BRIDGE RESPONSE TO NEAR-FIELD GROUND...

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BRIDGE RESPONSE TO BRIDGE RESPONSE TO NEARNEAR--FIELD GROUND MOTIONSFIELD GROUND MOTIONS

Genda Chen*, Ph.D., P.E., and Genda Chen*, Ph.D., P.E., and MostafaMostafa ElEl--EngebawyEngebawy, Ph.D., Ph.D.*Associate Professor of Civil Engineering*Associate Professor of Civil Engineering

Department of Civil, Architecture and Environmental EngineeringDepartment of Civil, Architecture and Environmental EngineeringUniversity of MissouriUniversity of Missouri--RollaRolla

[email protected]@umr.edu

Geotechnical and Bridge Seismic Design WorkshopGeotechnical and Bridge Seismic Design WorkshopNew Madrid Seismic Zone ExperienceNew Madrid Seismic Zone Experience

October 28October 28--29, 2004 29, 2004

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ParticipantsParticipants

Genda Chen, Ph.D., P.E. (Team Leader)Genda Chen, Ph.D., P.E. (Team Leader)MostafaMostafa ElEl--EngebawyEngebawy, Ph.D., Ph.D.

RonaldoRonaldo Luna, Ph.D., P.E.Luna, Ph.D., P.E.Richard Stephenson, Ph.D., P.E.Richard Stephenson, Ph.D., P.E.

WeiWei ZhengZheng, Ph.D. Graduate Student, Ph.D. Graduate StudentWenxigWenxig Liu, Ph.D. Graduate StudentLiu, Ph.D. Graduate Student

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Outline of PresentationOutline of PresentationObjectivesObjectivesDescription of Bridge SystemsDescription of Bridge SystemsFoundation Model and Bridge ModelFoundation Model and Bridge ModelDynamic Characteristics of Selected BridgesDynamic Characteristics of Selected BridgesDiscussion of ResultsDiscussion of Results

Influence of Rupture DirectivityInfluence of Rupture DirectivityInfluence of Vertical AccelerationInfluence of Vertical AccelerationInfluence of LiquefactionInfluence of LiquefactionComparison with FarComparison with Far--Field Ground MotionsField Ground Motions

Concluding RemarksConcluding RemarksRecommendations for including NearRecommendations for including Near--Field Effects in Field Effects in Highway Bridge DesignHighway Bridge Design

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ObjectivesObjectives

To evaluate the response of a multiTo evaluate the response of a multi--span simply span simply supported bridge (L472) and a multisupported bridge (L472) and a multi--span continuous span continuous bridge (A1466) to nearbridge (A1466) to near--field ground motions from field ground motions from future earthquake scenarios in the NMSZfuture earthquake scenarios in the NMSZTo compare the bridge response subjected to nearTo compare the bridge response subjected to near--field field ground motions simulated using the compositeground motions simulated using the composite--source source model with that of farmodel with that of far--field motions of the pointfield motions of the point--source modelsource modelTo To recommend a simple method for including nearrecommend a simple method for including near--field effects in highway bridge designfield effects in highway bridge design

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Description of L472 BridgeDescription of L472 Bridge

Located on interstate highway I55, Pemiscot CountyLocated on interstate highway I55, Pemiscot CountyMultiMulti--span simply supported (MSSS) bridge span simply supported (MSSS) bridge –– 5 spans5 spansDesigned according to the 1949 AASHO specifications Designed according to the 1949 AASHO specifications without seismic considerationswithout seismic considerations5757oo skewskewLaterallyLaterally--restrained steel plate girders restrained steel plate girders TYPE TYPE ““CC”” fixed and expansion steel bearingsfixed and expansion steel bearingsSupported by deep pile foundationsSupported by deep pile foundations

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Ground surface XZ

X (longitudinal direction)

Y (transverse direction)

12 3

15°

Southwestern segment

Center of span between bents 3–4

O

x'

y'


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Description of A1466 BridgeDescription of A1466 Bridge

Located on interstate highway I55, Pemiscot CountyLocated on interstate highway I55, Pemiscot CountyMultiMulti--span continuous bridge span continuous bridge –– 4 spans4 spansDesigned according to the 1949 AASHO specifications Designed according to the 1949 AASHO specifications without seismic considerationswithout seismic considerations1010oo skewskewLaterallyLaterally--restrained steel plate girders restrained steel plate girders TYPE TYPE ““DD”” fixed and expansion steel bearingsfixed and expansion steel bearingsSupported by deep pile foundationsSupported by deep pile foundations

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Description of A1466 BridgeDescription of A1466 Bridge

Ground surface X

Z

Southwestern segment

X

Y

12° O

x'

y'

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Foundation ModelFoundation Model

