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A STUDY ON RESPONSE REDUCTION FACTOR OF RC WATER TANK
By
MILAN H MANEK
(Enrolment No. 130540720006)
Guided By
Prof. D.K.JIVANI (M.E. CASAD)
Prof. Civil Engg. Dept., DIET, Hadala
A Thesis Submitted to
Gujarat Technological University
In partial Fulfilment of the Requirements for
The Degree of Master of Engineering
In Civil-Structural Engineering
JANUARY-2015
DARSHAN INSTITUTE OF ENGINEERING & TECHNOLOGY, RAJKOT-MORBIHIGHWAY, HADALA.
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CERTIFICATE
A STUDY ON
RESPONSE REDUCTION FACTOR OF RC WATER TANK Mr.
MILAN H MANEK 130540720006
Seal of Institute
This is to certify that the work embodied in this dissertation entitledwas carried out by
(Enrolment No. ) at D.I.E.T., Hadala for partial fu lfilmentto M.E. Civil Engg.(Structural) degree to be awarded by Gujarat Technological University.This research work has been carried out under my supervision and is to my satisfaction.
Date:Place: Hadala
Prof. D.K.Jivani Dr. R. G. Dhamsania
(Guide) Principal
D.I.E.T, Hadala D.I.E.T, Hadala
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DECLARATION OF ORIGINALITY
Signature of Student:
Name of Student: MILAN H MANEK
Enrollment No: 130540720006 Signature of Guide:
Name of Guide: PROF. Dipak K. Jivani
Institute code: 054
I hereby certify that I am the sole author of this thesis and that neither any part of this thesis northe whole of the thesis has been submitted for a degree to any other University or Institution.
I certify that, to the best of my knowledge, my thesis does not infringe upon anyonescopyright nor violate any proprietary rights and that any ideas, techniques, quotations, or any
other material from the work of other people included in my thesis, published or otherwise, are
fully acknowledged in accordance with the standard referencing practices. Furthermore, to the
extent that I have included copyrighted material that surpasses the bounds of fair dealing
within the meaning of the Indian Copyright Act, I certify that I have obtained a writtenpermission from the copyright owner(s) to include such material(s) in my thesis and haveincluded copies of such copyright clearances to my appendix.
I declare that this is a true copy of my thesis, including any final revisions, as approved by mythesis review committee.
Date:
Place: RAJKOT
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THESIS APPROVAL
This is to certify that research work embodied in this entitled A
STUDY ON RESPONSE REDUCTION FACTOR OF RC WATER TANK
Mr. MILAN H MANEK (Enroll No.130540720006) at Darshan institute
of Engineering and Technology, Rajkot
Date:
Place:
Examiner(s):
( ) ( ) ( )
----------------------- ---------------------- --------------------------
was
carried out by
is approved for award of the degree of M.E.
Civil (St ructure) by Gujarat Technological University.
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ACKNOWLEDGMENTS
MILAN H MANEK
Enroll No.130540720006
I would like to extend my heartiest thanks with a deep sense of gratitude and respect to all
those who provided me immense help and guidance during the research.
I would like to thank my dissertation guide Prof. D. K. JIVANI Professor,
Structural Engineering department, DIET, Rajkot for providing a vision about the
dissertation. I have been greatly benefited from the regular critical reviews and
inspiration throughout my work.
I would also like to thank my Professors for their unfailing cooperation and
sparing their valuable time to assist me in my work. I have developed not only technical skills
but also learned a ll those qualities required to become a good professional engineer.
Last but not least, I would like to mention here that I am greatly indebted to each and
everybody who has been associated with this research at any stage but whose name does not
find a place in this acknowledgment.
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ABSTRACT
The main purpose of earthquake resisting design is is that the structure should not
permitted to collapse but damage is allowed during earthquake. water tank is importantstructure. Staging type of tanks are generally collapse during earthquake , so it is required
to calculate earthquake load perfectly. Past evidence had shown that the elevated tanks are
vulnerable due to earthquake. The tanks are designed based on linear elastic methods
which are considered only elastic range. factor shows the reserved strength of water tank.in
IS 1893-2002(part-2)value of R factor for RC elevated shaft supportd tank is 1.8 and for
column supported 2.5. One constant R-value for elevated water tank cannot reflect the
expected inelastic behavior of all elevated water tanks located in different seismic
zone and having different staging pattern.So it is required to find out perfect value of R
factor for various type of RC elevated tank individually. The present study efforts are
made to evaluate the response reduction factor of RC framed staging elevated water tank
having varying staging height, capacities, staging type and zones. The main objective
of this study is to verify the R factor of most common designed Elevated Intze tank through
comparing the assumed R factor during design to actual R factor obtained from non-linear
analysis.
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TABLE OF CONTENTS
Title Page No.
