structural dynamics & vibration control lab., kaist, korea 1 a comparative study on aseismic...
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Structural Dynamics & Vibration Control Lab., KAIST, KoreaStructural Dynamics & Vibration Control Lab., KAIST, Korea 11
A Comparative Study on Aseismic Performances ofBase Isolation Systems for Multi-span Continuous Bridge
Kyu-Sik Park, Graduate Student, KAIST, Korea
Sang-Won Cho, Graduate Student, KAIST, Korea
In-Won Lee, Professor, KAIST, Korea
The 14th KKNN Seminar on Civil EngineeringNovember 5 - 7, 2001, Kyoto, Japan
Structural Dynamics & Vibration Control Lab., KAIST, KoreaStructural Dynamics & Vibration Control Lab., KAIST, Korea 22
CONTENTS
Introduction
Aseismic Base Isolation Systems
Sensitivity Analysis
Conclusions
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A comparative study on aseismic performances of various base isolation systems (BISs) for the critical design parameters has been rarely done.
Most of previous studies are focused on the building structures in spite that BISs are widely used for the bridge structures.
INTRODUCTION
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Objective A comparative study on aseismic performances of BISs
for multi-span continuous bridgefor critical design parameters
To evaluate
aseismic performances of BISssuitable earthquake-resistance design of structures
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M
gx
1x
ASEISMIC BASE ISOLATION SYSTEMS
1. Pure Friction (PF) System
the simplest devicelimits a maximum acceleration transmitted from the
substructuremay have an excessive defection or a residual deformationmay be used economically in the simple or small-
scale structure
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Aseismic Base Isolation Systems
RubberInner steel plate
Outer steel plate
Protective rubber
Flange
gx
1x
M
K
C
2. Rubber Bearing (RB) System
widely studied and used over the world consists of alternating layers of rubber and steel plateparallel action of spring and dashpotmainly shifts natural period of the isolated structure
Structural Dynamics & Vibration Control Lab., KAIST, KoreaStructural Dynamics & Vibration Control Lab., KAIST, Korea 77
3. Lead Rubber Bearing (LRB) System
widely studied and used over the worldadditional energy dissipation by a central lead corebilinear model of characteristic curve is used
RubberInner steel plate
Outer steel plate
Protective rubber
Flange
Central lead coregx
1x
M
Keff
Ceq
Aseismic Base Isolation Systems
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4. Resilient Friction Base Isolation (R-FBI) System
parallel action of resiliency of rubber and friction
of Teflon coated platehas a recovering force by rubber after sliding
gx
1x
M
K
C
Cover plate
Central rubber core
Peripheral rubber core
Rubber cover
Connecting plate
Sliding ring
Aseismic Base Isolation Systems
Structural Dynamics & Vibration Control Lab., KAIST, KoreaStructural Dynamics & Vibration Control Lab., KAIST, Korea 99
5. Electiricite De France (EDF) System
consists of the elastomeric bearing and the friction
plate in series
behaves as a RB unit during a low-intensity earthquakemay have a residual deformation during a high- intensity earthquake
`
gx
2x
M
K
C
1x
Reinforced neoprene pad
Friction plates
Stud anchor
Aseismic Base Isolation Systems
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SENSITIVIY ANALYSIS
1. Ding-Jin Bridge
a continuous bridge with 15 spansconstructed in the western coast expressway in Koreathe span length of bridge: 725 mthe width of the superstructure: 12.15 mthe longitudinal slope: 0.03%Rayleigh damping with structural damping ratio of 2%
