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  • 1. SEISMIC BASE ISOLATION FOR BUILDINGS IN REGIONS OF LOW TO MODERATE SEISIMICITYA.B.M. SAIFUL ISLAM, SYED ISHTIAQ,MOHAMEMMED JAMMEL MEMBERS OF ASCE PRACTICAL PERIODICAL ON STRUCTURAL DESIGN & CONSTRUCTION ,ASCE FEB 2012 BETHU PRAVEEN KUMAR(12CE65R11) STRUCTURAL ENGINEERING DEPARTMENT OF CIVIL ENGINEERING IIT KHARAGHPUR 1
  • 2. OVERVIEW EARTH QUAKE RESISTANT STRUCTURES EARTHQUAKE RESISTANT STRUCTURE BY BASE ISOLATION A TEN STOREY BUILDING IN DHAKA IS TAKEN AND ANALYSED RESULTS INSIGHTS CONCLUSIONS TYPICAL REFERENCES 2
  • 3. EARTHQUAKE RESISTANT STRUCTURES WHY DO WE NEED EARTHQUAKE RESISTANT STRUCTURES? WHAT DO WE DO TO MAKE A STRUCTURE EARTHQUAKE RESISTANT? TECHNIQUES USED FOR EAARTHQUAKE RESISTANT STRUCTURES 3
  • 4. EARTHQUAKE RESISTANT STRUCTURES BY BASE ISOLATION WHAT IS BASE ISOLATION? HOW DOES IT WORKS? MATERIAL USED AS BASE ISOLATORS LRB(1970’S) AND HDRB(1980’S) 4
  • 5. CONT SUITABILITY OF BASE ISOLATORS APPLICATION OF BASE ISOLATOR PARAMETERS REQUIRED FOR SIESMIC BASE ISOLATION 5
  • 6. CONT PRELIMINARY EXPLORATION OF THE SUITABILITY OF BASE ISOLATOR SOPHISTICATED FEM SOFTWARE SAP2000 HAS BEEN USED FOR ANALYSIS OF THE STRUCTURE IMPLEMENTATION OF BI IS A SUITABLE ALTERNATIVE AS IT INCREASES FLEXIBILITY AND REDUCES LATERAL FORCES 6
  • 7. ISOLATION DESIGN FLOW CHART FLOW CHART FOR SEQUENTIAL ISOLATOR DESIGN IS GIVEN 7
  • 8. EXPERIMENT A TEN STOREY RESIDENTIAL BUILDING LOCATED IN DHAKA OF 4 SPACING AT 7.62M C/C SPACING IN BOTH DIRECTIONS IS ANALYSED ESSENTIAL DATA REQUIRED FOR ANALYSIS IS SHOWN BELOW THE PLAN AND ELEVATION IS SHOWN 8
  • 9. PLAN AND ELEVATION OF BUILDING 9
  • 10. ESSENTIAL DATA Fck = 28 MPa FY = 414MPa DEAD LOAD EXCLUDING SELF WEIGHT = 4.8 N/mm2 LIVE LOAD = 2.4 KN/mm2 SLAB THICKNESS = 150mm EXTERIOR CORNER COLUMNS C1=750mmX750mm EXTERIOR MIDDLE COLUMNS C2=950mmX950mm 10
  • 11. CONT INTERIOR COLUMNS C3=1000mmX1000mm GRADE BEAMS GB=300mmX375mm GB1=525mmx825mm GB2=600mmx900mm GB3=550mmX900mm 11
  • 12. EXPERIMENT EQUIVALENT STATIC ANALYSIS OF THE CONVENTIONAL FIXED BUILDING IS DONE BY BNBC BUT FOR ISOLATED BUILDINGS RESPONSE REDUCTION FACTOR=2 AND IMPORTANCE FACTOR=1 IS TAKEN THE STATIC ANALYSIS RESULTS ARE SHOWN IN TABLE 1 12
  • 13. STATIC ANALYSIS WITHOUT USING ISOLATOR TABLE1DATA ANALYSED VALUESSTRUCTURAL TIME PERIOD 0.913secDESIGN BASE SHEAR(EQ LOAD) 4565KNDESIGN BASE SHEAR(WIND LOAD) 2698KNMAXIMUM TOP STORY DISPLACEMENT(EQ LOAD) 13.63mmMAXIMUM TOP STORY DISPLACEMENT(WIND LOAD) 6.63mmTOTAL WEIGHT OF THE BUILDING 127766KNGOVERNING AXIAL LOAD UNDER COLUMN C3 7215KNGOVERNING AXIAL LOAD UNDER COLUMN C2 4546KNGOVERNING AXIAL LOAD UNDER COLUMN C1 2544KN 13
