness Ks obtained from Rapid Assessment of Earthquake safety of Elevated Water

Tanks with Frame Staging is most economical and safe.

V. ACKNOWLEDGEMENTSI wish to thank the Management, Principal, Head of Civil Engineering Department

and Staff of Jawaharlal Nehru Engineering College and authorities of Dr. Babasaheb

Ambedkar Marathwada University for their support.

REFERENCES

[1]. IITK-GSDMA Guidelines for Seismic Design of Liquid Storage Tanks Provision with

commentary and explanatory examples. NICEE, IIT Kanpur.

[2]. IS 1893-1984, Criteria for Earthquake Design of Structures, BIS, New Delhi.

[3]. IS 1893-2002 (Part-I) Criteria for Earthquake Resistant Design of Structure Part-1,

General Provisions and buildings, BIS, New Delhi.

[4]. Sudhir Jain & Sameer U. S [1990] , Approximate method for determination of Time

Period of Water Tank stagings, The Indian concrete journal, Vol-66, No-12

[5]. Rapid Assessment of Seismic Safety of Elevated Water Tanks with Frame Staging.

[6]. STAAD Pro. 2007, Structural analysis and design programing -2007 for analysis of

lateral stiffness.

[7]. Mangulkar Madhuri N. and Gaikwad Madhukar V., Review on Seismic Analysis of

Elevated Water Tank, International Journal of Civil Engineering & Technology (IJCIET),Volume 4, Issue 2, 2013, pp. 288 - 294, ISSN Print: 0976 6308, ISSN Online: 0976 6316.

[8]. Mangulkar Madhuri N. and Gaikwad Madhukar V, Comparison between Static and

Dynamic analysis of Elevated water Tank, International Journal of Civil Engineering &

Technology (IJCIET), Volume 4, Issue 3, 2013, pp. 12 - 29, ISSN Print: 0976 6308,

ISSN Online: 0976 6316.

seismicperformanceofcircularelevatedwatertank

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