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International Journal of Modern Trends in Engineering

e-

@IJMTER-2015, All rights Reserved

Response of Elevated Water Tank Subjected To

Field Earthquake Motion

1Applied Mechanics Department, L. D. College of engineering,

2Assistant professor Applied Mechanics Department, L. D. College of engineering,

Abstract - Elevated water tanks are life line structures for society and therefore it is must that

they remain functional after earthquake, so water is available for drinking and fire protection

purpose. Geometry of these tanks is such that large mass is concentrated at the top and that

increases the seismic vulnerability of these

vicinity of the earthquake epicenter probability of high damage or col

due to the effect of near-fault ground motions which differs from the usual far

motions in seismic characteristics. This paper attempts to study the behavior of Elevated

water tank subjected to near-fault and far fi

seismic response regarding the same. For this purpose elevated water tanks of four different

staging heights 12 m, 16 m, 20 m and 24 m with frame and shaft type staging profile are

modelled and simulated to near

STAAD.pro. Seismic response of these structures in terms of base shear, base moment and

displacement are obtained by performing time

that, tanks subjected to near fault earthquake show higher seismic response than tanks

subjected to far-field earthquakes.

Keywords-Elevated water tank; Staging pattern; Near

Elevated water tanks (EWT) are said to be life line structures for society as they facilitate

water supply with constant flow. It is very important that EWT remain functional after the

hazards like earthquakes as they satisfy the water demand for drinking

protection in emergency situations. From earthquake point of view elevated water tanks are

more susceptible to damage because of high mass concentration at top. Thus performance of

elevated water tank during earthquake has been subject of i

In past many studies have been carried out on the response of elevated water tanks subjected

earthquakes. Constant efforts are being made to improve the performance of water tank

earthquakes. Nevertheless many water tanks are being severely damaged and collapse

earthquakes. D. C. Rai [1] and Chirag N. Patel [2] have reported the failure

various frame and shaft supported water tanks during Indian ear

failure of shaft supported 265 kL water tank located at chobari village.

located about 20km from the epicentre. This exhibits that structures

vicinity suffer higher damage even if they

provision prescribed for that zone area, because near fault ground motion


and Research www.ijmter.com

-ISSN No.:2349-9745, Date: 2-4 July, 2015

rights Reserved

Response of Elevated Water Tank Subjected To Near-Fault And Far

Field Earthquake Motion

Shailja Upadhyay1, Chirag N. Patel

2

Applied Mechanics Department, L. D. College of engineering, Ahmedabad, India

Email: [email protected] Assistant professor Applied Mechanics Department, L. D. College of engineering,

Ahmedabad, India

Email: [email protected]

Elevated water tanks are life line structures for society and therefore it is must that



seismic vulnerability of these structure. Especially if the tank is in near

vicinity of the earthquake epicenter probability of high damage or collapse is very high. This

fault ground motions which differs from the usual far


fault and far field earthquake, and evaluate the differences in the



to near-fault and far-field ground motion using structural software


displacement are obtained by performing time-history analysis. It is observed by this study

nks subjected to near fault earthquake show higher seismic response than tanks

field earthquakes.

Elevated water tank; Staging pattern; Near-fault; Far-field; Time-history analysis

I. INTRODUCTION



hazards like earthquakes as they satisfy the water demand for drinking



elevated water tank during earthquake has been subject of interest for many researchers.

In past many studies have been carried out on the response of elevated water tanks subjected

earthquakes. Constant efforts are being made to improve the performance of water tank

earthquakes. Nevertheless many water tanks are being severely damaged and collapse

earthquakes. D. C. Rai [1] and Chirag N. Patel [2] have reported the failure

various frame and shaft supported water tanks during Indian earthquakes. Figure 1 shows the

failure of shaft supported 265 kL water tank located at chobari village. Cho

located about 20km from the epicentre. This exhibits that structures located in the nearby

vicinity suffer higher damage even if they are designed and detailed according to codal

provision prescribed for that zone area, because near fault ground motion differs in seismic


600

Fault And Far-

Ahmedabad, India

Assistant professor Applied Mechanics Department, L. D. College of engineering,

Elevated water tanks are life line structures for society and therefore it is must that



structure. Especially if the tank is in near-by

lapse is very high. This is

fault ground motions which differs from the usual far-field ground


eld earthquake, and evaluate the differences in the



field ground motion using structural software


history analysis. It is observed by this study

nks subjected to near fault earthquake show higher seismic response than tanks

history analysis



hazards like earthquakes as they satisfy the water demand for drinking as well as fire



nterest for many researchers.

