seismic isolation of bridges and mission-critical...

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MULTIDISCIPLINARY CENTER FOR EARTHQUAKE ENGINEERING RESEARCH

Seismic Isolation of Bridges and Mission-Critical Infrastructure

Professor Andrew Whittaker, S.E.Professor Michael Constantinou

Department of Civil, Structural and Environmental EngineeringUniversity at Buffalo

University at Buffalo, State University of New York

Overview of presentation

• Seismic protective systems• Basic principles of operation• Hardware• Codes and guidance • Full-scale testing• Applications

– Bridges– Infrastructure

• Protective systems research at UB

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Seismic protective systems

MetallicFrictionViscoelasticViscous

Hybrid Systems

Seismic Isolation

Passive Damping

Semi-Activeand ActiveDamping

Smart Materials

Elastomeric Lead-rubberSliding (FP)

Variable Stiffnessand Damping

Mass Damper

ER FluidMR FluidSMA


Principles of seismic isolation

3


Seismic isolation hardware


Elastomeric bearings

• Production– Compression mold

Seismic bearings– 1.5 m diameter

– Injection mold• Used for small bearings

• Vulcanization – Pressure – Temperature profile– Effect of variations in

profile

4


Elastomeric bearings

• Low-damping natural rubber– Shear modulus in psi

75 min, 95 ave, 125 max

– Damping in the range of 2% to 6%– Temperature dependence

• High-damping rubber– Shear modulus in psi

55 min, 200 max

– Damping in the range of 7% to 14%– Properties depend on scragging, recovery,

aging, velocity, load-history, axial pressure


High-damping rubber bearings

-12

-8

-4

0

4

8

12

-300 -200 -100 0 100 200 300

Shear strain (%)

Shea

r for

ce (k

ips)

5


Lead-rubber bearings


Lead-rubber bearings

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Friction Pendulum™ bearing



7




Eradiquake™ bearing

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Fluid viscous dampers


Nonlinear VD, ± 175 mm, 1 m/sec, 665 kN

Fluid viscous dampers

-200

-150

-100

-50

0

50

100

150

200

-7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7

Displacement (in)

Forc

e (k

ips)

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• Mandatory for – Bridges (AASHTO)– Buildings (NEHRP)– Nuclear (ASCE-4-98)

• Protocols– Prototype

Travel, braking, thermalSeismic

– ProductionQuality control

• Velocity effects– Static testing– Dynamic testing

Testing of seismic isolators and dampers


Bridge applications

EEL RIVER BRIDGE, CALIFORNIALEAD-RUBBER BEARINGS

KODIAK, ALASKAFP BEARINGS

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Codes and guidance

• 1999 AASHTO Guide Specification for Seismic Isolation Design– Analysis

Linear, nonlinear dynamic– Design– Testing

• 2003 NEHRP Recommended Provisions– Analysis, design, testing

• FHWA/Caltrans Technical Report on service and seismic design of protective hardware– Constantinou, Whittaker, et al.– 2007

• CERF/HITEC reports• Reports, manuals, books


Bridge applications

BENICIA-MARTINEZ BRIDGESAN FRANCISCO BAY AREA

FP BEARINGS

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Infrastructure applications

LNG TANKS, REVITHOUSSA, GREECEFP BEARINGS


Infrastructure applications

LNG TANKS, INCHON, KOREAELASTOMERIC BEARINGS

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Applications: Sakhalin II gas platforms



• Mission-critical application— Protection of USD $10+B

• Application of seismic protective technologies

• Seismic isolation bearings under extreme compressive loading― Gravity: 7,000 tons― DLE: 15,000 tons

• Artic temperatures (-60ºF)• Challenges

― Isolator sizing― Heat flux calculations― Simplified dynamic analysis― Testing

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• Maintain average and edge pressure• Maintain thickness of liner• Scale overlay thickness• Bearing thicknesses to maintain thermodynamic conditions• Testing procedure to simulate temperature rise due to frictional

heating (related to liner wear)

0

100

200

300

400

0 10 20 30 40Time (sec)

Tem

pera

ture

rise

(o C

)

Bidirectional seismic motion with varying axial load

Unidirectional sinusoidal motion, 250 mm amplitude, 0.6 Hz, 7 cycles, 33.6 N/mm2 pressure



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Protective systems research at UB

• Hardware development– Lead-rubber bearings– Double concave FP bearings– XY FP bearings

• Systems development– Bridges– Nuclear structures


11

11

11

22

22

R2

R1

Pivot Point

22

d d

h2

h1

u=u2

u1u2

u=u1+u2=2d

Double concave FP bearing (Fenz)

