Seismic performance of circular elevated water tank with framed staging

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Seismic performance of circular elevated water tank with framed staging

  1. 1. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME159SEISMIC PERFORMANCE OF CIRCULAR ELEVATED WATERTANK WITH FRAMED STAGING SYSTEMGaikwad Madhukar V.1Prof. Mangulkar Madhuri N.21P. 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.ABSTRACTWater tank is used extensively for storage water, inflammable liquids, and otherchemicals. The current analysis and design of supporting structures of elevated water tanksare extremely vulnerable under lateral forces due to an earthquake and the Bhuj earthquakeprovided illustration when a great many water tank staging’s suffered damage and a fewcollapses. The aim of this paper is to understand the behavior of Elevated Water Tank withthe framed staging in lateral earthquake loading using IITK-GSDMA Guidelines byconsidering two theoretical theories given by Sudhir Jain &Sameer U. S. [1990] and RapidAssessment of Seismic Safety of Elevated Water Tank with framed staging & SoftwareSTAAD Pro.-2007,for calculate the lateral stiffness. Same values of lateral stiffness Ks isused for further analysis. After details study it was found that the lateral stiffness Ksobtainedby using Rapid Assessment of Seismic Safety of Elevated Water Tank gives the optimumvalue of Base Shear and Base Moment and hence it is economical. The design based onabove 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 watertanks for storage. Elevated water tank is a large elevated water storage container constructedINTERNATIONAL JOURNAL OF ADVANCED RESEARCH INENGINEERING AND TECHNOLOGY (IJARET)ISSN 0976 - 6480 (Print)ISSN 0976 - 6499 (Online)Volume 4, Issue 4, May – June 2013, pp. 159-167© IAEME: www.iaeme.com/ijaret.aspJournal Impact Factor (2013): 5.8376 (Calculated by GISI)www.jifactor.comIJARET© I A E M E
  2. 2. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME160for the purpose of holding a water supply at a height sufficient to pressurize a waterdistribution system. These structures have a configuration that is especially vulnerable tohorizontal forces like earthquake due to the large total mass concentrated at the top of slendersupporting structure. So it is important to check the severity of these forces for particularregion.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 onthe time period. Often, column stiffness is considered as 12EI/ L3, which is based on theassumption that bracing beams are infinitely rigid. In practice, these beams are flexible andtherefore 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 arefixed against rotation. For the most commonly used staging, having all the columns along theperiphery of a circle, panel stiffness is obtained as below-Kpanel=ଵଶ ா௖ ூ௖ ே௖௛ଷቈቀಶ್಺್ಽቁቀಶ್಺್ಽቁାଶ‫כ‬ቀಶ೎಺೎೓ቁ቉For Intermediate panels, and ……. (1)Kpanel=ଵଶ ா௖ ூ௖ ே௖௛ଷቈቀಶ್಺್ಽቁቀಶ್಺್ಽቁାଵ‫כ‬ቀಶ೎಺೎೓ቁ቉For Top & Bottom panels.…….. (2)Lateral Stiffness of Staging Ks-Ks =ଵ∑ ቀభ಼೛ೌ೙೐೗ቁಿ೛೔సభ. ……….. (3)When Tank structure is located on soft soil, the support is not rigid and hencebottommost panel is no more fixed against rotation. Under these condition, the panel stiffnessis 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 offramed type supporting system by considering the effect of girder flexibility. For tank stagingwith equal panel heights, identical columns arranged along the periphery of a circle, andidentical bracing girders, the lateral stiffness of the staging Ks is calculated as below –ଵ௄௦=ଵ௄௙௟௘௫௨௥௘൅ଵ௄௔௫௜௔௟Where ………. (4)ଵ௄௙௟௘௫௨௥௘= ∑ ቀଵ௄௣௔௡௘௟ቁே௣௜ୀଵKpanel=ଵଶ ா௖ ூ௖ ே௖௛ଷቈቀ಺್ಽቁቀ಺್ಽቁାଶ‫כ‬ቀ಺೎೓ቁ቉ For Intermediate panel …… (5)Kpanel=ଵଶ ா௖ ூ௖ ே௖௛ଷቈቀ಺್ಽቁቀ಺್ಽቁାଵ‫כ‬ቀ಺೎೓ቁ቉ For Topmost and bottommost panel …. (6)
  3. 3. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME161Kaxial =ଶே௖ ஺௖ ா ோ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 SoftwareLateral stiffness of staging is defined as the force required to be applied at the CG oftank so as to get a corresponding unit deflection. From the deflection of CG of tank due to anarbitrary lateral force one can get the stiffness of staging.STADD Pro software is used tomodel the staging.II. CASE STUDY1. Numerical Problem StatementA RC circular water container of 200 m3capacity has internal diameter of 8.50 m andheight of 3.82 m (including freeboard of 0.3 m). It is supported on RC staging consisting of 6columns of 550 mm dia. with horizontal bracings of 300 x 550 mm at four levels. The lowestsupply 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 groundlevel. Tank is located on soft soil in seismic zone III. Grade of staging concrete and steel areM20 and Fe415, respectively. Density of concrete is 25 KN/m3. Analyze the tank for seismicloads.Elevated water tank can be analyzed by both the condition i.e. for tank full conditionand tank partially filled condition.