ACKNOWLEDGEMENTS.............................................................................................. 5
ABSTRACT...................................................................................................................... 6
TABLE OF CONTENTS...................................................................................................7
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INDEX
CHAPTER 1 INTRODUCTION.9
CHAPTER 2 LITERATURE REVIEW12
1.1 Overview91.2 Need For the Present Study..10
1.3 Objective ..11
1.4 Scope of work...................................11
2.1paper1.12
2.2paper 2....15
2.3paper 3....17
2.4 paper 4.................................................. ................................................... ...........................18
2.5paper 520
2.6 paper 6....21
2.7 paper 7....22
2.8 paper 8................................ ........................................................ ........................................23
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CHAPTER-1 INTRODUCTION
1.1 Over View:
Water Is Considered As The Source Of Every Creation And Is Thus A Very Crucial Element For
Humans To Live A Healthy Life. High Demand Of Clean And Safe Drinking Water Is Rising
Day By Day As One Can Not Live Without Water. It Becomes Necessary To Store Water. Water
Is Stored Generally In Concrete Water Tanks And Later On It Is Pumped To Different Areas To
Serve The Community.
One Of The Oldest Known Water Tanks In Kenya Was Built By The Railway At Makindu River
In 1907. It Appears The Tank Was Connected To A Hydram Pump That Used The Power Of The
Flowing Water In The River To Push Water Into The Tank From Where It Was Used By Steam
Locomotives.
Water Tanks Can Be Classified As Overhead, Resting On Ground Or Underground Depending
On Their Location. The Tanks Can Be Made Of Steel Or Concrete. Tanks Resting On Ground
Are Normally Circular Or Rectangular In Shape And Are Used Where Large Quantities Of
Water Need To Be Stored.
Overhead Water Tanks Are Used To Distribute Water Directly Through Gravity Flow And Are
Normally Of Smaller Capacity. As The Overhead Water Tanks Are Open To Public View, TheirShape Is Influenced By The Aesthetic View In The Surroundings.
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1.2 Need Of Study:
R As Per International Standards For Elevated Tanks:
Generally Staging Type Over Head Tanks Collapse In Earthquake . It Is Very Important To
Consider Earthquake Load In Design Of Elevated Tank.
Response Reduction Factor (R) Is Very Important To Find Out Earthquake Load.The Response
Reduction Factor Reflects The Capacity Of Structure To Dissipate Energy By Inelastic Behavior.
The Values Of Response Reduction Factor(R) Of Rc Elevated Water Tank Are Given In Is
1893 Draft Code, Which Is Arrived At Empirically Based On Engineering Judgment. The
Values Of Response Reduction Factor Of Elevated Water Tank Adopted By Difference
Codes/Standards Are Summaries Below.
odes/Standards R Factor
bc 2000/ Fema 368 .5 To 3.0
ci 350.3 .0 To 4.75
s:1893-2002(Part -2) Rcc Frame Support
Draft Code)
.8 (Omrf)
Smrf)
The Value Of R-Factor Is Fixed 2.5 For Frame Supported Rc Elevated Tank.One Constant
R-Value For Elevated Water Tank Cannot Reflect The Expected Inelastic Behavior Of All
Elevated Water Tanks Located In Different Seism ic Zone And Having Different
Capacities.So It Is Required To Find Out Perfect Value Of R Factor For Various Type Of Rc
Elevated Tank Individually.
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1.3 Objectives:
1.5Scope Of Work:
The Main Objective Of This Study Is To Verify The R Factor Of Most Common
Designed Elevated Intze Tank Through Comparing The Assumed R Factor During
Design To Actual R Factor Obtained From Non-Linear Analysis. The Specific
Objectives Of The Study Are To:
Conduct Static Non-Linear (Pushover) Analysis And Calculate R Factor Of E levated
Intze Tank
Prepare A Spreadsheet To Design Elevated Tank
Compare The Calculated R Factor With The Assumed R Factor.
Evaluate Ductility, Redundancy And Over Strength Factor Of Elevated Intze Tank
Study The Effect Of Staging Height And Staging Type On Response Reduction Factor
(R).
To Study Effect Of Zone Factor On Response Reduction Factor (R).
To Prepare A Spreadsheet And Design Water Tank As Per Is- 3370:2009 (Limit State
Method).
Understand The Procedure Of Water Tank Modelling And Pushover Analyses In SapSoftware Considering Hydrodynamic Pressure As Per Iitk-Gsdma Guidelines.
To Perform Pushover Analysis Of Elevated Water Tank For Different Capacity, Height ,
Zone And Compare The Results.