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Sensitivity Analysis
Connection elementBIS element
Pier element
1.80.30.5
H2
3.0
2.5
Pier No. 7
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Sensitivity Analysis
2. Input Earthquake Records
El Centro (N00W, 1940) PGA: 0.348 g, PFR: 1~4 Hz
Mexico City (N90W, 1985) PGA: 0.172 g, PFR: 0~1 Hz
San Fernando (S16E, 1971) PGA: 1.170 g, PFR: 1~5 Hz
PGA: Peak Ground Acceleration
PFR: Predominant Frequency Range
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Time(sec)
Acc
eler
atio
n(g
)
Frequency(Hz)
Mag
nit
ud
e
0 1 0 2 0 3 0 4 0-0 .4
-0 .2
0
0 .2
0 .4
E l C en tro
0 2 4 6 8 1 00
4 0
8 0
1 2 0
1 6 0
2 0 0
E l C en tro
0 1 2 3 4 50
0 .5
1
1 .5
2
2 .5
M ex ico C ity
0 1 5 3 0 4 5 6 0 7 5-0 .2
-0 .1
0
0 .1
0 .2
M ex ico C ity
0 2 4 6 8 1 00
1 0 0
2 0 0
3 0 0
4 0 0
S an F e rn an d o
0 1 0 2 0 3 0 4 0-1 .5
-1
-0 .5
0
0 .5
1
S an F e rn an d o
Sensitivity Analysis
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3. Sensitivity Analysis
Numerical simulation variations in natural period of the isolated bridge variations in friction coefficient of the BIS comparative study for different earthquakes with the selected design parameters
Comparisons the peak displacement of deck to check the serviceability the peak bending moment of the lower end of pier to check the design sectional force
Sensitivity Analysis
1(T 1 ~ 6sec)( 0.02 ~ 0.3)
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Variations in natural period of the isolated bridge
Sensitivity Analysis
1 2 3 4 5 6N atu ra l p erio d (s ec)
0
5
1 0
1 5
2 0
Dis
plac
emen
t (cm
)
0
5
1 0
1 5
2 0
Mom
ent 10
6 (Nm
)
E l C en tro
1 2 3 4 5 6N atu ra l p erio d (s ec)
0
1 0
2 0
3 0
4 0
5 0
6 0
7 0
Dis
plac
emen
t (cm
)
0
1 5
3 0
4 5
Mom
ent 10
6 (Nm
)
M ex ic o C ity
R B _ D is .R B _ M o m en tL R B _ D is .L R B _ M o m en t
1 2 3 4 5 6N atu ra l p erio d (s ec)
0
2 0
4 0
6 0
8 0
Dis
plac
emen
t (cm
)
0
2
4
6
Mom
ent 10
7 (Nm
)
S a n F e rn an d o
Structural Dynamics & Vibration Control Lab., KAIST, KoreaStructural Dynamics & Vibration Control Lab., KAIST, Korea 1616
as the natural period increases, the peak displacement increases whereas the peak bending moment decreases.
the peak responses of bridge subjected to Mexico City earthquake are amplified in the natural period of about2 ~ 3 sec.
the peak responses of bridge with LRB system are smaller than those with a RB unit.
Sensitivity Analysis
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Natural Period(sec)
Dis
pla
cem
ent(
cm) M
omen
t X10
7(Nm
)
Natural Period(sec)
Dis
pla
cem
ent(
cm) M
omen
t X10
6(Nm
)R-FBI System EDF System
1 2 3 4 5 60
3
6
9
1 2
0
1
2
3
4
E l C en tro D is .D is .D is .M o m en tM o m en tM o m en t
1 2 3 4 5 60
1 0
2 0
3 0
4 0
5 0
0
1
2
3
4
M ex ico C ity
1 2 3 4 5 60
1 0
2 0
3 0
4 0
5 0
0
2
4
6
8S an F e rn an d o
1 2 3 4 5 60
5
1 0
1 5
2 0
2 5
0
5
1 0
1 5
2 0
2 5
E l C en tro
1 2 3 4 5 60
1 0
2 0
3 0
4 0
5 0
6 0
7 0
0
5
1 0
1 5
2 0
2 5
3 0
M ex ico C ity
1 2 3 4 5 60
2 0
4 0
6 0
8 0
1 0 0
0
1
2
3
4
S an F e rn an d o
0.02
0.14
0.30
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the peak responses of bridge with R-FBI system
- similar to the response spectrum of each earthquake for
small value of friction coefficient
- as friction coefficient increases, the peak responses are not sensitive to variations in the natural period.
the peak responses of bridge with EDF system
- shows a similar trend to those with RB and LRB systems as friction coefficient increases
- if there is no sliding in the friction plates, the responses of bridge are the same as those with a RB unit.
