Review on seismic analysis of elevated water tank 2


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Review on seismic analysis of elevated water tank 2

  1. 1. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 2, March - April (2013), © IAEME288REVIEW ON SEISMIC ANALYSIS OF ELEVATED WATER TANKMangulkar Madhuri. N.1,Gaikwad Madhukar V.21Asst. professor Dept. of Structural Engineering, J. N. E. C. Aurangabad (M. S), India2P. G. Student, Dept. of Structural Engineering, J.N.E.C.Aurangabad (M. S.), IndiaABSTRACTElevated Water Tanks are one of the most important lifeline structures in theearthquake regions. In major cities and also in rural areas elevated water tanks forms anintegral part of water supply scheme. The elevated water tanks must remain functional evenafter the earthquakes as water tanks are required to provide water for drinking andfirefighting purpose. These structures has large mass concentrated at the top of slendersupporting structure hence these structure are especially vulnerable to horizontal forces due toearthquakes. All over the word, the elevated water tanks were collapsed or heavily damagedduring the earthquakes because of unsuitable design of supporting system or wrong selectionof supporting system and underestimated demand or overestimated strength. So, it is veryimportant to select proper supporting system and also need to study the response of ElevatedWater Tanks to dynamic forces by both equivalent Static method as well as Dynamic methodand to find out the design parameters for seismic analysis. It is also necessary to consider thesloshing effect on container roof slab. This sloshing of water considerably differ theparametric values used in design and economy of construction. The effect of hydrodynamicpressure must be considered in the seismic analysis of Elevated Water Tank.Keywords – Elevated Water Tank, Seismic analysis.INTRODUCTIONIndian sub- continent is highly vulnerable to natural disasters like earthquake,draughts, floods, cyclones etc. Majority of states or union territories are prone to one ormultiple disasters. These natural calamities are causing many casualties and innumerableproperty loss every year. Earthquakes occupy first place in vulnerability. Hence, it isnecessary to learn to live with these events. According to seismic code IS: 1893(Part I): 2000,more than 60% of India is prone to earthquakes. After an earthquake, property loss can beINTERNATIONAL JOURNAL OF CIVIL ENGINEERING ANDTECHNOLOGY (IJCIET)ISSN 0976 – 6308 (Print)ISSN 0976 – 6316(Online)Volume 4, Issue 2, March - April (2013), pp. 288-294© IAEME: Impact Factor (2013): 5.3277 (Calculated by GISI)www.jifactor.comIJCIET© IAEME
  2. 2. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 2, March - April (2013), © IAEME289recovered to some extent however, the life loss cannot. The main resign for life loss iscollapse of structures. It is said that earthquake itself never kills people; it is badlyconstructed structures that kill. Hence it is important to analyze the structure properly forearthquake effects.Water supply is a life line facility that must remain functional following disaster. Mostmunicipalities in India have water supply system which depends on elevated water tanks forstorage. Elevated water tank is a large elevated water storage container constructed for thepurpose of holding a water supply at a height sufficient to pressurize a water distributionsystem. These structures have a configuration that is especially vulnerable to horizontalforces like earthquake due to the large total mass concentrated at the top of slender supportingstructure. So it is important to check the severity of these forces for particular region.The main purpose of this paper is to study the response of elevated water tank todynamic forces by both equivalents Static method as well as Dynamic method and to findbasic design parameters. It is also necessary to find out the effect of sloshing of water on roofslab of tank container during the earthquake. For seismic analysis, it is necessary to considerthe effect of hydrodynamic pressure on sides of container as well as base slab of container. Itis also necessary to consider the effect of pressure due to wall inertia & effect of verticalground acceleration in the seismic analysis of elevated water tank.REVIEW OF LITERATUREMuch of a literature has presented in the form of technical papers till date on thedynamic analysis of Elevated Water Tanks. Different issues and the points are covered in thatanalysis i.e. dynamic response to ground motion, sloshing effect on tank, dynamic responseof framed staging etc. Some of those are analyzed belowGeorge W. Housner [1963]The basic plot behind this paper was the Chilean Earthquake, took place in 1960. Inthis earthquake most of the elevated water tanks are totally collapse or badly distorted. Thispaper was clearly speaks about the relation between the motion of water in the tank withrespect to tank and motion of whole structure with respect to ground. He has considered threebasic conditions for this analysis. He said that if water tank is fully filled i.e. without freeboard then the sloshing effect of water is neglected, if the tank is empty then no sloshing aswater is absent. In above two cases water tower will behave as one-mass structure. But inthird case i.e. water tank is partially filled, the effect of sloshing must be considered. In thatcase the water tower will behave as two-mass structure. Finally he concluded that the tankfully filled is compared with the partially filled tank then it is seen that the maximum force towhich the half-full tank is subjected may be significantly less than half the force to which thefull tank is subjected. The actual forces may be as little as 1/3 of the forces anticipated on thebasic of a completely full tank.Sudhir Jain K. & U. S. Sameer [1991]IS code provision for seismic design of elevated water tanks have been revised. It isseen that, due to absence of a suitable value of performance factor for tanks, the codeprovision for rather low seismic design force for these structure. Simple expressions arederived, which allow calculations of staging stiffness, and hence the time period, whileincorporating beam flexibility. The code must include an appropriate value of performance
  3. 3. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 2, March - April (2013), © IAEME290factor, say 3.0 for calculation of seismic design force for water tanks. An earthquake designcriteria is incomplete, unless clear specifications are include on how to calculate the timeperiod. A method for calculating the staging stiffness including beam flexibility and withouthaving to resort to finite element type analysis has been presented. This method is based onwell-known portal method which has been suitably developed to incorporate the beamflexibility and the three dimensional behavior of the staging.Sudhir Jain K. & M. S. Medhekar [1993]The basic plot behind this paper is to modify & suggestion in IS: 1893-1984. The majorrevisions suggested are1. No provision for ground supported tanks with rigid & flexible walls in above IS code.This provision must be included in the seismic analysis.2. The single degree of freedom idealization of tank is to be replaced by two or threedegree of freedom idealization.3. A performance factor (K) of 3.0 is suggested for all types of tank.4. The bracing beam flexibility is to be included in the calculation of lateral stiffness ofsupporting system of tank.5. In the seismic analysis, the effect of Convective hydrodynamic pressure is to beincluded.6. A simplified hydrodynamic pressure distribution is suggested for stress analysis oftank wall.Sudhir K. Jain & Sajjad Sameer U [1993]The basic plot behind this paper is to modify and suggestions in IS: 1893-1984 &suggestion given by Sudhir K Jain & M.S.Medhekar. Above author considered all thesuggestion given by Sudhir Jain & Medhekar and added some extra suggestion –1. In the seismic analysis, the effect of accidental torsion must be included.2. An expression for calculating sloshing height of water may be introduced in the code.3. The effect of hydrodynamic pressure for tanks with rigid wall and the tanks withflexible wall should be considered separately, as force in the tanks with flexible wallis higher than those tanks with rigid wall.4. The stresses due to hydrodynamic pressure in the tank wall and base should be givenin the form of table.M. K. Shrimali & R. S. Jangid [2003]Earthquake response of elevated liquid storage steel tanks isolated by the linearelastomeric bearings is investigated under real earthquake ground motion. Two types ofisolated tank models are considered in which the bearings are placed at the base and top ofthe steel tower structure. The continuous liquid mass of the tank is modeled as lumped massknown as sloshing mass, impulsive mass and rigid mass. The corresponding stiffness constantassociated with these lumped masses have been worked out depending upon the properties ofthe tank wall and liquid mass.The mass of steel tower structure is lumped equally at top and bottom. Since thedamping matrix of the isolated tank system is non-classical in nature, the seismic response isobtained by the Newmark’s step-by step method. The response of two types of tanks, namelyslender and broad tanks, is obtained and a parametric study is carried out to study the effectsof important system parameters on the effectiveness of seismic isolation. The various