Perform A Comparative Study Between Different Staging Patterns In Form Of Variation In
Ductility, Redundancy And Over Strength Factor Etc
Calculated And Compare The Calculated R Factor With The Assumed R Factor
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Chapter-2 Litrature Review
2.1 Evaluation Response Reduction Factor Of Rc Framed Staging ElevatedWater Tank Using Static Pushover Analysis( Tejash Patel1, Jignesh Amin2,
Bhavin Patel3 1- Post Graduate Student, Svit, Vasad, October, 2013
Published On February 2014
215)
Severe Damages Were Observed In Buildings, Public Utility Structures Like Water Tanks And
Hospitals During 26th January 2001 Bhuj Earthquake. Earthquake Can Induce Large Horizontal
And Overturning Forces In Elevated Water Tanks And Are Quite Vulnerable To Damage InEarthquakes Due To Their Basic Configuration Involving Large Mass Concentrated At Top
With Relatively Slender Supporting System. The Basic Principal Of Designing Structures For
Strong Ground Motion Is That The Structure Should Not Collapse But Damage To The
Structural Elements Is Permitted. Since A Structure Is Allowed To Be Damaged In Case Of
Severe Shaking, The Structure Should Be Designed For Seismic Forces Much Less Than What
Is Expected Under Strong Shaking, If The Structures Were To Remain Linearly Elastic.
Response Reduction Factor Is The Factor By Which The Actual Base Shear Force Should Be
Reduced, To Obtain The Design Lateral Force. Base Shear Force Is The Force That Would Be
Generated If The Structure Were To Remain Elastic During Its Response To The Design Basic
Earthquake (Dbe) Shaking. Ozhendekci Et Al. (2006) Evaluated The Seismic Response
Modification Factor For Eccentrically Braced Frames. Conclusion Was Made That One
Constant R-Value Cannot Reflect The Expected Inelastic Behavior Of All Building Which Have
The Same Lateral Load Resisting System. Pore Et Al. (2006) Described Effect Of Response
Reduction Factor In Performance Based Seismic Design Of Rc Building For India.
The Values Of Response Reduction Factor Of Rc Elevated Water Tank Are Given In Is 1893
(Part-Ii) 2002, Which Is Arrived At Empirically Based On Engineering Judgment. The Values
Of Response Reduction Factor Of Elevated Water Tank Adopted By Difference
Codes/Standards Are Summaries In Table.
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odes/Standards R Factor
bc 2000/ Fema 368 .5 To 3.0
ci 350.3 .0 To 4.75
s:1893-2002(Part -2) Rcc Frame Support
Draft Code)
.8 (Omrf)
.5 (Smrf)
One Constant R-Value For Elevated Water Tank Cannot Reflect The Expected Inelastic
Behavior Of All Elevated Water Tanks Located In Different Seismic Zone And Having
Different Capacities. In The Present Study Efforts Are Made To Evaluate The Response
Reduction Factor Of Five Existing Rc Framed Staging Elevated Water Tanks Having Staging
Height Of 12 M But Having Varying Capacities. The Effects Of Seismic Zone And Fundamental
Time Period Of Water Tank On The Response Reduction Factor Are Also Discussed
The Concept Of R Factor Is Based On The Observations That Well Detailed Seismic Framing
Systems Can Sustain Large Inelastic Deformations Without Collapse And Have Excess Of
Lateral Strength Over Design Strength. Response Reduction (R) Factors Are Essential SeismicDesign Tools, Which Are Typically Used To Describe The Level Of Inelasticity Expected In
Lateral Structural Systems During An Earthquake. The Response Reduction Factor (R) Is
Depends On Over Strength (Rs), Duct ility (R), Redundancy (Rr).
Over Strength Factor (Rs) Accounts For The Yielding Of A Structure At Load Higher Than The
Design Load Due To Various Partial Safety Factors, Strain Hardening, Oversized Members,
Confinement Of Concrete. Non-Structural Elements Also Contribute To The Over Strength.
Ductility Factor (R) Is A Ratio Of Ultimate Displacement Or Code Specified Permissible
Displacement To The Yield Displacement. Higher Ductility Implies That The Structure Can
Withstand Stronger Shaking Without Collapse. Redundancy Factor (Rr) Depends On The
Number Of Vertical Framing Part icipate In Seismic Res istance. Yielding At One Location In
The Structure Does Not Imply Yielding Of The Structure As A Whole. Hence The Load
Distribution, Due To Redundancy Of The Structure, Provides Additional Safety Margin.
Concept Of Response Reduction Factor:
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In Present Study Five Rc Elevated Water Tanks Having A Capacity Of 20m3, 30m3, 50m3,
60m3, And 70m3 Are Considered. For All The Tanks, The Height Of Staging Is 12m And
Staging Comprise Of 4 Columns.
Etabs V.9.5 Software Is Used To Perform The Non Linear Static Pushover Analysis. The Rc
Beams And Columns Are Modeled As 3-D Frame Elements With Centerline D imension. Slabs
Are Modeled As Membrane Elements And Are Assumed To Behave As Rigid Diaphragms.