  4. 4. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME1621.1 Preliminary DataTable 1: Sizes of various componentsSr. No. Components Size (mm)1 Roof Slab 175 Thick2 Wall 225 Thick3 Floor Slab 225 Thick4 Gallery 110 Thick5 Floor Beams 300 *6006 Braces 300 *5507 No of Column 068 Dia. of Column 5501.2 Formulation of ProblemTable 2: Constants which are considered for calculationSr. No. Constant Values Remarks1 Z 0.16 Structure assumed in Zone III2 I 1.5 Importance Factor3 R 3.0 Response Reduction Factor4 M-20 Grade of Concrete5 Fe- 415 Grade of Steel1.3 Details of Tank Geometry
  5. 5. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME1631.4 Change in Iteration with respect to volume:Table 3: Table showing change in iterations with respective to volumeSr, No. IterationsVolume inLit.Diameter ofcontainer inmeterHeight oftank inmeterFree Boardof Tank inmeter01 1 200,000 8.50 3.82 0.3002 2 8.00 4.28 0.3003 3 7.50 4.90 0.3004 4 7.00 5.50 0.3005 5 6.50 6.40 0.30III. ITERATION OF RESULTS BY GRAPHICAL METHODIteration of Results includes the graphical representation of output parameters whichare calculated as a solution.Graph No 01: Comparison of Lateral Stiffness obtained by Software & Theoretical MethodGraph No 02: Comparison of Base Shear obtained by Software & Theoretical Method forStatic Full condition0500010000150002000025000300001 2 3 4 5LateralStiffnessIteration NoComparison of Lateral StiffnessRapid- S. Jain STAAD Pro751752753751 2 3 4 5BaseShearIteration NoComparison of Base Shear for Static full condition-Rapid- S. Jain STAAD Pro.
  6. 6. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME164Graph No 03: Comparison of Base Shear obtained by Software & Theoretical Method forStatic Empty conditionGraph No 04: Comparison of Base Shear obtained by Software & Theoretical Method forHydrodynamic Full conditionGraph No 05: Comparison of Base Shear obtained by Software &Theoretical Method forHydrodynamic Empty condition501502501 2 3 4 5BaseShearIteration NoComparison of Base Shear for Hydrodynamic EmptyconditionRapid S. Jain STAAD Pro.501001502002501 2 3 4 5BaseShearIteration NoComparison of Base Shear for Static Empty conditionRapid- S. Jain STAAD Pro.1502002503001 2 3 4 5BaseShearIteration NoComparison of Base Shear for Hydrodynamic FullconditionRapid- S. Jain STAAD Pro.
  7. 7. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME165Graph No 06: Comparison of Base Moment obtained by Software & Theoretical Method forHydrostatic full conditionGraph No 07: Comparison of Base Moment obtained by Software & Theoretical Method forHydrostatic Empty conditionGraph No 08: Comparison of Base Moment obtained by Software & Theoretical Method forHydrodynamic Full condition20003000400050001 2 3 4 5BaseMomentIteration NoComparison of Base Moment for Hydrodynamic Fullcondition-Rapid- S. Jain STAAD Pro25003500450055001 2 3 4 5BaseMoment-Iteration NoComparison of Base Moment for Hydrodstatic Fullcondition-Rapid S. Jain STAAD Pro.20002500300035001 2 3 4 5BaseMomentIteration No.Comparison of Base Moment for Hydrostatic Emptycondition-Rapid- S. Jain STAAD Pro.
  8. 8. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME166Graph No 09: Comparison of Base Moment obtained by Software & Theoretical Method forHydrodynamic Empty conditionGraph No. 10: Comparison of Total Hydrodynamic Pressure by Software & TheoreticalMethod for Hydrodynamic Analysis of Elevated Water TankIV. CONCLUDING REMARKSFrom above mentioned detailed study and analysis some of the conclusion can bemade as follow ……Graph No 1 clearly shows the comparison of Lateral Stiffness obtained from threedifferent methods. If we observe the graph, the value of Ks obtained from Sudhir Jain andSTAAD Pro. is higher than the Rapid Assessment of seismic safety. If we analyze theelevated 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 beuneconomical. 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 Emptycondition by using three different methods for Hydrostatic& Hydrodynamic Analysis of01234561 2 3 4 5HydrodynamicPressure-Iteration NoComparison of Hydrodynamic Pressure-Rapid- S. Jain STAAD Pro.260028003000320034001 2 3 4 5BaseMoment-Iteration NoComparison of Base Moment for HydrodynamicEmpty condition-Rapid- S. Jain STAAD Pro.
  9. 9. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME167Elevated Water Tank. The values of Base Shear obtained from Tank full condition is greaterthan the Tank Empty condition and hence considered for further analysis. If we observe thegraphs we find that the Base Shear obtained from Rapid Assessment of seismic safety islesser than the other two, and hence it is economical.Graph No. 6 To 9 shows the comparison of Base Moment for Tank full and Emptycondition by using three different methods for Hydrostatic & Hydrodynamic Analysis ofElevated Water Tank. Base Moment obtained from Rapid Assessment of seismic safety islower than other two. If we design by considering the higher value we get over stabilized orsay over reinforced section. It is safe but uneconomical. That’s why Hydrostatics system ofdesigning of elevated water tank is not useful in seismic Zones. And hence, IS code provisionfor static analysis is restricted for small capacities of tanks only. For Hydrodynamic analysisthe Base Moment obtainsfrom Rapid Assessment of seismic safety is lesser than the othertwo, and hence it is economical.Graph No 10 shows the comparison of Hydrodynamic pressure on wall as well as onbase of Elevated Water tank. Total hydrodynamic pressure obtained from Rapid Assessmentof 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 onLateral Stiffness Ks obtained from Rapid Assessment of Earthquake safety of Elevated WaterTanks with Frame Staging is most economical and safe.V. 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]. IITK-GSDMA Guidelines for Seismic Design of Liquid Storage Tanks Provision withcommentary 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 TimePeriod 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 oflateral stiffness.[7]. Mangulkar Madhuri N. and Gaikwad Madhukar V., “Review on Seismic Analysis ofElevated 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 andDynamic 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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