Sensitivity Analysis
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Variations in friction coefficient of the BIS
Sensitivity Analysis
P F _ D is .P F _ M o m en t
0 .0 2 0 .0 6 0 .1 0 0 .1 4 0 .1 8 0 .2 2 0 .2 6 0 .3 0F ric tio n C o effic ien t
0
2
4
6
8
1 0
Dis
plac
emen
t (cm
)
0
1
2
3
4
Mom
ent 10
7 (Nm
)
E l C en tro
0 .0 2 0 .0 6 0 .1 0 0 .1 4 0 .1 8 0 .2 2 0 .2 6 0 .3 0F ric tio n C o effic ien t
0
5
1 0
1 5
2 0
2 5
Dis
plac
emen
t (cm
)
0 .0
0 .5
1 .0
1 .5
2 .0
Mom
ent 10
7 (Nm
)
M ex ico C ity
0 .0 2 0 .0 6 0 .1 0 0 .1 4 0 .1 8 0 .2 2 0 .2 6 0 .3 0F ric tio n C o effic ien t
0
1 5
3 0
4 5
Dis
plac
emen
t (cm
)
0
1
2
3
4
5
Mom
ent 10
7 (Nm
)
S an F e rn an d o
Structural Dynamics & Vibration Control Lab., KAIST, KoreaStructural Dynamics & Vibration Control Lab., KAIST, Korea 2020
as the friction coefficient increases, the peak displacement decreases whereas the peak bending moment increases.
the most portion of the displacement is sliding deformation and the deformation of pier is negligible.
Sensitivity Analysis
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Friction Coefficient
Dis
pla
cem
ent(
cm) M
omen
t X10
7(Nm
)
Friction Coefficient
Dis
pla
cem
ent(
cm) M
omen
t X10
6(Nm
)R-FBI System EDF System
D is .D is .D is .M o m en tM o m en tM o m en t
1
1
1
2sec
4sec
6sec
T
T
T
0 .0 2 0 .0 6 0 .1 0 0 .1 4 0 .1 8 0 .2 2 0 .2 6 0 .3 00
2
4
6
8
1 0
0
1
2
3
E l C en tro
0 .0 2 0 .0 6 0 .1 0 0 .1 4 0 .1 8 0 .2 2 0 .2 6 0 .3 00
1 0
2 0
3 0
4 0
0
1
2
3
4
M ex ico C ity
0 .0 2 0 .0 6 0 .1 0 0 .1 4 0 .1 8 0 .2 2 0 .2 6 0 .3 00
1 0
2 0
3 0
4 0
5 0
0
1
2
3
4
5
S an F ern an d o
0 .0 2 0 .0 6 0 .1 0 0 .1 4 0 .1 8 0 .2 2 0 .2 6 0 .3 00
5
1 0
1 5
2 0
2 5
0
3
6
9
1 2
E l C en tro
0 .0 2 0 .0 6 0 .1 0 0 .1 4 0 .1 8 0 .2 2 0 .2 6 0 .3 00
2 0
4 0
6 0
0
1 0
2 0
3 0
M ex ico C ity
0 .0 2 0 .0 6 0 .1 0 0 .1 4 0 .1 8 0 .2 2 0 .2 6 0 .3 00
2 5
5 0
7 5
1 0 0
0
1
2
3
S an F e rn an d o
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the peak responses of bridge with R-FBI system
- similar to those with a PF unit as friction coefficient increases
- decrease as friction coefficient increases in natural period of 2 sec for Mexico City earthquake
the peak responses of bridge with EDF system
- when there is no sliding in the upper plate, it behaves like RB and LRB systems.
- amplified like those with RB and LRB system for
Mexico City earthquake
Sensitivity Analysis
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Comparative study for different earthquakeswith the selected design parameters
Sensitivity Analysis
the procedure of selecting design parameters
- calculate the ratio of the peak responses to average value according to the natural period and friction coefficient
, ratio ratioaverage average
D MD M
D M
- select the value of alpha which indicates the relative importance of displacement
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Sensitivity Analysis
1 2 1 2for select selectT T
1 2 1 2for select select
1selectT
1 ratioD
1(1 ) ratioM MratioD
rati
o
1select
1 ratioD
1(1 ) ratioM MratioD
rati
o
2select
2 ratioD
2(1 ) ratioM MratioD
rati
o
2selectT
2 ratioD
2(1 ) ratioM MratioD
rati
o
(In our study 0.5)
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Sensitivity Analysis
D isp lacem en tM o m en t
0
5
1 0
1 5
2 0
Dis
plac
emen
t (cm
)
0
5
1 0
1 5
2 0
Mom
ent 10
6 (Nm
)
R B L R B P -F R -F B I E D F
E l C en tro
0
1 0
2 0
3 0
4 0
5 0
6 0
7 0
Dis
plac
emen
t (cm
)
0
5
1 0
1 5
2 0
Mom
ent 10
6 (Nm
)
R B L R B P -F R -F B I E D F
M ex ico C ity
0
1 0
2 0
3 0
4 0
5 0
Dis
plac
emen
t (cm
)
0
1 0
2 0
3 0
Mom
ent 10
6 (Nm
)
R B L R B P -F R -F B I E D F
S an F e rn an d o
PF System
RB System
LRB System
R-FBI System
EDF System
1
1
1
1
: 0.14
: T 3sec
: T 3sec
: T 3sec, 0.14
: T 4sec, 0.10
the selected design parameters
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the peak displacement of bridge with the rubber type bearing is larger than that with the friction type bearing while bending moments is smaller.