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Bridge ModelBridge Model

Initial stiffness of all RC elements to account for Initial stiffness of all RC elements to account for concrete cracking, confinement, reinforcement yielding, concrete cracking, confinement, reinforcement yielding, and expected level of axial forcesand expected level of axial forces

Nonlinear elements to account for:Nonlinear elements to account for:Plastic zones at the top and bottom of columnsPlastic zones at the top and bottom of columnsTYPE TYPE ““CC”” and and ““DD”” expansion bearings expansion bearings PoundingPounding

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Bridge ModelBridge ModelStressStress--Strain RelationsStrain Relations

0

5

10

15

20

25

0.000 0.005 0.010 0.015Compressive strain

Com

p. s

tress

(MPa

) Unconfined concreteConfined concrete

0

100

200

300

400

500

0.00 0.05 0.10 0.15 0.20 0.25Strain

Stre

ss (M

Pa)

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0

100

200

300

400

500

0 0.01 0.02 0.03 0.04 0.05 0.06Curvature (1/m)

Mom

ent (

kN-m

)

0

200

400

600

800

1000

0 0.005 0.01 0.015 0.02Curvature (1/m)

Mom

ent (

kN-m

)

8#7 #[email protected]

0.76m

8#10

0.91m

[email protected]

L472 Bridge ColumnsL472 Bridge Columns A1466 Bridge ColumnsA1466 Bridge Columns

Bridge ModelBridge ModelMomentMoment--Curvature AnalysisCurvature Analysis

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Dynamic Characteristics Dynamic Characteristics L472 Bridge L472 Bridge –– Fundamental mode of vibrationFundamental mode of vibration

TToo = 0.70 sec= 0.70 sec

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Dynamic Characteristics Dynamic Characteristics L472 Bridge L472 Bridge –– Second mode of vibrationSecond mode of vibration


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Dynamic Characteristics Dynamic Characteristics A1466 Bridge A1466 Bridge –– Fundamental mode of vibrationFundamental mode of vibration


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Dynamic Characteristics Dynamic Characteristics A1466 Bridge A1466 Bridge –– Second mode of vibrationSecond mode of vibration


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Discussion of ResultsDiscussion of Results

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Influence of Rupture Directivity (L472)Influence of Rupture Directivity (L472)

36°N

37°N

Latit

ude

Southwestern segment L472 bridge site Epicenter #32

36°N

37°NLa

titud

e Southwestern segment L472 bridge site Epicenter #82

X COS X COS θθ is NAis NA

X COS X COS θθ = 0.45= 0.45

MMW W 7.0 7.0

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-2.0

-1.0

0.0

1.0

2.0

0 20 40 60 80Time (sec)

Vel

ocity

(m/s

ec)

-2.0

-1.0

0.0

1.0

2.0

0 20 40 60 80Time (sec)

Vel

ocity

(m/s

ec)

Sim #82 Sim #82 –– FN rock motion FN rock motion with velocity pulseswith velocity pulses

Sim #32 Sim #32 –– FN rock motionFN rock motionwithout velocity pulseswithout velocity pulses

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-2.0

-1.0

0.0

1.0

2.0

0 20 40 60 80Time (sec)

Vel

ocity

(m/s

ec)

-2.0

-1.0

0.0

1.0

2.0

0 20 40 60 80Time (sec)

Vel

ocity

(m/s

ec)

Sim #82 Sim #82 –– FN ground motion FN ground motion with velocity pulseswith velocity pulses

Sim #32 Sim #32 –– FN ground motionFN ground motionwithout velocity pulseswithout velocity pulses

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Sim #82 Sim #82 –– FN ground motion FN ground motion with displacement pulseswith displacement pulses

Sim #32 Sim #32 –– FN ground motionFN ground motionwithout displacement pulseswithout displacement pulses

-2.0

-1.0

0.0

1.0

2.0

0 20 40 60 80Time (sec)

Dis

plac

emen

t (m

)

-2.0

-1.0

0.0

1.0

2.0

0 20 40 60 80Time (sec)

Dis

plac

emen

t (m

)

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3.23.23.13.1dd2.72.72.52.5cc2.82.82.32.3bb2.32.31.71.7aa

Sim Sim #82#82

Sim Sim #32#32LocationLocation

Bent Bent # 2# 2

Bent Bent # 3# 3

Bent Bent # 1# 1

aa

bbcc

dd

MMW W 7.0 7.0

InIn--planeplanecurvature ductilitycurvature ductility

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Influence of Vertical Acceleration (L472)Influence of Vertical Acceleration (L472)

--897897--16621662dd

--12791279--17411741cc

--796796--16791679bb

--10061006--13861386aa

withoutwithoutVV

withwithVV

LocationLocation

Bent Bent # 2# 2

Bent Bent # 3# 3

Bent Bent # 1# 1

aa

bbcc

dd

MMW W 7.5 7.5

Compressive forceCompressive force

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Influence of Vertical Acceleration (L472)Influence of Vertical Acceleration (L472)