  4. 4. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 2, March - April (2013), © IAEME291important parameters considered are the tank aspect ratio, the time period of tower structure,damping and time period of isolation system. It has been shown that the earthquake responseof the isolated tank is significantly reduced. Further, it is also observed that the isolation ismore effective for the tank with a stiff tower structure in comparison to flexible towers. Inaddition, a simplified analysis is also presented to evaluate the response of the elevated steeltanks using two degree of freedom model and two single degree of freedom models. It isobserved that the proposed analysis predicts the seismic response of elevated steel tanksaccurately with significantly less computational efforts.O. R. Jaiswal & S. K. Jain [2005]Recognizing the limitations and shot comings in the provision of IS:1893-1984, Jainand Medhekar, Jain and Sameer a set of provisions on aseismic design of liquid storage tanks,the author has given some recommendations –1. Design horizontal seismic coefficient given in revised IS: 1893(Part-1)-2002 is usedand values of response reduction factor for different types of tanks are proposed.2. Different spring-mass model for tanks with rigid & flexible wall are done away with;instead, a single spring-mass model for both types of tank is proposed.3. Expressions for convective hydrodynamic pressure are corrected.4. Simple expression for sloshing wave height is used.5. New provisions are included to consider the effect of vertical excitation and todescribe critical direction of earthquake loading for elevated water tanks with frametype staging.R. Livaoglu & A. DogangunThis paper is specifically speaks about the response of supporting staging system ofwater towers. Author had considered frame supporting as well as cylindrical shell supportingsystem. The research shows that fluid-structure interaction can play an important role onseismic behavior of elevated water tanks. By considering both types of supporting system andseismic analysis was performed considering fluid-structure interaction. Conclusions from theanalysis results showed that supporting system may considerably change the seismic behaviorof the elevated water tanks.Displacement based Lagrangian approach is selected to model the fluid-elevated tankinteraction in this study. The fluid elements are defined by eight nodes with three translationaldegree of freedom at each node. It should be noted that, because of lack of a geometricalcapability in the Lagrangian FEM with brick shaped elements considered here.From the analysis carried out, author calculated the peak responses and correspondingtime period where the maximum roof displacement, sloshing displacement, base shear force& base moment are obtained. From the result, he found that the maximum responses areobtained between 9 and 10 seconds for frame support & 5 and 10 seconds for cylindricalshaft supports. Also he found that the roof displacement response for frame support is higherthan the cylindrical support. Change in displacement response values are considerably effectthe system seismic behavior. The sloshing responses are also affected by selected supportsystem and hence the effect on sloshing displacement cannot be neglected in the evaluation ofthe seismic behavior of the tanks. For the resign having seismic risk, the cylindrical shaftsupport system may be used because of having important advantages than the common usedframe type system.
  5. 5. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 2, March - April (2013), © IAEME292Gareane A. I. Algreane, S. A. Osman & O. A. Karim [2008]This paper is related with the soil & water behavior of elevated concrete water tankunder seismic load. An artificial seismic excitation has been generated according to Gaspariniand Vanmarcke approach, at the bedrock, and then consideration of the seismic excitationbased on one dimension nonlinear local site has been carried out. Author has chosen sevencases to make comparisons with direct nonlinear dynamic analysis, mechanical models withand without soil structure interaction (SSI) for single degree of freedom (SDOF), two degreeof freedom (2DOF), and finite element method (FEM) models. The analysis is based onsuperposition model dynamic analysis. Soil structure interaction (SSI) and fluid structureinteraction (FSI) have been accounted using direct approach and added mass approachrespectively. The result shows that a significant effect