Seismic performance of circular elevated water tank with framed staging

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.1
Prof. Mangulkar Madhuri N.2
1
P. G. Student, Dept. of Structural Engineering, Jawaharlal Nehru Engineering College,
Aurangabad – 431003, Maharashtra, India.
2
Asst,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 earthquake
provided illustration when a great many water tank staging’s 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. INTRODUCTION
Water 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
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160
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 particular
region.
1.1 Lateral Stiffness Ks of 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=
ଵଶ ா௖ ூ௖ ே௖
௛ଷ
ቈ
ቀ
ಶ್಺್
ಽ
ቁ
ቀ
ಶ್಺್
ಽ
ቁାଶ‫כ‬ቀ
ಶ೎಺೎
೓
ቁ
቉For Intermediate panels, and ……. (1)
Kpanel=
௛ଷ
ቈ
ቀ
ಶ್಺್
ಽ
ቁ
ቀ
ಶ್಺್
ಽ
ቁାଵ‫כ‬ቀ
ಶ೎಺೎
೓
ቁ
቉For Top & Bottom panels.…….. (2)
Lateral Stiffness of Staging Ks-
Ks =
ଵ
∑ ቀ
భ
಼೛ೌ೙೐೗
ቁ
ಿ೛
೔సభ
. ……….. (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 Ks is calculated as below –
ଵ
௄௦
=
ଵ
௄௙௟௘௫௨௥௘
൅
ଵ
௄௔௫௜௔௟
Where ………. (4)
ଵ
௄௙௟௘௫௨௥௘
= ∑ ቀ
ଵ
௄௣௔௡௘௟
ቁே௣
௜ୀଵ
Kpanel=
௛ଷ
ቈ
ቀ
಺್
ಽ
ቁ
ቀ
಺್
ಽ
ቁାଶ‫כ‬ቀ
಺೎
೓
ቁ
቉ For Intermediate panel …… (5)
Kpanel=
௛ଷ
ቈ
ቀ
಺್
ಽ
ቁ
ቀ
಺್
ಽ
ቁାଵ‫כ‬ቀ
಺೎
೓
ቁ
቉ For Topmost and bottommost panel …. (6)

161
Kaxial =
ଶ
ே௖ ஺௖ ா ோଶ
∑ ‫2݅ܪ‬ ݄݅ே௣
௜ୀଵ ……… (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 STUDY
1. Numerical Problem Statement
A RC circular water container of 200 m3
capacity 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 IS
13920. 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.

162
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

163
1.4 Change in Iteration with respect to volume:
Table 3: Table showing change in iterations with respective to volume
Sr, No. Iterations
Volume 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 METHOD
Iteration 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
0
5000
10000
15000
20000
25000
30000
1 2 3 4 5
LateralStiffness
Iteration No
Comparison of Lateral Stiffness
Rapid- S. Jain STAAD Pro
75
175
275
375
1 2 3 4 5
BaseShear
Iteration No
Comparison of Base Shear for Static full condition-
Rapid- S. Jain STAAD Pro.

164
Static Empty condition
Hydrodynamic Full condition
Graph No 05: Comparison of Base Shear obtained by Software &Theoretical Method for
Hydrodynamic Empty condition
50
150
250
1 2 3 4 5
BaseShear
Iteration No
Comparison of Base Shear for Hydrodynamic Empty
condition
Rapid S. Jain STAAD Pro.
50
100
150
200
250
1 2 3 4 5
BaseShear
Iteration No
Comparison of Base Shear for Static Empty condition
150
200
250
300
1 2 3 4 5
BaseShear
Iteration No
Comparison of Base Shear for Hydrodynamic Full
condition

165
Graph No 06: Comparison of Base Moment obtained by Software & Theoretical Method for
Hydrostatic full condition
Hydrostatic Empty condition
Hydrodynamic Full condition
2000
3000
4000
5000
1 2 3 4 5
BaseMoment
Iteration No
Comparison of Base Moment for Hydrodynamic Full
condition-
Rapid- S. Jain STAAD Pro
2500
3500
4500
5500
1 2 3 4 5
BaseMoment-
Iteration No
Comparison of Base Moment for Hydrodstatic Full
condition-
Rapid S. Jain STAAD Pro.
2000
2500
3000
3500
1 2 3 4 5
BaseMoment
Iteration No.
Comparison of Base Moment for Hydrostatic Empty
condition-

166
Hydrodynamic Empty condition
Graph No. 10: Comparison of Total Hydrodynamic Pressure by Software & Theoretical
Method for Hydrodynamic Analysis of Elevated Water Tank
IV. CONCLUDING REMARKS
From 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 Ks obtained 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 Ks and same is used for Analysis &
design we will get the over stabilized or say over reinforced section, but it will be
uneconomical. Hence Ks by 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
0
1
2
3
4
5
6
1 2 3 4 5
HydrodynamicPressure-
Iteration No
Comparison of Hydrodynamic Pressure-
2600
2800
3000
3200
3400
1 2 3 4 5
BaseMoment-
Iteration No
Comparison of Base Moment for Hydrodynamic
Empty condition-

167
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. That’s 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. ACKNOWLEDGEMENTS
I 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 staging’s, 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.

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