9.49.48.18.1dd

8.18.16.76.7cc

6.56.55.65.6bb

5.35.34.24.2aa

withoutwithoutVV

withwithVV

LocationLocation

Bent Bent # 2# 2

Bent Bent # 3# 3

Bent Bent # 1# 1

aa

bbcc

dd

MMW W 7.5 7.5


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Influence of Liquefaction (A1466)Influence of Liquefaction (A1466)

-30

-25

-20

-15

-10

-5

0

40 60 80 100 120Maximum displacement (cm)

Dep

th fr

om to

p of

em

bank

men

t (m

)

Nonliquefied

Liquefied-30

-25

-20

-15

-10

-5

0

40 60 80 100 120Maximum displacement (cm)

Dep

th fr

om to

p of

em

bank

men

t (m

)

Nonliquefied

Liquefied

Maximum FP displacementsMaximum FP displacements

MMW W 7.0 7.0 –– Sim #12Sim #12

Maximum FN displacementsMaximum FN displacements

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FP at bottom of embankmentFP at bottom of embankment FN at bottom of embankmentFN at bottom of embankment

MMW W 7.0 7.0 –– Sim #12Sim #12

-1.0

-0.5

0.0

0.5

1.0

0 20 40 60 80Time (sec)

Dis

plac

emen

t (m

)

Liquefied Nonliquefied

-1.0

-0.5

0.0

0.5

1.0

0 20 40 60 80Time (sec)

Dis

plac

emen

t (m

)


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FP at top of embankmentFP at top of embankment FN at top of embankmentFN at top of embankment

-1.0

-0.5

0.0

0.5

1.0

0 20 40 60 80Time (sec)

Dis

plac

emen

t (m

)


-1.0

-0.5

0.0

0.5

1.0

0 20 40 60 80Time (sec)

Dis

plac

emen

t (m

)


MMW W 7.0 7.0 –– Sim #12Sim #12

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MMW W 7.0 7.0 –– Sim #12Sim #12

6.36.318.918.9dd

6.46.431.031.0cc

6.16.120.220.2bb

6.36.331.631.6aa

without without LIQLIQ

withwithLIQLIQ

LocationLocation

Bent Bent # 2# 2

Bent Bent # 3# 3Abutment Abutment

# 1# 1

aa

bb

cc

dd


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Comparison with FarComparison with Far--Field MotionsField Motions

Rock motionsRock motions Ground motionsGround motions

0

1

2

3

4

5

0 1 2 3 4 5Period (sec)

Spec

tral a

ccel

erat

ion

(g)

Fault-parallel Fault-normal Point-source

0

1

2

3

4

5

0 1 2 3 4 5Period (sec)

Spec

tral a

ccel

erat

ion

(g)

Fault-parallel Fault-normal Point-source

MMW W 7.5 7.5 –– L472L472

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Motions applied along the Motions applied along the longitudinal axislongitudinal axis of the bridgeof the bridge

MMW W 7.5 7.5 –– L472L472

2.32.36.76.7dd

1.81.85.95.9cc

1.91.95.25.2bb

1.61.64.44.4aa

PointPoint--sourcesource

CompositeComposite--sourcesource

LocationLocation

Bent Bent # 2# 2


# 1# 1

aa

bb

cc

dd


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Motions applied along the Motions applied along the transverse axistransverse axis of the bridgeof the bridge

MMW W 7.5 7.5 –– L472L472

1.31.34.54.5dd

1.11.14.04.0cc

1.11.13.23.2bb

1.01.02.72.7aa

PointPoint--sourcesource

CompositeComposite--sourcesource

LocationLocation

Bent Bent # 2# 2


# 1# 1

aa

bb

cc

dd


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Recommendations for Recommendations for including Nearincluding Near--Field Effects Field Effects in Highway Bridge Designin Highway Bridge Design

Based on AbrahamsonBased on Abrahamson’’s model (2000) and s model (2000) and Somerville et al. (1997) Somerville et al. (1997)

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Directivity modelDirectivity model

STEP ISTEP IScale factor for the average horizontal component AvH Scale factor for the average horizontal component AvH (after Abrahamson, 2000)(after Abrahamson, 2000)

ln[Dir(X, ln[Dir(X, θθ, T)] = C1(T) + 1.88 C2(T) XCos, T)] = C1(T) + 1.88 C2(T) XCosθθ XCosXCosθθ ≤≤ 0.40.4ln[Dir(X, ln[Dir(X, θθ, T)] = C1(T) + 0.75 C2(T) XCos, T)] = C1(T) + 0.75 C2(T) XCosθθ > 0.4> 0.4