In past many studies have been carried out on the response of elevated water tanks subjected to

earthquakes. Constant efforts are being made to improve the performance of water tank during

earthquakes. Nevertheless many water tanks are being severely damaged and collapse during the

earthquakes. D. C. Rai [1] and Chirag N. Patel [2] have reported the failure occurrences of

Figure 1 shows the

Cho-bari village is

located in the nearby

according to codal

differs in seismic

International Journal of Modern Trends in Engineering and Research (IJMTER)

Volume 2, Issue 7, [July-2015] Special Issue of ICRTET’2015

@IJMTER-2015, All rights Reserved 601

characteristics then regular far field one

.

Figure 1. Failure of shaft and frame supported water tank during Bhuj earthquake 2001, (Rai 2003)

Efforts are made by many engineers and researchers to study the characteristics of near-fault

earthquake and its effects on various structures. Maniatakis[4], Mavroeidis[5] and Pavel [6] have

studied the characteristics of near-fault ground motion and gave methods to represent them as

equivalent pulses. Tehrani and Najafi [7], tavakoli and naeej [8] and Dora foti [9] studied the

effects of near fault earthquakes on building and concluded that for the buildings subjected to near

fault earthquake there is increase in base shear, inter storey drift and ductility demand. Saha,

Matsagar and Jain [10] studied the effect of near fault earthquake on ground water tank with base

isolators. But little study has been made on the effects of near fault earthquake on elevated

waters tank. Talking about Indian subcontinent 59% of its geographical area is vulnerable to

seismic disturbance of varying intensities including the capital city of the country. Figure 2

shows seismic zone map and fault map of India. s per Geological Survey of India (GSI), about 67

active faults of regional extent exist in the country. Many of them pass from important and urban

areas which are highly populated. So it is very important to study the effect of near fault

earthquake on elevated water tank. This paper aims to study the seismic behavior of elevated

water tank with different staging configuration subjected to near fault earthquake.




Figure 2. seismic zones of India as per IS 1893 and active fault map provided by GSI

II. NEAR-FAULT AND FAR-FIELD EARTHQUAKE

Recent earthquakes in Northridge (1994); Kobe(1995); Kocaeli, Turkey (1999); and Chi-Chi,

Taiwan (1999) had caused vulnerable effects to the structures and human lives. These all

earthquakes had epicentre nearby the well-developed urban area and that increased the

severity of the damage. The people of the nearby areas were the most affected victims in all

the cases. Researchers have noticed that the near-field ground motions are quite different

from the usual far-field ones. On the contrary, the seismic codes deal with problems and

design procedures related to far-field or intermediate epicentral distances. And hence in cases

of near fault earth-quakes, damage arose also when both design and detailing have been

performed in perfect accordance with the code provisions [9].

According to Mohraz [4] if the distance between site and fault is less than 20 km it can be

said Near-fault earthquake. Near-fault ground motions have high peak ground acceleration

and velocity when compared to usual far-field records. Near fault ground motion have high




frequency change in short time duration and there-fore these records show a high magnitude

pulse in the beginning of velocity and acceleration time history. Teh-rani [4] showed the

existence of such pulse in his paper as shown in Figure 3. This kind of plus is also reflected in

the acceleration time history record of lomaprieta earthquake 1989. In this situation the

response of structure get from accumulation of waves move in structure. Increase in virtual

stiffness, base shear, ductility demand is also observed as the pulse effect, as the pulse sends

out the maximum domain of magnitude in very small pe-riod. Reduction in damping of the

structure is also an effect of pulse type ground motion only. In near fault ground motions

vertical component of acceleration is also high. Generally 2/3 is ratio of vertical to horizontal

spectrum for acceleration for far-field earthquake motion as prescribed by many codes. This

ratio becomes as high as 2 for near-fault ground motions.[4] Such increment in vertical

acceleration leads to increment of damage severity.

Fig. 3 Difference in near fault (Bam) earthquake and far field (Morgan) earthquake

Fig. 4 Near-fault and far field time history record, Loma Prieta 1989




III. DESCRIPTION OF STRUCTURE AND GROUND MOTION SIMULATION

In this study, models of Intz shape tank with 5 lac litters storage capacity have been investigated. Variations are made in tanks’ staging, both in height and pattern. Adapted

staging heights are 12 m, 16 m, 20 m and 24 m and for each height two staging pattern, frame

and shaft are taken under consideration. All the structures are made of RCC and grade of

concrete is M25. Tanks are designed with perfect accordance to the Indian Standard criteria

for liquid retaining structure located in seismic zone IV. Other structural configurations are as

per Table 1. Figure 5 shows the finite element models of the tanks prepared in STTAD-pro.