obtained in shear force, overturningmoment and axial force at the base of elevated tank.Lyes Khezzar, Abdennour Seibi & Afshin GoharzadehThis paper presents the steps involved in a test rig to study water sloshingphenomenon in a 560ൈ160ൈ185 mm PVC rectangular container subjected to sudden(impulsive) impact. The design encompasses the construction of the testing facility and thedevelopment of a proper data acquisition system capable of capturing the behavior of pre-and post-impact water motion inside the tank. Fluid motion was recorded a video camera forflow visualization purpose. Two water levels of 50 and 75% full as well as two drivingweights of 2.5 and 4.5 Kg were used. The experimental study was supplemented by acomputational fluid dynamics study to mimic the fluid motion inside the tank.The water sloshing phenomenon in a rectangular tank under sudden impact wasinvestigated experimentally & numerically. Design of the testing rig and selection of propersensors as well as data acquisition system was performed. Flow visualization of simulationand experimental results showed a good agreement. The water level for both simulation andexperimental results compared well during motion and showed a minor discrepancy afterimpact which may be due to tank bouncing. Contrary to previous studies, both experimentaland numerical results indicated the presence of a single traveling wave before the impact.Future study related to pressure measurements at the tank wall will be conducted forstructural analysis purposes.W. H. BoyceThe response of a simple steel water tank has been measured during earthquakes andvibration tests. Calculations of the period of vibration of the tank have been made takingground yielding and water sloshing into account. Excellent agreement has been obtainedbetween measured and calculated results. The response of the tower during the earthquakemotion has been calculated from ground accelerogram and the agreement between measuredand calculated response was found to be reasonable.From his experimental study he conclude that – (1) water sloshing must be consideredwhen calculating the period of vibration of water towers. The use of total water mass in 2-DOF simplification is not valid. (2) The simplification to 2-DOF system where groundyielding effects are accounted for equivalent spring stiffness of the tower is adequate andproduces the results agreeing well with experimental values. (3) The analytical producersused to calculate the response of structure from ground accelerograms provide a responsibleprediction of structure response.
  6. 6. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 2, March - April (2013), © IAEME293Dr. Suchita Hirde & Dr. Manoj Hedaoo [2011]This paper presents the study of seismic performance of the elevated water tank forvarious seismic zones of India for various heights and capacity of elevated water tanks fordifferent soil conditions. The effect of height of water tank, earthquake zones and soilconditions on earthquake forces have been presented in this paper with the help of analysis of240 models of various parameters.In this paper, the study is carried out on RCC circular elevated water tank with M-20grade of concrete and Fe-415 grade of steel & SMRF are considered for analysis. Elevatedwater tank having 50,000 liters and 100,000 liters capacity with staging height 12 m. 16 m,20 m, 24 m, 28 m considering 4 m height of each panels are considered for the study.Author has given following conclusions from his analysis – (1) Seismic forces aredirectly proportional to the Seismic Zones. (2) Seismic forces are inversely proportional tothe height of supporting system. (3) Seismic forces are directly proportional to the capacity ofwater tank. (4) Seismic forces are higher in soft soil than medium soil, higher in medium soilthan hard soil. Earthquake forces for soft soil is about 40-41% greater than that of hard soilfor all earthquake zones and tank full and tank empty condition.CONCLUSIONAnalysis & design of elevated water tanks against earthquake effect is of considerableimportance. These structures must remain functional even after an earthquake. Elevated watertanks, which typically consist of a large mass supported on the top of a slender staging, areparticularly susceptible to earthquake damage. Thus, analysis & design of such structuresagainst the earthquake effect is of considerable importance.After details study of all the papers, following points are to be consider at the time of seismicanalysis of elevated water tank1. In India, there is only one IS code i.e. IS 1893: 1984, in which provisions for aseismicdesign of elevated water tanks are given. IS 