STEP IISTEP IIDifference between FN and FP components of motion Difference between FN and FP components of motion (after Somerville et al., 1997) (after Somerville et al., 1997)

ln(FN/AvH) = Cos(2ln(FN/AvH) = Cos(2θθ) [C3(T) + C4(T) ln(r) [C3(T) + C4(T) ln(rruprup+1) + C5(M+1) + C5(MWW--6)] 6)] θθ < 45< 45°°ln(FN/AvH) = 0 ln(FN/AvH) = 0 θθ ≥≥ 4545°°ln(FP/AvH) = ln(FP/AvH) = --ln(FN/AvH) ln(FN/AvH)

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Upper bound of Directivity ConditionsUpper bound of Directivity Conditions

Assuming XCosAssuming XCosθθ=0.40 then =0.40 then θθ=4.4=4.4°° for for L472 bridge (3.7 km from fault)L472 bridge (3.7 km from fault)

L472 site - Mw 7.5

0.0

1.0

2.0

3.0

4.0

0 1 2 3 4 5Period (sec)

Spec

tral A

ccel

erat

ion

(g)

Fault-parallel

FP upper bound

ATC/MCEER

L472 site - Mw 7.5

0.0

1.0

2.0

3.0

4.0

5.0

0 1 2 3 4 5Period (sec)

Spec

tral A

ccel

erat

ion

(g)

Fault-normal

FN upper bound

ATC/MCEER

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Upper bound of Directivity ConditionsUpper bound of Directivity Conditions

Assuming XCosAssuming XCosθθ=0.40 then =0.40 then θθ=12.5=12.5°° for for A1466 bridge (10.9 km from fault)A1466 bridge (10.9 km from fault)

A1466 site - Mw 7.5

0.0

1.0

2.0

3.0

0 1 2 3 4 5Period (sec)

Spec

tral A

ccel

erat

ion

(g)

Fault-parallel

FP upper bound

ATC/MCEER

A1466 site - Mw 7.5

0.0

1.0

2.0

3.0

0 1 2 3 4 5Period (sec)

Spec

tral A

ccel

erat

ion

(g)

Fault-normal

FN upper bound

ATC/MCEER

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Average Directivity ConditionsAverage Directivity Conditions

Assuming the epicenter at the middle of the fault then XCosAssuming the epicenter at the middle of the fault then XCosθθ=0.24 and =0.24 and θθ=19.5=19.5°° for for A1466 bridge (10.9 km from fault)A1466 bridge (10.9 km from fault)

A1466 site - Mw 7.5

0.0

1.0

2.0

3.0

0 1 2 3 4 5Period (sec)

Spec

tral A

ccel

erat

ion

(g)

Fault-parallel

Average directivity

ATC/MCEER

A1466 site - Mw 7.5

0.0

1.0

2.0

3.0

0 1 2 3 4 5Period (sec)

Spec

tral A

ccel

erat

ion

(g)

Fault-normal

Average directivity

ATC/MCEER

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Concluding RemarksConcluding Remarks

The curvature ductility ratio of columns increase significantly The curvature ductility ratio of columns increase significantly with the moment magnitude. Forward rupture directivity and with the moment magnitude. Forward rupture directivity and liquefaction effects are the dominant reasons for the high ratioliquefaction effects are the dominant reasons for the high ratioss

The vertical acceleration increases the compressive forces in thThe vertical acceleration increases the compressive forces in the e columns under the maximum considered earthquake. They are columns under the maximum considered earthquake. They are remarkably reduced with lower moment magnitudesremarkably reduced with lower moment magnitudes

Liquefaction yields large displacements in the faultLiquefaction yields large displacements in the fault--normal normal direction and permanent offset of the soil near the top of the direction and permanent offset of the soil near the top of the embankment that develop extreme large deformations in the embankment that develop extreme large deformations in the plane of the bridge bents leading to large inplane of the bridge bents leading to large in--plane curvature plane curvature ductility ratios of the columnsductility ratios of the columns

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RecommendationsRecommendations

A siteA site--specific rock and ground motion simulations are specific rock and ground motion simulations are recommended for highway bridges within 10 km from active recommended for highway bridges within 10 km from active faults in the NMSZ. The resulting rock motions should include faults in the NMSZ. The resulting rock motions should include forward rupture directivity while fling step is not likely to ocforward rupture directivity while fling step is not likely to occur cur in future earthquake eventsin future earthquake events

For highway bridges located beyond 10 km, a simple For highway bridges located beyond 10 km, a simple methodology is recommended for considering nearmethodology is recommended for considering near--field effects field effects in their design response spectra based on the average directivitin their design response spectra based on the average directivity y conditions at the site and the directivity models of Abrahamson conditions at the site and the directivity models of Abrahamson (2000) and Somerville et al. (1997)(2000) and Somerville et al. (1997)

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