Column Foundations Are Assumed To Be Fixed. Damping Ratio Of 5 Percent Is Assumed For
All Natural Modes. Flexure Moment (M3), Axial Biaxial Moment (P-M2-M3) And Axial
Compressive Shear Force (V) Hinges Are Assigned At The Face Of Beam, Column, And
Bracing Respectively Using The Static Pushover Analysis.
In Order To Achieve The Objective, The Following Procedure Was Adopted 1. Developing A
Three Dimensional Model Of Existing Rc Frame. 2. Application Of Gravity Loads, Live Loads,Water Load, Etc. 3. Application Of Static Lateral Load Induced Due To Earthquake, At Cg Of
Container 4. Developing M-T & V- ? Relationship For Rc Trestle. 5. Pushing The Structure
Using The Load Patterns Of Static Lateral Loads, To Displacements Larger Than Those
Associated With Target Displacement Using Static Pushover Analysis 6. Developing Pushover
Curve And Estimating The Force And Deformations In Each Element At The Level Of
Displacement Corresponding To Target Displacement 7. In This Study The Response Reduction
Factor (R) Of Exiting Rc Framed Elevated Water Tank Having A 12m Height Of Staging But
Different Capacities Are Evaluated. The Significant Outcomes Of Works Are Summarized As
Follows: 1. The Response Reduction Factor Is Considerably Affected By The Seismic Zone And
Fundamental Time Period Of Water Tanks. It Reduces As The Seismic Zone Increases And
Increases As The Fundamental Time Period Increases. 2. To Ensure The Consistent Level Of
Damaged, Values Of Response Reduction Factor Should Be Based On Both Fundamental Period
Of The Staging And Type Of Soil. 3. The Values Of Response Reduction Factor For A Given Rc
Framing System Should Vary Between Seismic Zones. Also The Reinforcement Detailing
Requirements Should Vary With Seismic Zone. 4. Estimation Of Response Reduction Factor
With Exact Analysis Will Help In An Economical Design. 5. It Is Observed That Response
Reduction Varies From 2.63 To 4 For Tank In Full Condition In Seismic Zone V.
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2.2 Formulation Of Response Reduction Factor For Rcc Framed Staging Of
Elevated Water Tank Using Static Pushover Analysis
(Mr. Bhavin Patel And Mrs. Dhara Shah)Earthquake Can Induce Large Horizontal And Overturning Forces In Elevated Water Tanks.
Such Tanks Are Quite Vulnerable To Damage In Earthquakes Due To Their Basic Configuration
Involving Large Mass Concentrated At Top With Relatively Slender Supporting System. When
The Tank Is In Full Condition, Earthquake Forces Almost Govern The Design Of These
Structures In Zones Of High Seismic Activity. It Is Important To Ensure That The Essential
Requirement Such As Water Supply Is Not Damaged During Earthquakes. In Extreme Cases,
Total Collapse Of Tanks Shall Be Avoided. However, Some Repairable Damage May Be
Acceptable During Shaking Not Affecting The Functionality Of The Tanks
Evere Damages Were Observed In Buildings, Public Utility Structures Like Water Tanks And
Hospitals During 26th January 2001 Bhuj Earthquake. Is:18931984 Does Not Count The
Convective Hydrodynamic Pressures In The Analysis Of Tank Wall And Assumes The Tank As
A Single Degree Of Freedom Idealization. The Accurate Approach For Analysis Of Water Tank
Is To Model The Tank With Two Masses Representing The Impulsive As Well As Convective
Components Of Liquid. Lots Of Research Has Been Made In Two Mass Model Of Esr And
Hydrodynamic Analysis Of The Container. It Has Also Been Observed That A Well Designed
And Well Constructed Water Tank Can Withstand More Lateral Loads Than It Is Designed For
Due To Three Reasons: Over Strength (Rs) Redundancy (Rr) Ductility (R) The Response
Reduction Factor Or Force Modification Factor R Reflects The Capacity Of Structure To
Dissipate Energy Through Inelastic Behavior. It Is A Combined Effect Of Over Strength,
Ductility And Redundancy Represented As
R = Rs * Rr * R.
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Conclusion
There Is No Mathematical Basis For The Response Reduction Factor Tabulated In Indian Design
Codes.
A Single Value Of R For All Buildings Of A Given Framing Type, Irrespective Of Plan And
Vertical Geometry, Cannot Be Justified. But For Esr Staging (BeamColumn Frame Or Shaft),
Where The Basic System Of Framing And Behavior Is More Or Less Common, The Method Can
Be Derived To Evaluate RFactor. Similar Effort Has Been Made Here.
To Ensure The Consistent Level Of Damage, Values Of R Should Depend On Both Fundamental
Period Of The Staging And The Soil Type.
The Values Assigned To R For A Given Framing System Should Vary Between Seismic Zones.