  • 14. ISOLATION DESIGN RUBBER ISOLATORS ARE DESIGNED CONSIDERING VERTICAL LOADS,ISOLATOR TYPES THE MATERIAL DEFINITIONS IN TABLE2 IS THE BASIC INFORMATION FOR DESIGN PROCESS TABLE3 PROVIDES THE INFORMATION OF THE SEISMIC LOADS AND STRUCTURAL DATA 14
  • 15. MATERIAL DEFINITIONS TABLE2ELASTROMER UNITS VALUEPROPERTIESSHEAR MODULUS KPa 400ULTIMATE ELONGATION % 65MATERIAL CONSTANT k ---- 0.87ELASTIC MODUKUS KPa 1350 15
  • 16. SEISMIC LOADS AND STRUCTURAL DATA TABLE3SEISMIC PROPERIES VALUESEISMIC ZONE FACTOR 0.15SOIL PROFILE TYPE S3SEISMIC COEFFICIENT CA 0.22SEISMIC COEFFICIENT CV 0.32ISOLATED LATERAL FORCE COEFFICIENT RI 2FIXED BASE LATERAL FORCE COEFFICIENT R 8IMPORTANCE FACTOR 1SEISMIC COEFFICIENT CAM 0.35SEISMIC COEFFICIENT CVM 0.55 16
  • 17. CONT HDRB AND LRB HAVE BEEN ASSIGNED AT THE MIDDLE C3 AND OUTSIDE C1 AND C2 COLUMNS RESPECTIVLEY TYPES OF ISOLATORS AND LOADS ACTING ON THE COLUMN BASE SUBJECTED TO BEARINGS IS SHOWN IN TABLE4 17
  • 18. TYPES OF ISOLATORS AND LOADS TABLE4BEARING TYPES AND LOAD DATA LRB HDRB TOTALTYPE ISOLATO ISOLATOR R1 1NO OF BEARINGS 16 9 25AVERAGE DEAD LOAD+SLL(KN) 4035 7024MAXIMUM DEAD LOAD+LL(KN) 4546 7215MAXIMUM DEAD 4063 7220LOAD+SLL+EQL(KN)SEISMIC WEIGHT W(KN) 127766TOTAL WIND LOAD(KN) 2698 18
  • 19. ISOLATOR PERFORMANCE THE TWO MAIN THHINGS NEEDED TO TAKE CARE ARE 1)THE STATUS OF THE ISOLATOR BEARING TO SUPPORT THE LOAD SAFELY 2)THE PERFORMANCE OF ISOLATED BEARING WHICH IS EVALUATED FOR BOTH DEB AND MCE THE COEFFICINTS TAKEN FOR ANALYSIS ARE SHOWN 19
  • 20. CONT SEISMIC COEFFICENT CORRESPONDING TO CONSTANT ACCELERATION REGION FOR DBE(CA) = 0.22 FOR MCE(CAM)= 0.35 SEISMIC COEFFICIENT CORRESPONDING TO CONSTANT VELOCITY REGION FOR DBE(CV) = 0.32 FOR MCE(CVM)= 0.55 ZONE FACTOR FOR DHAKA = 0.15 20
  • 21. DYNAMIC ANALYSIS ASSIGNING THE PROPERTIES TO THE ISOLATORS AND LINKED TO THE STRUCTURE AND IS ANALYSED FROM THE TIME HISTORY OF THE NEAREST EQ,SOIL CHARACTERISTICS,SEISIMIC COEFFICIENTS,ALONG WITH GENERATED TIME HISTORY DUHAMELS INTEGRAL 5% DAMPED RESPONSE SPECTRUM IS ESTABLISHED 21
  • 22. CONT THEN AFTER LINKING THE BI TO THE STRUCTURE THE DYNAMIC ANALYSIS,RESPONSE SPECTRUM AND TIME HISTORY IS PERFORMED WITH 2 MODIFICATIONSACCOUNTING FOR BI 1)SPRINGS WITH EFFECTIVE STIFFNESS OF THE ISOLATOR ARE MODELED TO CONNECT THE BASE LEVEL OF THE STRUCTURE TO GROUND 2)THE RESPONSE SPECTRUM IS MODIFIED TO ACCOUNT FOR DAMPING PROVIDED IN ISOLATED MODES TO USE A COMPOSITESPECTRUM.THE 5% DAMPING SPECTRUM HAS BEEN REDUCED BY B FACTOR IN ISOLATED MODES 22
  • 23. COMPOSITE RESPONSE SPECTRUM FOR DHAKAEARTHQUAKE 23
  • 24. RESULTS DYNAMIC ANALYSIS OF FIXED BUILDING IS PERFORMED BY SAP AND THE RESULTS ARE SHOWN IN TABLE5 LINEAR STATIC AND NON LINEAR DYNAMIC ANALYSIS OF THE BUILDING WITH ISOLATORS ARE AS SHOWN IN TABLE 6 AND TABLE7 24
