Embed Size (px)
DESCRIPTION
Citation preview
1
SEISMIC BASE ISOLATION FOR BUILDINGS IN REGIONS OF LOW TO
MODERATE SEISIMICITY
A.B.M. SAIFUL ISLAM, SYED ISHTIAQ,MOHAMEMMED JAMMELMEMBERS OF ASCE
PRACTICAL PERIODICAL ON STRUCTURAL DESIGN & CONSTRUCTION ,ASCE FEB 2012
BETHU PRAVEEN KUMAR(12CE65R11)STRUCTURAL ENGINEERING
DEPARTMENT OF CIVIL ENGINEERING IIT KHARAGHPUR
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
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
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)
5
CONT
SUITABILITY OF BASE ISOLATORS
APPLICATION OF BASE ISOLATOR
PARAMETERS REQUIRED FOR SIESMIC BASE ISOLATION
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
7
ISOLATION DESIGN FLOW CHART
FLOW CHART FOR SEQUENTIAL ISOLATOR DESIGN IS GIVEN
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
9
PLAN AND ELEVATION OF BUILDING
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
11
CONT
INTERIOR COLUMNS C3=1000mmX1000mm
GRADE BEAMS GB=300mmX375mm
GB1=525mmx825mm
GB2=600mmx900mm
GB3=550mmX900mm
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
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
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
15
MATERIAL DEFINITIONS TABLE2
ELASTROMER PROPERTIES
UNITS VALUE
SHEAR MODULUS KPa 400
ULTIMATE ELONGATION % 65
MATERIAL CONSTANT k ---- 0.87
ELASTIC MODUKUS KPa 1350
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
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
18
TYPES OF ISOLATORS AND LOADS TABLE4BEARING TYPES AND LOAD DATA
LRB HDRB TOTAL
TYPE ISOLATOR1
ISOLATOR1
NO OF BEARINGS 16 9 25
AVERAGE DEAD LOAD+SLL(KN) 4035 7024
MAXIMUM DEAD LOAD+LL(KN) 4546 7215
MAXIMUM DEAD LOAD+SLL+EQL(KN)
4063 7220
SEISMIC WEIGHT W(KN) 127766
TOTAL WIND LOAD(KN) 2698
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
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
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
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
23
COMPOSITE RESPONSE SPECTRUM FOR DHAKA EARTHQUAKE
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
DYNAMIC ANALYSIS OF FIXED BUILDING TABLE5
RESPONSE SPECTRUM ANALYSIS
TIME HISTORY ANALYSIS
DESIGN BASE SHEAR(KN) IN X DIRECTION
22221 19610
DESIGN BASE SHEAR(KN) IN Y DIRECTION
16666 14528
DESIGN BASE MOMENT(KN-M) IN X DIRECTION
143114 123726
DESIGN BASE MOMENT(KN-M) IN Y DIRECTION
87047 76880
TOP STORY DISPLACEMENT(mm) IN U1 DIRECTION
67.1 35
TOP STORY DISPLACEMENT(mm) IN U1 DIRECTION
40.1 31.7
25
26
RESULTS OF DYNAMIC ANALYSIS USING ISOLATOR TABLE 6
STRUCTURAL PERIOD FOR MODE 1
ISOLATOR DISPLACEMENT
TOTAL STRUCTURAL DRIFT
U1 DIRECTION(STATIC ANALYSIS) 151.6 56.3
U2 DIRECTION(STATIC ANALYSIS) 145.8 53.1
U1 DIRECTION(RESPONSE SPECTRUM ANALYSIS)
134.4 35.4
U2 DIRECTION(RESPONSE SPECTRUM ANALYSIS)
83.3 31.2
U1 DIRECTION(TIME HISTORY ANALYSIS)
119.1 30.1
U2 DIRECTION(TIME HISTORY ANALYSIS)
73.8 28.6
27
BASE SHEAR AND BASE MOMENT AFTER DYNAMIC ANALYSIS TABLE7
RESPONSE SPECTRUM ANALYSIS
TIME HISTORY ANALYSIS
DESIGN BASE SHEAR(KN) IN X DIRECTION
8842.5 7803.2
DESIGN BASE SHEAR(KN) IN Y DIRECTION
5526.9 4837.3
DESIGN BASE MOMENT(KN-M) IN X DIRECTION
49923.7 43932.1
DESIGN BASE MOMENT(KN-M) IN Y DIRECTION
30955.67 26.930.8
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
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
30
NET SAVINGS IN THE ISOLATED BUILDING TABLE8
NO OF STORIES
SAVINGS FROM BEAMS AND COLUMNS IN $
NO OF ISOLATORS
ISOLATOR COSTS IN US $
NET SAVINGS IN US $
NET SAVINGS % OF REINFORCEMENT
10 40980 25 24926 16054 7.75
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
32
% SAVINGS IN REINFORCEMENT FOR BEAMS AND COLUMNS VERSUS DIFFERENT STORIES
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
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.
35
REFERENCES
BANGLADESH NATIONAL BUILDING CODE(19993) HOUSING AND BUILDING RESEARCH INSTITUTE
DEB S.K(2004) “SEISMIC BASE ISOLATION – AN OVERVIEW”
36
THANK YOU