Also Detailing Requirements Vary By Zone.
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2.3 Review Of Code Provisions On Design Seismic Forces For Liquid Storage
Tanks
It Is Well Recognized That Liquid Storage Tanks Possess Low Ductility And Energy Absorbing
Capacity As Compared To The Conventional Buildings. Accordingly, Various Design CodesProvide Higher Level Of Design Seismic Forces For Tanks. In This Article, Provisions Of Ibc
2000, Aci, Awwa, Api, Eurocode 8 And Nzsee Guidelines Are Reviewed, To Assess The
Severity Of Design Seismic Forces For Tanks Vis--Vis Those For Buildings. It Is Seen That,
Depending On The Type Of Tank, Design Seismic Force For Tanks Can Be 3 To 7 Times Higher
Than That For Buildings. Based On The Comparison Of Provisions In These Documents,
Various Similarities, Discrepancies And Limitations In Their Provisions Are Brought Out.
This Article Presents An Assessment Of Design Seismic Force For Tanks Vis- -Vis Design
Seismic Force For Buildings As Mentioned In The Following Documents:
(A) Ibc 2000
(B) Aci Standards Aci 371 (1998) And Aci 350.3 (2001)
(C) Awwa D-100 (1996), Awwa D-103 (1997), Awwa D-110 (1995) And Awwa D-115 (1995)
(D) Api 650 (1998)
(E) Eurocode 8 (1998)
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2.4 Criteria For Design Of Rcc Staging For Overhead Water Tanks
Liquid Tanks Are Important Public Utility And Industrial Structures. Specifications, The Design
And Construction Method In Reinforced Concrete Are Influenced By The Prevailing
Construction Practices, The Physical Properties Of The Material And The Environmental
Conditions.
While The Common Methods Of Design Have Been Covered In This Standard Code, Design Of
Structures Of Special Forms Or In Unusual Circumstances Should Be Left To The Judgment Of
The Design Engineer And In Such Cases Special Systems Of Design & Construction May Be
Permitted On Production Of Satisfactory Evidence Regarding Their Adequacy And Safety By
Analysis Or Test Or By Both
This Draft Standard Lays Down Criteria For Analysis, Design And Construction Of Reinforced
Cement Concrete Staging Of Framed Type With Columns Or Shaft Type, For Achieving A
Desirable Level Safety And Durability Of The Supported Liquid Storage Structure (Container).
Container May Consist Of Any Material Like Rcc, Fiber Concrete, Ferrocement, Steel, Pvc,
Etc.While The Provisions Of This Standard Refer To Stagings For The Storage Of Liquids, The
Recommendations Are Applicable Mainly To Water Storage Or Containment.
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2.5 An Investigation of Seismic Response Reduction Factor for Earthquake
Resistant Design(International Journal of Latest Trends in Engineering and
Technology (IJLTET))
Conclusion:
The present study estimates the seismic Response reduction factor (R) of reinforced concretespecial moment resisting frame (SMRF) with and without shear wall using static nonlinear
(pushover) analysis. Calculation of Response reduction factor(R) is done as per the new
formulation of Response reduction factor (R) given by Applied Technology Council (ATC)-19
which is the product of Strength factor (Rs), Ductility factor (R) and Redundancy factor (RR).
The analysis revealed that these three factors affects the actual value of response reduction factor
(R) and therefore they must be taken into consideration while determining the appropriate
response reduction factor to be used during the seismic design process. The actual values
required for determination of Response reduction factor (R) is worked out on the basis of
pushover curve which is a plot of base shear verses roof displacement. Finally the calcu lated
values of Response reduction factor(R) of reinforced concrete special moment resisting frame
(SMRF) with and without shear wall are compared with the codal values.
Based on above results and observations the following conclusions are drawn.
International Journal of Latest Trends in Engineering and Technology (IJLTET)
1) The Response reduction factor without shear wall is almost reduced by 50% considering
displacement ductility ratio as compared to IS Code values.
2) The Response reduction factor with shear wall are almost doubled considering rotational
ductility ratio as compared to IS code values.
3) The Response reduction factor without shear wall considering rotational ductility ratio was
found to approximately same as compared to IS code values.
4) In case of buildings with shear wall considering rotational ductility ratio there is significant
difference between Response reduction factors and IS code values.5) The Response reduction factor with shear wall considering displacement ductility ratio was
found to approximately same as compared to IS code values.
6) In case of buildings without shear wall considering displacement ductility ratio there is
significant difference between Response reduction factors and IS code values.