• Variant on the FP bearing– Two sliding surfaces

• Radii: R1 and R2

• Friction: µ1 and µ2

– Large displacement capacity• Nearly double that of FP

bearing with same plan dimensions

• Analytical formulations• Component testing

– Local behavior• Earthquake simulator testing

– System behavior

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DC-FP bearing component tests

Equal Radii and Equal Friction Specimen

Total Displacement, u (mm)

-125 0 125

Late

ral F

orce

Ver

tical

For

ce

-0.2

0.0

0.2

ExperimentalAnalytical

Top Displacement, u1 (mm)

-125 0 125

Late

ral F

orce

Ver

tical

For

ce

-0.2

0.0

0.2

Bottom Displacement, u2 (mm)

-125 0 125

Late

ral F

orce

Ver

tical

For

ce

-0.2

0.0

0.2

R1+R2-h1-h2=880 mm

R2-h2=442 mm

R1-h1=438 mm

µ1=0.058

µ2=0.057

Unequal Radii and Unequal Friction Specimen

Total Displacement, u (mm)

-125 0 125

Late

ral F

orce

Ver

tical

For

ce

-0.15

0.00

0.15

ExperimentalAnalytical

Top Displacement, u1 (mm)

-125 0 125

Late

ral F

orce

Ver

tical

For

ce

-0.15

0.00

0.15

Bottom Displacement, u2 (mm)

-125 0 125

Late

ral F

orce

Ver

tical

For

ce-0.15

0.00

0.15

R1+R2-h1-h2=1168 mm

R2-h2=442 mm

R1-h1=726 mm

µ1=0.038

µ2=0.021


DC-FP bearing system tests

100% NR Sylmar 90o Longitudinal Excitation

Isolation System Displacement (mm)-125 -100 -75 -50 -25 0 25 50 75 100 125

Tota

l Bas

e S

hear

Tota

l Ver

tical

Loa

d

-0.15

-0.10

-0.05

0.00

0.05

0.10

0.15

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XY-FP bearing (Marin)

• Variant on the FP bearing– Orthotropic bearing

• Radii: R1 and R2

• Friction: µ1 and µ2

– Independent sliding along each rail

– Resistance to tensile axial loads

• Analytical formulations• Component testing

– Local behavior• Earthquake simulator

testing– System behavior


Vertical stiffness of rubber bearings (Warn)

• Influence of lateral displacement on vertical stiffness

• Improved models of elastomeric bearings

• Analytical studies

– Two spring model

• Finite element studies

• Component testing

– Single bearing test machine

• Earthquake simulator testing

– UB NEES facility

P

FH

θs

δv

u

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Vertical stiffness of rubber bearings

0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.250

0.2

0.4

0.6

0.8

1

1.2

u/R

Kv /

(EcA

/Tr )

Two-spring LDR 5, ρ=2.75 MPaLDR 5, ρ=5.2 MPa LDR 5, ρ=9 MPa

u =152 mm



0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.250

0.2

0.4

0.6

0.8

1

1.2

u/R

Kv /

(EcA

/Tr )

Two-spring LDR 5, ρ=2.75 MPaLDR 5, ρ=5.2 MPa LDR 5, ρ=9 MPa

u =152 mm

(Ave. Crit.: 75%)S, Mises

+6.544e+00+3.845e+03+7.684e+03+1.152e+04+1.536e+04+1.920e+04+2.304e+04+2.688e+04+3.072e+04+3.455e+04+3.839e+04+4.223e+04+4.607e+04

Step: Step-1Increment 17: Step Time = 1.000Primary Var: S, MisesDeformed Var: U Deformation Scale Factor: +1.000e+00

Low damping rubber bearingODB: LDRM2N0H100VC05.odb ABAQUS/STANDARD Version 6.5-1 Wed Aug 17 08:13:11 EDT 2005

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2

3

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• Simulator system studies– 2 NEES 6 DOF simulators

• Bridge model– Weight = 90,000 lbs– Span = 35 ft

• Two isolation systems– Lead-rubber– Low-damping rubber

• Earthquake simulation program– Triaxial inputs

• Study influence of vertical stiffness on rocking response

• Provide data to validate new mathematical models– OpenSees, Matlab, 3D-Basis


Heating of lead cores (Kalpakidis)

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Heating of lead cores

• Thermal analysis – Predict change in isolator

mechanical properties • Input energy• Lead core diameter• Bearing geometry

– Heat conduction through• Shim plates• End plates

• Analytical studies– Transient response– Steady state response

• Finite element studies

0

50

100

150

200

250

300

350

400

0 5 10 15 20 25 30r (cm)

Tem

pera

ture

(o C

)


Closing Remarks

• Seismic isolation– Relatively mature technology

Elastomeric and sliding isolators

– ApplicationsBridgesInfrastructure

– Opportunities for improvement in hardware and systems

– On-going research program at UB

seismic isolation of bridges and mission-critical...

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