1893(Part-1): 2002 is the fifth revision ofIS 1893, still it is under revision. So detail criteria for aseismic analysis of elevatedwater tank are not mentioned in above IS code. Thus, the recommendations &suggestions given by all the above author has to be considered at the time of analysis.IITK-GSDMA has given some guidelines for seismic design of elevated water tankthat should consider at the time of analysis.2. Most elevated water tank are never completely filled with water. Hence, a two – massidealization of the tank is more appropriate as compared to one-mass idealization.3. Basically, there are three cases that are generally considered while analyze theelevated water tank – (1) Empty condition. (2) Partially filled condition. (3) Fullyfilled condition. For (1) & (3) case, the tank will behave as a one-mass structure andfor (3) case the tank will behave as a two-mass structure.4. If we compared the case (1) & (3) with case (2) for maximum earthquake force, themaximum force to which the partially filled tank is subjected may be less than half theforce to which the fully filled tank is subjected. Actual forces may be as little as 1/3 ofthe forces anticipated on the basis of a fully filled tank.5. During the earthquake, water in the tank get vibrates. Due to this vibration waterexerts impulsive & convective hydrodynamic pressure on the tank wall and the tankbase in addition to the hydrostatic pressure. The effect of impulsive & convectivehydrodynamic pressure should consider in the analysis of tanks. For small capacity
  7. 7. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 2, March - April (2013), © IAEME294tanks, the impulsive pressure is always greater than the convective pressure, but it isvice-versa for tanks with large capacity. Magnitudes of both the pressure are different.6. The effect of water sloshing must be considered in the analysis. Free board to beprovided in the tank may be based on maximum value of sloshing wave height. Ifsufficient free board is not provided, roof structure should be designed to resist theuplift pressure due to sloshing of water.7. Earthquake forces increases with increase in Zone factor & decreases with increase instaging height. Earthquake force are also depends on the soil condition.ACKNOWLEDGEMENTSI wish to thank the Management, Principal, Head of Civil Engineering Departmentand Staff of Jawaharlal Nehru Engineering College and authorities of Dr. BabasahebAmbedkar Marathwada University for their support.REFERENCES[1] George W. Housner, 1963 “The Dynamic Behaviour of Water Tank” Bulletin of theSeismological Society of America. Vol. 53, No. 2, pp. 381-387. February 1963[2] Jain Sudhir K., Sameer U.S., 1990, “Seismic Design of Frame Staging For Elevated WaterTank” Ninth Symposium on Earthquake Engineering (9SEE-90), Roorkey, December 14-16, Vol-1.[3] Sudhir K. Jain and M. S. Medhekar, October-1993, “Proposed provisions for aseismic designof liquid storage tanks” Journals of structural engineering Vol.-20, No.-03[4] Sudhir K Jain & Sajjed Sameer U, March-1994,Reprinted from the bridge and structuralengineer Vol-XXIII No 01[5] Sudhir K. Jain & O. R. Jaiswal, September-2005, Journal of Structural Engineering Vol-32,No 03[6] R. Livaoğlu and A.Doğangün May 2007 “An Investigation About Effects of SupportingSystems on Fluid-elevated Tanks Interaction” SS: Special Structures Paper ID: SS148, Tehran,Iraq.[7] S. A. Osman, O. Karim and A. Kasa, 2008 “Investigate The Seismic Response Of ElevatedConcrete Water Tank ” Engineering Postgraduate Conference (EPC)[8] Lyes Khezzar, Abdennour Seibi, Afshin Goharzadeh. “Water Sloshing In Rectangular Tanks –An Experimental Investigation & Numerical SIMULATION” International Journal ofEngineering (IJE), Volume (3) : Issue (2)[9] W.H. Boyce “Vibration Test on Simple Water Tower”[10] M.K.Shrimali, R.S.Jangid “Earthquake Response Of Isolated Elevated Liquid Storage Tank”[11] IITK-GSDMA guidelines for seismic design of liquid storage tanks.[12] I.S 1893-2002 criteria for earthquake resistant design of structures.[13] IS: 3370 (Part II) – 1965 code of practice for concrete structures for the storage of liquidspart ii reinforced concrete structures.[14] Dr. Suchita Hirde, Ms. Asmita Bajare, Dr. Manoj Hedaoo – 2011 “Seismic performance ofelevated water tanks”. International Journal of Advanced Engineering Research and StudiesIJAERS/Vol. I /Issue I / 2011/ 78-87[15] Damodar Maity, C. Naveen Raj and Indrani Gogoi, “Dynamic Response of Elevated LiquidStorage Elastic Tanks With Baffle”, International Journal of Civil Engineering & Technology(IJCIET), Volume 1, Issue 1, 2010, pp. 27 - 45, ISSN Print: 0976 – 6308, ISSN Online: 0976 –6316