The document discusses seismic base isolation as an earthquake-resistant technique for buildings in regions of low to moderate seismicity. It analyzes a 10-story residential building in Dhaka, Bangladesh using base isolators. Static and dynamic analyses were performed on the building both with and without isolators. The results showed that the use of isolators significantly reduced base shear and moment demands. While isolators increase initial costs, the reduction in reinforcement requirements overall makes base isolation more cost-effective. Thus, the document concludes that base isolation is a suitable technique even for buildings in areas of low seismicity.

1. SEISMIC BASE ISOLATION FOR
BUILDINGS IN REGIONS OF LOW TO
MODERATE SEISIMICITY
A.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
TABLE1
DATA ANALYSED VALUES
STRUCTURAL TIME PERIOD 0.913sec
DESIGN BASE SHEAR(EQ LOAD) 4565KN
DESIGN BASE SHEAR(WIND LOAD) 2698KN
MAXIMUM TOP STORY DISPLACEMENT(EQ LOAD) 13.63mm
MAXIMUM TOP STORY DISPLACEMENT(WIND LOAD) 6.63mm
TOTAL WEIGHT OF THE BUILDING 127766KN
GOVERNING AXIAL LOAD UNDER COLUMN C3 7215KN
GOVERNING AXIAL LOAD UNDER COLUMN C2 4546KN
GOVERNING 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 TABLE2
ELASTROMER UNITS VALUE
PROPERTIES
SHEAR MODULUS KPa 400
ULTIMATE ELONGATION % 65
MATERIAL CONSTANT k ---- 0.87
ELASTIC MODUKUS KPa 1350
15

16. SEISMIC LOADS AND STRUCTURAL DATA TABLE3
SEISMIC PROPERIES VALUE
SEISMIC ZONE FACTOR 0.15
SOIL PROFILE TYPE S3
SEISMIC COEFFICIENT CA 0.22
SEISMIC COEFFICIENT CV 0.32
ISOLATED LATERAL FORCE COEFFICIENT RI 2
FIXED BASE LATERAL FORCE COEFFICIENT R 8
IMPORTANCE FACTOR 1
SEISMIC COEFFICIENT CAM 0.35
SEISMIC 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 TABLE4
BEARING TYPES AND LOAD DATA LRB HDRB TOTAL
TYPE ISOLATO ISOLATOR
R1 1
NO OF BEARINGS 16 9 25
AVERAGE DEAD LOAD+SLL(KN) 4035 7024
MAXIMUM DEAD LOAD+LL(KN) 4546 7215
MAXIMUM DEAD 4063 7220
LOAD+SLL+EQL(KN)
SEISMIC WEIGHT W(KN) 127766
TOTAL 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 DHAKA
EARTHQUAKE
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 ANALYSIS
DESIGN BASE SHEAR(KN) IN X 22221 19610
DIRECTION
DESIGN BASE SHEAR(KN) IN Y 16666 14528
DIRECTION
DESIGN BASE MOMENT(KN-M) 143114 123726
IN X DIRECTION
DESIGN BASE MOMENT(KN-M) 87047 76880
IN Y DIRECTION
TOP STORY 67.1 35
DISPLACEMENT(mm) IN U1
DIRECTION
TOP STORY 40.1 31.7
DISPLACEMENT(mm) IN U1
DIRECTION
25

26. RESULTS OF DYNAMIC ANALYSIS USING
ISOLATOR TABLE 6
STRUCTURAL PERIOD FOR MODE ISOLATOR TOTAL
1 DISPLACEMENT STRUCTURAL
DRIFT
U1 DIRECTION(STATIC ANALYSIS) 151.6 56.3
U2 DIRECTION(STATIC ANALYSIS) 145.8 53.1
U1 DIRECTION(RESPONSE 134.4 35.4
SPECTRUM ANALYSIS)
U2 DIRECTION(RESPONSE 83.3 31.2
SPECTRUM ANALYSIS)
U1 DIRECTION(TIME HISTORY 119.1 30.1
ANALYSIS)
U2 DIRECTION(TIME HISTORY 73.8 28.6
ANALYSIS)
26

27. BASE SHEAR AND BASE MOMENT AFTER
DYNAMIC ANALYSIS TABLE7
RESPONSE SPECTRUM TIME HISTORY
ANALYSIS ANALYSIS
DESIGN BASE 8842.5 7803.2
SHEAR(KN) IN X
DIRECTION
DESIGN BASE 5526.9 4837.3
SHEAR(KN) IN Y
DIRECTION
DESIGN BASE 49923.7 43932.1
MOMENT(KN-M) IN X
DIRECTION
DESIGN BASE 30955.67 26.930.8
MOMENT(KN-M) IN Y
DIRECTION
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 BUILDING
TABLE8
NO OF SAVINGS NO OF ISOLATOR NET NET
STORIES 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 BEAMS
AND 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
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