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2.6 Seismic Behavior Of Shell-Base Connections In Large Storage
Tanks(Alain Nussbaumer, Martin Kolle 1steel Structures Laboratory
(Icom), Swiss Federal Institute Of Technology, Lausanne, Switzerland)
Conclusions:
Unanchored Steel Tanks Subjected To Strong Ground Motion May Experience Rocking MotionIf The Moment Generated By The Inertial Mass Of The Content Stored Is Greater Than The
Resisting Moment Provided By The Weight Of The Tank And Its Content. Rocking Of The
Tank Causes The Shell-Base Welded Connection To Undergo Cycles Of Rotation. The
Eurocode Provides A Methodology For Estimating The Maximum Rotation That This
Connection May Experience. This Methodology Was Applied To Study Six Tanks Located In
Switzerland And It Was Found That Four Of These Tanks Did Not Satisfy The Rotation Limit
Set By The Code. These Findings Motivated A More Comprehensive Study In Which Two
Tanks Were Analyzed According The Eurocode And New Zealands Recommendations, And
By Means Of A Pushover And A Time History Analysis.
This Paper Investigated The Rotation Demand Provided By The Eurocode, The New Zealands
Recommendations, A Pushover Analysis And A Time History Analysis. Eurocode Results Were
Too Conservative For The Slender Tank (I.E., Rmlang), But Relatively Acceptable For The
Squat Tank Studied (I.E., Mellingen). On The Other Side, The New Zealands
Recommendations And The Pushover Analysis Provided Values Between The Average And
The Maximum Rotation Measured From The Time History Analysis. While More Work Is
Needed To Have Final Conclusions Regarding The Demand Of The Tank, This Investigation
Clearly Points Out That The Eurocode Does Not Provide The Right Means To Estimate The
Rotation Of The Shell-Base Connection In An Above Ground Unanchored Tank.The Time
History Analysis, Explained In Section 3, Provides The Most Information Of The Shell-Base
Connection Behavior. It Provides The Response History Of Deformation And Rotation At The
Connection, From Which The Number Of Cycles And The Amplitude Of Each Cycle AreObtained. The Time History Analysis Is However A Very Time Consuming Procedure,
Requiring That Ground Motions Representative Of The Site Hazard Be Obtained. The
Procedure Is Also Very Expensive Computationally. On The Other Hand, The Pushover
Analysis Can Provide A Good Overall Understanding Of The Behavior Of The Tank While
Being Significantly Less Expensive Than The Time History Analysis.
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2.7 A Case Study Considering A 3-D Pushover Analysis Procedure
( W. Huang And P. L. Gould The 14 Th World Conference On Earthquake
Engineering , October 12-17, 2008, Beijing, China )
Objectives:
Conclusions:
With An Unusually Large Rectangular Duct Opening Located About 1/3 Of The Height Above
The Base, A 115 Meter High Reinforced Concrete Chimney Collapsed During The Earthquake
While Several Other Similar Structures Survived With Only Moderate Damage. Debris Of The
Failed Stack Cut Many Lines, Which Fueled Fires That Shut Down The Refinery For Months.
This Case Study Provides Intriguing Results, Considering That The Stack Was Designed And
Constructed According To International Standards And Is Representative Of Similar Structures
At Refineries Throughout The World. The Main Focus Of The Investigation Is The Dynamic
Response Of The Stack Due To An Earthquake Motion Recorded At A Nearby Site, Named The
Ypt Record. A New 3-D Pushover Analysis Procedure Is Proposed In This Paper And The
Results Will Be Compared With Those Of A Nonlinear Dynamic Analysis. Higher Mode Effects
Are Significant For This Type Of Structure And Considered In The Proposed 3-D Pushover
Analysis Procedure.
To Evaluate The Original Design Of The Collapsed Chimney, Known As The Tpras Stack,
Using Current Analysis Techniques.
To Evaluate The Design Of A Similar Size Chimney Representative Of U. S. Practice
To Explain Why The Single Stack In Question Did Indeed Collapse While Several Similar
Structures In The Same Vicinity Survived With Minimal Damage Through The Use Of
Advanced Seismic Evaluation Tools.
To Extend The Pushover Analysis Procedure For Chimney Structures By Taking Into Account
The Higher Modes And The Three Dimensional Interaction Effects.
A New 3-D Pushover Analysis Procedure Was Proposed And Applied To Models Of Chimneys
With And Without An Opening. Various Lateral Load Patterns Were Considered. For The
Target Displacement Of The Model Without The Opening, The Error From The Uniform
Distribution Was The Largest, While The Mode 1 Distribution, Elf Distribution, And Triangle
Distribution Provided Somewhat Better Estimates. The Srss Distribution Gave A Good
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Prediction, With An Error Around 10% And The Error From The Mpa Procedure Was Even Less
Than 10%. As To The Peak Deflections, The Mpa Procedure And Srss Distribution Provided
The Best Estimates, While The Uniform Distribution Underestimated The Total Response By
Up To 30%. The Mode 1 Distribution, Elf Distribution, And Triangle Distribution Gave Similar
Estimates. Compared To A 2-D Pushover Analysis, The New 3-D Pushover Analysis Procedure
Provides A Better Estimation For Target Displacements.