the peak responses of bridge with the friction type bearing are less sensitive to substantial variations in the frequency range and intensity of earthquake excitation.
for the selected design parameters
- R-FBI system has the smallest peak deck displacement
- EDF system has the smallest peak bending moment
Sensitivity Analysis
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0 5 1 0 1 5 2 0T im e (sec)
-3
-2
-1
0
1
2
Def
orm
atio
n (c
m) R D = 0 .6 0 cm
P F S y stem (E l C en tro )
0 2 0 4 0 6 0 8 0T im e (sec)
-2 .5
-2 .0
-1 .5
-1 .0
-0 .5
0 .0
0 .5
Def
orm
atio
n (c
m)
R D = -1 .6 3 cm
P F S y stem (M ex ico C ity )
0 5 1 0 1 5 2 0T im e (sec)
-1 0
0
1 0
2 0
3 0
Def
orm
atio
n (c
m)
R D = 1 5 .7 0 cm
P F S y stem (S an F e rn an d o )
0 1 0 2 0 3 0 4 0T im e (sec)
-2 0
0
2 0
4 0
6 0
Def
orm
atio
n (c
m)
S lid in g d e fo rm a tio nT o ta l d e fo rm a tio n
R D = 1 2 .4 3 cm
E D F S y stem (S an F e rn an d o )
residual deformation
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CONCLUSIONS
As natural period of the isolated bridge increases and as friction coefficient of the device decreases
the peak deck displacement increasesthe peak bending moment decreases
It is important that suitable values determined by the sensitivity analysis, be used in the design parameters of the device instead of fixed ones.
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For the selected design parameters
R-FBI system has the smallest peak deck displacement
EDF system has the smallest peak bending moment
Conclusions
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Thank you for your attention.
Structural Dynamics & Vibration Control Lab., KAIST, KoreaStructural Dynamics & Vibration Control Lab., KAIST, Korea 3131
dK
uK
e f fK
m a xx
m a xF
yx
yFdQ
A r e a d i s s i p a t e d e n e r g y
the bilinear model of characteristic curve of LRB system
Appendix
Structural Dynamics & Vibration Control Lab., KAIST, KoreaStructural Dynamics & Vibration Control Lab., KAIST, Korea 3232
1( ) 0x t
1. PF System( )gMx t Mg
1( ) sgn[ ( )] ( )g gMx t Mg x t Mx t
holds as long asStick mode:
Slip mode:
2. RB System
1 1 1( ) ( ) ( ) ( )gMx t Cx t Kx t Mx t
3. LRB System
1 1 1( ) ( ) ( ) ( )eq eff gMx t C x t K x t Mx t
4. R-FBI System
2eq eq effC MK )2/( 2Deffeq DK
1( ) ( )gMx t Kx t Mg 1( ) 0x t holds as long asStick mode:
1 1 1 1( ) ( ) sgn[ ( )] ( ) ( )gMx t Cx t Mg x t Kx t Mx t Slip mode:
5. EDF System2 2 2( ) ( ) ( ) ( )gMx t Cx t Kx t Mx t 1 2 1 2( ) ( ), ( ) ( )x t x t x t x t Stick mode:
2[ ( ) ( )]gM x t x t Mg
1 1 2 1( ) ( ) sgn[ ( ) ( )]Cx t Kx t Mg x t x t
2 2 1( ) sgn[ ( ) ] ( )gMx t Mg x t x Mx t Slip mode:
holds as long as
Appendix