structural dynamics & vibration control lab., kaist, korea 1 a comparative study on aseismic...

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


CONTENTS

Introduction

Aseismic Base Isolation Systems

Sensitivity Analysis

Conclusions


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


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


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



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


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



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



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



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%



Connection elementBIS element

Pier element

1.80.30.5

H2

3.0

2.5

Pier No. 7



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


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



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


1(T 1 ~ 6sec)( 0.02 ~ 0.3)


Variations in natural period of the isolated bridge


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


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


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


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.



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


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.



Variations in friction coefficient of the BIS


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

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

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


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.



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


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



Comparative study for different earthquakeswith the selected design parameters


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



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


rati

o

2select

2 ratioD


rati

o

2selectT

2 ratioD


rati

o

(In our study 0.5)



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

)


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

)


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


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



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


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.


For the selected design parameters

R-FBI system has the smallest peak deck displacement

EDF system has the smallest peak bending moment

Conclusions


Thank you for your attention.


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


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

structural dynamics & vibration control lab., kaist, korea 1 a comparative study on aseismic...

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