For The 3-D Pushover Analysis On The Model With The Opening, The Failure Displacements
Predicted Using Different Lateral Patterns Were In An Acceptable Range. The Srss Distribution
Resulted In The Lowest Error, Between 10% And 20%. All Of The Lateral Load Patterns
Successfully Captured The Shear Cracks Developed Around The Opening, Along With Flexural
Cracks.
From The Failure Cracking Pattern For The 3-D Nonlinear Dynamic Analysis, There Were MoreLong Critical Shear Cracks Around The Opening Area Than There Were The Flexural Cracks
Along The Height. This Confirmed The Initial Prediction By 2-D Pushover Analysis That The
Critical Shear Cracking Around The Opening Area, Along With The Concentrated Flexural
Cracking, Was Prominent In The Failure.
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2.8 Pushover Analysis Of A 19 Story Concrete Shear Wall Building
(Rahul Rana, Limin Jin And Atila Zekioglu)
Conclusion:
Pushover Analysis Was Performed On A Nineteen Story, Slender Concrete Tower Building
Located In San Francisco With A Gross Area Of 430,000 Square Feet. Lateral System Of TheBuilding Consists Of Concrete Shear Walls. The Building Is Newly Designed Conforming To
1997 Uniform Building Code, And Pushover Analysis Was Performed To Verify Code's
Underlying Intent Of Life Safety Performance Under Design Earthquake
Building Analyzed Is A N ineteen Story (18 Story + Basement), 240 Feet Tall Slender Concrete
Tower Located In San Francisco With A Gross Area Of 430,000 Square Feet. Unique Features
Of The Slender Concrete Tower Presented Challenges For Seismic Design. Typically, A 240
Feet Tall Concrete Building In Seismic Zone 4 Would Have A Lateral System That Combines
Shear Walls And Moment Frames. However, Two Architectural Features Made The Use Of
Moment Frames Difficult. First, The 60 Feet Long Open Bays Limited The Number Of
Possible Moment Frames. Second, On The Southeast Side Two Of The Perimeter Columns Are
Discontinued At The 6th Story And Six New Columns Are Introduced That Slope For The
Lowest Six Stories At An Angle Of About 20 Degrees From Vertical. These Sloped Columns
Connect To Transverse Walls Through Horizontal Transfer Elements At The 6th Story And Put
Considerable Gravity-Induced Horizontal Loads On The Lateral System At That Level.
Sap2000 Was Used To Perform Pushover Analysis And Etabs Was Used To Calculate HingeProperties Of Shear Wall And Elastic Analysis. For All Lateral Elements, Cracked Section
Was Assumed With An Effective Stiffness Equal To 50% Of Gross Section.
Pushover Analysis Is A Useful Tool Of Performance Based Seismic Engineering To Study
Post-Yield Behavior Of A Structure. It Is More Complex Than Traditional Linear Analysis,
But It Requires Less Effort And Deals With Much Less Amount Of Data Than A Nonlinear
Response History Analysis. Pushover Analysis Was Performed
On A Nineteen Story Concrete Building With Shear Wall Lateral System And Certain Unique
Design Features. Utilizing The Results From This Analysis, Some Modifications Were Made
To The Original Code-Based Design So That The Design Objective Of Life Safety Performance
Is Expected To Be Achieved Under Design Earthquake.
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Chapter-3 RESPONSE REDUCTION FACTOR
Response reduction factor is the factor by which the actual base shear force
should be reduced ,to obtain the design lateral force.
the response reduction factor reflects the capacity of st ructure to dissipate
energy by inelastic behavior . This process is combined effect of over
strength , redundancy and ductility.
Response reduction factor is also known as ratio of maximum elastic force
to designed force.
Response reduction factor is depended on three factors .over strength factor
ductility factor
redundancy factor.
Over strength factor calculated for yielding of structure at load higher than
the designed load due to various partial safety factors, strain hardening ,
over sized members , confinement of concrete.
Ductility factor is ratio of ultimate displacement or code specified
displacement to the yield displacement.
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been obtained according to
GSDMA guidelines and is added to tank walls according to Westergaard
approach.
TWO MASS IDEALIZATION
Concept proposed in IITK-GSDMA guidelines.
Separated pressure in to impulsive and convective parts.impulsive mass Liquid in lower region of tank behaves like mass
rigidly connected to tank which accelerate along with tank
convective mass liquid in upper region that undergoes sloshing
motion
Analysis of elevated tank under seismic load of fluid structure interaction
has been investigated by added mass approach.
In present work impulsive mass has
A finite element model is used to model the elevated tank system using
SAP2000 software.
Columns and beams in the frame type support system are modeled as
frame elements.
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Description of water tank:
SAP software is used to perform the non linear static
pushover analysis.