Table No. 1. Configuration of tank container

Sr. No. Component Frame Staging Shaft Staging

1 Diameter of container (m) 10.4 13.3

2 Diameter of bottom dome (m) 7.280 10.77

3 Thickness of bottom dome (mm) 150 120

4 Height of conical dome (m) 2.080 2.13

5 Thickness of conical dome (mm) 350 280

6 Height of cylindrical wall (m) 6.240 3.35

7 Thickness of cylindrical wall (mm) 200 140

8 Thickness of top dome (m) 120 100

9 Dimensions of top ring beam (mmxmm) 300x300 300x300

10 Dimensions of middle ring beam (mmxmm) 350x450 400x500

11 Dimensions of bottom ring beam (mmxmm) 500x750 150x300

Fig. 5 STAAD-pro model for frame and shaft supported tanks

To study the effect of near-fault earthquake on elevated water tank, here Kobe earthquake

1995 is taken into consideration. The January 17, 1995 Hyogoken-Nanbu earthquake of

magnitude 7.2 in JMA scale (Mw = 6.9), which struck Kobe, Japan. Fault rupture length was

about 60 km. Near-fault and far field data for this earthquake are simulated in STAAD-pro

for time history analysis. The near-fault data was recorded at Nishi-Akashi station, having the

epicentral distance of 8.7 km with PGA value of 0.486 (g) and far-field data as recorded at

Kakogawa station, having epicentral distance of 24.2 km with PGA value of 0.266(g). Other




seismic parameters are listed in table 2. Acceleration time history for this earthquake

recorded at both stations is obtained from PEER NGA data base. Time history plots for both

stations are shown in figure 6 which shows the difference in acceleration values and also the

existence of pulse in beginning of record.

Table No. 2. Ground motion data for Kobe earthquake (1995)

Station

Seismic parameters

Epicentral

Distance (km)

Hypocentral

Distance (km)

PGA

(g)

PGV

(cm/sec)

PGD

(cm)

Nishi-Akashi 8.70 19.90 0.4862 35.7300 10.7500

Kakogawa 24.20 30.10 km 0.2668 21.6600 7.6000

Fig. 6 Time history plot for Kobe earthquake for near-fault and far field data

IV. RESULT AND CONCLUSION

The seismic behavior of elevated water tank is studied here in the terms of base shear, base

moment and displacement at different height levels. By studying the variations in these

parameters for near-fault and far field earthquake suitability of tanks in different regions can

be decided. Results for different staging height and staging patterns can suggest the favorable

staging configuration.

4.1 Base shear and Base moment

For all the water tanks considered here base shear value for time history analysis is high in

case of near-fault earthquake than far-field earthquake. Figure 4 shows the base shear values

for frame and shaft supported water tank of different staging height. Graph indicates that base




Fig 7.1 Base shear for frame and shaft type staging for different staging height subjected to near-fault

and far field earthquake.

Fig 7.2 Base moment for frame and shaft staging for different staging height subjected to near-fault

and

far field earthquake.

shear value is high for near fault earthquake. But for different staging height it changes non-

uniformly. For shaft supported tank base shear increases with increasing height. Tanks

subjected to Near-fault ground motions experience high base moments as compared to far

field ground motion. This can be seen from figure 7 which exhibits the results of base

moments for frame and shaft type staging of different heights. It is also seen that base

moment in case of shaft supported tank increases with increase in staging height

4.2 Displacements at various height levels of water tank

By comparing the results of displacement at various bracing level for both frame and shaft

supported water tank, it is observed that tanks subjected to near fault earthquakes experience

higher displacement at each level as compared to far field earthquake. Figure 8.1 and figure

8.2 shows the displacement in horizontal x direction at different bracing levels for frame and




shaft staging respectively. The solid lines represent the results for far-field earthquake motion

while the dashed lines represent the results for near-fault earthquake motion. Increase in

displacements is also observed with increment in height of staging.

Fig 8.1 Horizontal displacement of frame type staging EWT for different staging height subjected to

near-

fault and far field earthquake.

Fig 8.2 Horizontal displacement of shat type staging EWT for different staging height subjected to

near- fault and far field earthquake.




V. CONCLUSION

� It is clear from the results that seismic response of water tank is higher for near fault

ground motion than far field earthquake. Variation in staging type and height are

adapted to study the effect of them on response. Certain conclusions can be made by

the time history analysis of tanks.