  • 25. DYNAMIC ANALYSIS OF FIXED BUILDING TABLE5 RESPONSE TIME HISTORY SPECTRUM ANALYSIS ANALYSISDESIGN BASE SHEAR(KN) IN X 22221 19610DIRECTIONDESIGN BASE SHEAR(KN) IN Y 16666 14528DIRECTIONDESIGN BASE MOMENT(KN-M) 143114 123726IN X DIRECTIONDESIGN BASE MOMENT(KN-M) 87047 76880IN Y DIRECTIONTOP STORY 67.1 35DISPLACEMENT(mm) IN U1DIRECTIONTOP STORY 40.1 31.7DISPLACEMENT(mm) IN U1DIRECTION 25
  • 26. RESULTS OF DYNAMIC ANALYSIS USINGISOLATOR TABLE 6STRUCTURAL PERIOD FOR MODE ISOLATOR TOTAL1 DISPLACEMENT STRUCTURAL DRIFTU1 DIRECTION(STATIC ANALYSIS) 151.6 56.3U2 DIRECTION(STATIC ANALYSIS) 145.8 53.1U1 DIRECTION(RESPONSE 134.4 35.4SPECTRUM ANALYSIS)U2 DIRECTION(RESPONSE 83.3 31.2SPECTRUM ANALYSIS)U1 DIRECTION(TIME HISTORY 119.1 30.1ANALYSIS)U2 DIRECTION(TIME HISTORY 73.8 28.6ANALYSIS) 26
  • 27. BASE SHEAR AND BASE MOMENT AFTERDYNAMIC ANALYSIS TABLE7 RESPONSE SPECTRUM TIME HISTORY ANALYSIS ANALYSISDESIGN BASE 8842.5 7803.2SHEAR(KN) IN XDIRECTIONDESIGN BASE 5526.9 4837.3SHEAR(KN) IN YDIRECTIONDESIGN BASE 49923.7 43932.1MOMENT(KN-M) IN XDIRECTIONDESIGN BASE 30955.67 26.930.8MOMENT(KN-M) IN YDIRECTION 27
  • 28. CONT SINCE ALL THE VALUES OF BASE SHEAR AND DESIGN BASE MOMENT HAS DRASTICALLY REDUCED BY INATALLATION OF ISOLATOR SO IT IS SATISFACTORY TO USE BI 28
  • 29. ECONOMIC IMPLICATIONS THOUGH THE INSTALLATION OF ISOLATION SYSTEM ADDS MORE TO INITIAL COST IT REDUCES THE REINFORCEMENT REQUIRMENTS OF BUILDINGAND ULTIMATELY REDUCES THE COST COST ANALYSIS FOR A 10 STORY BUILDING IS PERFORMED FOR A 10 STORY BUILDING SAVING IN REINFORCEMANT REQUIRMENT ALONG WITH INITIAL COSTS ARE DETERMINED IN TABLE8 29
  • 30. NET SAVINGS IN THE ISOLATED BUILDINGTABLE8NO OF SAVINGS NO OF ISOLATOR NET NETSTORIES FROM ISOLATOR COSTS IN SAVINGS SAVINGS BEAMS S US $ IN US $ % OF AND REINFORC COLUMNS EMENT IN $10 40980 25 24926 16054 7.75 30
  • 31. CONT FOR THE SAME PLAN AREA BUILDINGS HAS BEEN NALYSED FOR 4,5,6,7,8,9 STOREY TO REPRESENT A COMPARITIVE GENERALISED RELATIONSHIP FOR SAVINGS IN REINFORCEMENT FOR AN ISOLATED BUILDINGS 31
  • 32. % SAVINGS IN REINFORCEMENT FOR BEAMSAND COLUMNS VERSUS DIFFERENT STORIES 32
  • 33. INSIGHTS DUE TO VAST CIVILISATION AND URBANISATION MANY REGIONS OF EARTH ARE GOING TO BE EARTHQUAKE PRONE IN FUTURE SINCE THE BASE ISOLATION CAN ACCOMIDATE FOR IT EVEN WITH SOME COST REDUCTION IT MAY BE WIDELY USED IN FUTURE 33
  • 34. CONCLUSIONS EVEN THOUGH SEISMIC BASE ISOLATION INCREASES THE INITIAL COST THE REDUCTION IN REINFORCEMENT IN UPPER FLOORS WILL MAKE UP THAT COST AND EVEN REDUCES THE TOTAL COST EVEN BI BUILDINGS PROVE EFFECTIVE FOR LOW TO MEDIUM RISE BUILDINGS WITH A GOOD FOUNDATION SOIL. 34
  • 35. REFERENCES BANGLADESH NATIONAL BUILDING CODE(19993) HOUSING AND BUILDING RESEARCH INSTITUTE DEB S.K(2004) “SEISMIC BASE ISOLATION – AN OVERVIEW” 35
  • 36. THANK YOU 36