The RC beams and columns are modeled as 3-D frame elements with
centerline dimension.
Wall and domes are modeled as shell elements.
Column foundations are assumed to be fixed.
Default hinges are considered for analysis
Flexure moment (M3), axial biaxial moment (P-M2-M3) and axial
compressive shear force (V) hinges are assigned at the face of beam,
column, and bracing respectively using the static pushover analysis.
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SAP software is used to perform the non linear static
pushover analysis.
The RC beams and columns are modeled as 3-D frame elements with
centerline dimension.
Wall and domes are modeled as shell elements .
Column foundations are assumed to be fixed.
Default hinges are considered for analysis
Flexure moment (M3), axial biaxial moment (P-M2-M3) and axial
compressive shear force (V) hinges are assigned at the face of beam,column, and bracing respectively using the static pushover analysis.
Fig shows Pushover analysis procedure :
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Pushover curve of 20m3 water tank:
For 12m
For 16m
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For 20m
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TANK TYPE:INTZ TANK COLUMN SIZE:650MM DIASTAGING HEIGHT 12M COLUMN STEEL: 10 -20mm
STAGING TYPE6 COL
CIRCULAR ZONE IV
FULL EMPTY
TIME PERIOD 0.68 0.51
BASE SHEAR 311 193
DUCTILITY FACTOR 0.86 0.86
REDUNDANCY FACTOR 1.283 1.3
OVERSTRENGTH FACTOR 2.733 4.15
R 2.94 4.65
TANK TYPE:INTZ TANK COLUMN SIZE:650MM DIA
STAGING HEIGHT 16M COLUMN STEEL:12 -20mm
STAGING TYPE6 COL
CIRCULAR ZONE IV
FULL EMPTY
TIME PERIOD 0.9 0.68
BASE SHEAR 280 174
DUCTILITY FACTOR 0.86 0.86
REDUNDANCY FACTOR 0.7645 1.03
OVERSTRENGTH FACTOR 2.392 3.79
R 1.57 3.36
TANK TYPE:INTZ TANK COLUMN SIZE:650MM DIA
STAGING HEIGHT 20M COLUMN STEEL:14-20mm
STAGING TYPE6 COL
CIRCULAR ZONE IV
FULL EMPTY
TIME PERIOD 1.25 0.955
BASE SHEAR 328 233
DUCTILITY FACTOR 0.86 0.86
REDUNDANCY FACTOR 0.799 0.84
OVERSTRENGTH FACTOR 1.89 3.66
R 1.3 2.65
Result tables:
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0
50
100
150
200
250
300
350
12m 16m 20m
FULL
EMPTY
0
0.2
0.4
0.6
0.8
1
1.2
1.4
12m 16m 20m
FULL
EMPTY
0
0.5
1
1.5
22.5
3
3.5
4
4.5
5
12m 16m 20m
FULL
EMPTY
Effect of staging ht on r facto :
BaseShear(kN
Staging Height (m)
RedundancyFacto
Staging Height (m)
RFact
Staging Height (m)
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0
0.2
0.4
0.6
0.8
1
1.2
1.4
12m 16m 20m
FULL
EMPTY
0
0.5
1
1.5
2
2.5
3
3.5
12 14 16 18 20
REDUNDANCY FACTOR
OVERSTRENGTH FACTOR
R Factor
0
0.5
1
1.52
2.5
3
3.5
4
4.5
5
12 14 16 18 20
REDUNDANCY FACTOR
OVERSTRENGTH FACTOR
R Factor
TimePeriod(sec
Staging Height (m)
Facto
Staging Height (m)
250m3 (Tank Full)
F
act
Staging Height (m)
250m3 (Empty)
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0
0.5
1
1.5
22.5
3
3.5
0 0.5 1 1.5
REDUNDANCY FACTOR
OVERSTRENGTH FACTOR
R Factor
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0 0.2 0.4 0.6 0.8 1 1.2
REDUNDANCY FACTOR
OVERSTRENGTH FACTOR
R Factor
Facto
Time Period (sec)
250m3 (Tank Full)
Facto
Staging Height (m)
250m3 (Empty)
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Conclusion:
The elevated tanks Fundamental time period increases with increase in
tank staging height. Also time period increases with the tank filling
condition.
The critical response occurs in case of full tank conditions. This result may
be due to the fact that the hydrodynamic pressures higher in tank full case
as compared to tank empty.
Base shear decreases as the staging height increases that is due to increase
in Time period and the dispersion of base shear is increased when thepercentage of the filling in the storage tanks are increased.
The response reduction factor is considerably affected by the
fundamental time period of water tanks. It reduces as the fundamental time
period increases.
Estimation of response reduction factor with exact analysis will help in an
economical design.
It is observed that response reduction varies from 2.63 to 4 for tank in full
condition in seismic zone IV.