� For water tank with frame type of staging base shear is always high for near fault

earthquake than far field earthquake, but this variation in base shears increases with

increasing staging height. For 16 m staging height only 6.4% increment is observed

which goes up to 13.8 % and 12.3% for 20 m and 24 m staging height respectively.

� For water tank with shaft type staging base shear is higher for any ground motion than,

observed base shear in frame type staging. Here also base shear variation increases

with increment in height. for 16 m staging height base shear for near fault ground

motion is about 7.19 % higher than base shear for far field ground motion. But this

variation increases up to 31% and 62.63% for 20 m and 24 m staging heights

respectively.

� Base moment is also increased for near fault ground motion for all the cases. This

increment is quite same as increment in base shear for all height variation for both

frame and shaft type staging.

� From studying the displacement values at different heights it is observed that

horizontal displacement is higher for frame staging supported water tank than tank

with shaft type staging. Say for 24 m staging height displacement of top crown of

container is about 73% higher for frame staging than shaft staging when subjected to

near fault earthquake.

� With increasing staging height variation of horizontal displacement also increase. For

near fault ground motion displacement of top crown node in x direction is about 2.41%

higher than far field ground motion, which increases up to 37.19% and 67.66% in case

of 20 m and 24 m staging height. Shaft type staging shows the similar observation. For

16 m staging height variation is about 6.32% which increases up to 14.73% and

21.14% for 20 m and 24 m staging height.

� It can be concluded from the results that 16 m is the staging height for which variations

are very less in any parameter for both the staging type.




REFERENCES

1. Durgesh C Rai, Performance of elevated tanks in Mw 7.7 Bhuj earthquake of January 26th,

2001. Indian Acad. Sci. (Earth Planet. Sci.), 112, No. 3, pp. 421-429, (2003

2. Chirag N. Patel and H. S. Patel, Former failure assessments of RC elevated water tanks:

literature review, GIT-Journal of Engineering and Technology – 2012. [ISSN- 2249-6157],

2012

3. Chirag N. Patel and H. S. Patel, Supporting system for reinforced concrete elevated tanks: a

state of the art literature review, International journal of Advanced Engineering

Resource and Studies (IJAERS), [ISSN 2249-8974], Vol 2, Issue-1 pp. 68-71, 2012

4. Ch.A. Maniatakis, I.M. Taflampas and C.C. Spyrakos, Identification of near-fault

earthquake record characteristics, World Conference on Earthquake Engineering, China,

2008

5. G. P. Marvroeidis, A.S Papageorigion, Near-fault ground motion and its relation to the fault

rupture process, 14WCEE

6. F. Pavel, A. Aldea, R vacareanu, Near-field strong ground motion records from Vrancea

earthquakes

7. Tehrani Zade.M, Haj Najafi.L, Assessing seismic behavior of eccentrically braced frames

(ebfs) due to near-field ground motions. The 14th World Conference on Earthquake

Engineering, china, 2008

8. Tavakoli.H.R, Naeej.M, Salari.A, Response of RC structures subjected to near-fault and far-

fault earthquake motions considering soil-structure interaction, international journal of civil

and structural engineering Volume 1, No 4, 2011

9. Dora Foti, On the Seismic Response of Protected and Unprotected Middle-Rise Steel Frames in

Far-Field and Near-Field Areas, Hindawi Publishing Corporation Shock and Vibration. Volume

2014, Article ID 393870, 11 pages, 2014

10. S. K. Saha, V.A. Matsagar and A.K. Jain, Response of base-isolated liquid storage tanks

under near-fault earthquakes, ISET golden jubilee symposium, Indian society of earthquake

technology department of earthquake engineering building, IIT roorkee, Paper No. D011,

2012

11. IITK-GSDMA guidelines (2007), “Seismic design of liquid storage tanks, provisions

with commentary and explanatory examples”.

12. I.S 1893:1984, “Criteria for earthquake resistant design of structures”, Bureau of

Indian Standards, New Delhi.

13. I.S 1893:2002, “Criteria for earthquake resistant design of structures”, Bureau of

Indian Standards, New Delhi.

14. IS 3370 (Part II) : 2009, “Code of practice for concrete structures for the storage of

liquids part II reinforced concrete structures”, Bureau of Indian Standards, New Delhi.

15. IS 456:2000, “Plain and Reinforced Concrete, Code of Practice”, Bureau of Indian

Standards, New Delhi.

16. Preliminary Draft code IS 11682:1985, “Criteria for Design of RCC Staging for

Overhead Water Tanks”, Bureau of Indian Standards, New Delhi, June 2011.

17. www.portal.gsi.gov.in

18. Pacific Earthquake Engineering Research Center, (2011), User’s Manual For The



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